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The Predatory Behavior of Two Wasps, Agenoideus Humilis (Pompilidae) and Sceliphron Caementarium (Sphecidae), on the ORB Weaving Spider Araneus Cornutus (Araneidae)

The Predatory Behavior of Two Wasps, Agenoideus Humilis (Pompilidae) and Sceliphron Caementarium... THE PREDATORY BEHAVIOR OF TWO WASPS, HUMILI8 AND AGENOIDEUS (POMPILIDAE) SCELIPHRON CAEMENTARIUM (SPHECIDAE), ON THE ORB WEAVING SPIDER ARANEUS CORNUTUS (ARANEIDAE)I BY WILLIAM EBERHARD Museum of Comparative Zoology, Harvard University The habits of many wasps have been but much nesting studied, of their Many less is known how they locate and capture prey. on wasps in the families Pompilidae and Sphecidae prey orb weaving spiders, and knowledge of their predatory behavior is crucial to an understanding of the biology of orb weavers. This paper describes of two species of Agenoideus humilis the hunting behavior wasp, caementarium (Pompilidae) and the mud dauber Sceliphron (Sphecidae) which were observed preying on the orb weaver raneus cornutus during July and August, I968, and discusses the signifi- for the spiders. cance of their behavior a of A raneus corn,utus on There was dense population the spider the windows and shingled walls of a cottage on Lincoln Pont in the Huyck Rensselaerville, New York. Spiders spun orbs in Preserve, and sat at the hubs during the night, then (except the early evening left the orbs and crouched in retreats for a tew younger individuals) approximately during the day. The retreats were usually tubular, and often had silk just beyond the mouth. Although most silk-lined, of retreats around the cottage were in cracks beneath shingles, the especially plentiful around windows from which the spiders were there a number of retreats at the lights showed at night, and were edges of window panes (there were cm panes/window) 5 3oX 5 and in the corners of window frames. Retreats like these, which Dr. Levi 1This is part of a thesis done under the direction of H. W. and submitted to the Department of Biology of Harvard University, in of requirements for the PhD degree. The work was partial fulfillment held a Summer Fellowship from the E. N. Huyck done in 1968 while thank the directors and staff of the. Preserve for making Preserve, Inc.; in such surroundings. thank it possible for me to do this work pleasant and for the Dr. H. E. Evans for encouragement identifying wasps, and Mary Eberhard, Robert Jeanne, and William. Shear for helpful com- Jane ments on the manuscript. Specimens of the species observed are deposited the Museum of Comparative Zoology, Cambridge, Mass. in Depto. Universidad del Colombia. Present address: Biologia, Valle, Cali, 243 Psyche [June :44 were not hidden from view, were made of silk, often approximately tubular, and usually open at both ends. The dark-colored spiders contrasted with the white woodwork as they rested in these retreats, and were thus easy to locate visually. Spiders field were in the’ usually impossible to .see because their retreats were generally in curled leaves or under flakes of bark. When sufficiently disturbed during the the spiders dropped day, out of their retreats. Sometimes they reached stopped before they the ground, motionless a hung at the end of their trail lines for short then while, climbed back to their retreats; other times they descended to the ground. Although they often began to crawl as soon as they landed on a flat they usually remained motion- surface, less with their legs pulled their bodies landed tight against when they on irregular surfaces such as grass or leaf litter. Predatory behavior of Agenoideus humilis Agenoideus humilis is relatively rare in the northeastern U.S. and (Evans Yoshimoto I96:) but was not hard to find around the cottage on Lincoln and has previously been collected there by Pond, both Kenneth Cooper in and Robert Matthews in (un- I95: I967 published reports to the Trustees of the E. N. Huyck Preserve, Inc.). Evans and Yoshimoto summarize the literature on the biology of this species, noting that it is often found near buildings. It has been recorded preying on orb weavers in the araneid Neoscona, genera A raneus, and but there are no Coneteira, records of its predatory behavior. Females of A. humilis were. observed hunting for spiders on the walls o,f and windows the cottage. Typically, a wasp walked along the surface of the wall until she encountered a crack between two shingles, then walked up the crack and under the overlapping shingle, often staying out of .sight for seconds or more. The wasps did not investigate every crack they encountered, and often passed two or three before walking up one. They usually showed no obvious reaction when they encountered silk in them. Occasionally a wasp bent her abdomen forward beneath her so that the tip was near her head a.s she entered a crack. Four complete wasp-spider encounters were observed. One in- volved a spider resting in a horizontal retreat at the top edge of a window pane. The after wasp, passing within two cm of another spider in a encountered some silk about two cm below the retreat, retreat and climbed directly to it. She touched the side of the 1970] I/I/asps Eberhard :z45 climbed around one curled her abdomen forward retreat, to end, fell under herself, and moved in. Almost immediately the spider backwards out the other descended to the floor (these observa- end, tions were made on a porch), and began to crawl away. The wasp flew out of for about second.s (perhaps disturbed by my sight 3o same presence, see below), then came back (I assume it was the wasp), flew to the spot directly below the retreat where the spider had landed, and ran around quickly in that area. I could not discern any pattern in the .search that the wasp quickly began search- except farther from By the the wasp ing and farther the original area. time had returned, the spider was about away and climbing along o.5m the wall under the edge of the .second row of shingles. The area of the wasp’s hunt quickly expanded to include the wall, and after about seconds she moved .straight toward the which was about m spider She spider her and once away now. grabbed the with legs stung it on the ventral side of its cephalothorax as soon as she. reached it. The spider showed no defense against the wasp’s attack. It stopped moving as soon as it was and the wasp grabbed it near the stung, one her and drawing it up the base of leg with mandibles began wall. W’asps with spiders always moved backwards, dragging the spider behind and several wasps showed strong tendencies to drag them, their spiders upward. This behavior was probably preparation for a One observed with a flight with the spider. wasp was flying spider, must and judging from the angle of its flight as it came to earth, it have climbed at least o m up a tree that was m from the 5-2o site where it landed. Each wasp dragging a spider paused periodically, released her grip on the spider and flew around for a short while, then returned and the spider a short distance dragged the spider onward. When I moved while a wasp was gone on one of these short the wasp excusions, returned to the spot where she had left the spider and ran around (again I could see no pattern) in that area. When she re- quickly the the ventral of its cephalo- encountered spider she stung it on side thorax. This experiment was repeated several times, and even though the wasp encountered the spider from a different direction each time, she always it in the region. The stinging was evidently stung same released the change in the spider’s since wasps did not by position, normally sting spiders which had not been moved. This behavior may her occur when a wasp fails to completely paralyze a spider with first sting. Psyche [June 24.6 Two wasps were observed attacking spiders which had evidently been driven from their retreats and were hanging at the ends of threads. Each wasp flew close to probably the spider, then (and hit) immediately flew to the floor directly beneath ran the .spider and around quickly. In both cases this first encounter caused the spider to descend only part of the way to the and after a short time floor, the wasp flew back up and buzzed the spider again. T’he quickness with which these floor their wasps searched the below ollowing encounters with spiders suggests the wasps in the case reported above may have been disturbed. One wasp’s encounter with an d. cornutus exuvium was also observed. The skin hung near one entrance of an empty retreat, and when she encountered it her into the wasp inserted sting it two or three times. Two spiders escaped after a wasp encountered them. There was a strong (> kmph) wind blowing when one of them let its retreat and hung on a thread as a wasp entered. wasp flew The down to the spider, but as the let spider out more a gust o thread, o( wind blew it arund the corner the house. The wasp did not ollow but landed on the wall. Another spider was at the mouth it, its, of retreat in the crack between two shingles as a wasp aiproached, and dropped out just as the wasp walked crack. The up the wasp walked on for under the overlapping shingle, stayed out of sight about seconds, then walked on. After about a the spider 15 minute, climbed back up its thread to its retreat. In summary, spiders were always attacked while they were on and those not on surfaces a were driven surfaces, (on thread) to them and then attacked. The wasps used their superior speed and an ability to locate the ventral surface of the spider’.s cephalothorax to sting the spiders into paralysis. The wasps probably did not use vision to locate spiders in their but probably did use it to lo- retreats, cate spiders which fallen from had their retreats and perhaps to locate the general area in which to search tor retreats. Tactile or perhaps chemical stimuli from the skin of a spider released stinging behavior. These observations of the predatory behavior of d. humilis differ dramatically from the description of the of d. predatory behavior sericeus Pompilus by Soyer He (--- sericeus) (195o). saw these wasps hunting the orb weavers d raneus diadematus and Zygiella x-notata, but claimed that the wasps, by flying about until they fell into an orb and then sites to which the web threads searching led, used the spider’s The web to find its retreat. observations above 1970] Eberhard-- IJ/asps indicate that A. humilis did not use cues from the orb to locate the spiders. Although these differences may be due to differences in the species, it seems more likely that Soyer misinterpreted some of the behavior he observed. Predatory behavior of caementarium 8celil)hron 8celipkron caementarium is much than larger A. humilis (length about mm vs. about 8 This mm). species has been recorded tubular stocking its mud cells with spiders in the families Araneidae, Thomi.sidae, Oxyopidae, Anyphaenidae, Salticidae, Clubionidae, Mimetidae, and Lycosidae and Theridiidae, (Muma 945). Jeffers In general, they take spiders commonly on plants found (Rau 935, Muma and 945). Jeffers Two individuals of 8. caementarium were observed searching for d. cornutus on and near the windows of the cottage, and 8 wasp- spider enco.unters were seen. 8. caementarium appeared to use dif- ferent signals than those used by A. humilis The to locate spiders. wasps near hovered the windows, alighting occasionally and some- times walking across a pane or two, then flying on. They apparently oriented visually before landing since they almost always lit either small, on dark spots which contrasted with their background (the white trim of the cottage) in of Occa- or corners window panes. they lit sionally on dark objects (usually masses of dead epheme- ropterans) suspended by spider threads. The contrast between a spot and its background appeared to be more important in deter- mining its attractiveness to a wasp than its shape, as the wasps often landed on dark spots bearing little resemblance to a spider crouching in its retreat. These wasps encountered only the spiders which were resting on the white woodwork of the house. There were d. cornutus orbs on and near the and the window.s, wasps sometimes flew into them as they but the were hunted, wasps strong and heavy enough that freed they quickly themselves. Their hunting behavior was never noticeably altered by such an encounter, indicating that they do not use the presence of a.n orb as a cue signal- ling the presence of a spider. Memory of previous a captures probably influenced the choice 6f site for hunting: after depositing a spider in her nest (about m away), one wasp resumed hunting at the same edge of the same window pane where that spider had just been captured. The intensity of hunting activities at a given site also may be influenced by previous experience at that site. Two windows which were examined only Psyche [June or cursorily not at all during intermittent searches for weeks prior were searched very thoroughly on one day when at least three spiders were captured there. About two weeks hunting intensity had later, returned to the level previous to the burst of captures. The wasps may also establish hunting routes. One individual visited a series of four windows in the same order four times, each time after depositing a new spider in her nest. She caught all the spiders on the third and fourth and the to the windows, later visits first two windows were very brief. When a wasp encountered a silken retreat with a spider in it she immediately pulled and tore at the silk in the side of the retreat with her mandibles. After a few by the wasp, the spider tugs usually left the retreat at from the and de- the end farthest wasp scended on a thread. Spiders usually remained inside vertical retreats longer when the wasp was attacking from leaving the. top below, end hesitantly. One spider moved to the bottom of the retreat where a wasp was pulling, moved back to the when the up top end, and, wasp moved to the top along with it, dropped out the bottom. The wasps pursued the spiders as they struggled out of their retreats and as they fell. Several times a wasp captured a spider just it as she flew On as it fell from the retreat and stung away. the attacked three occasions the spider fell to a windowsill and wasp it there. In each case the wasp grasped the spider with her mandibles and front pair of legs and curled her abdomen forward beneath her body and it. On one occasion a wasp stung a spider four stung times, last on side of its cephalothorax. the three times the ventral then landed Several other times a wasp stung a spider as she flew, and stung it at least once more. On two occasions a spider dropped out of its retreat and hung on a line some distance below after it hit the windowsill and (once wasp the. crawled off that). In one of these the captured cases, spider as it hung, and bent her abdomen forward and stung it as she flew away. In the second she landed on the windowsill after case, seizing the spider and bent her abdomen forward and sideways to. sting it. Usually a wasp paused for several seconds after .stinging spider, and on at least four occasions, the wasp’s mouth was pressed against the mouth region of the spider during this pause. On one occasion the spider was rotated so that its mouth region was next to that of The been fluids from their the wasp. wasps may have ingesting victims’ mouths during these pauses. 1970] Eberhard H/asps Twice a wasp captured and then discarded a very small spider. Both spiders, which were less than half the size of the wasp’s head, were captured at the bottoms of their stung in midair, then retreats, dropped as the wasp resumed hunting. There were a number of ,4. individuals of cornutus hunted on the windows where the wasps which were too large (i.e. larger in diameter than the wasp’s mud cell), but no encounters with these individuals were observed. Some- times the wasps appeared to avoid their retreats. Occasionally paused a hunting wasps and flattened themselves on flat, light-colored surface in the sunlight. These pauses probably functioned to elevate the wasp’s body temperature. The predomi- z/. nantly black coloration of 8. caementarium may (and humilis) function to .speed this process, but this is not certain since many wasps which do not obviously need to collect heat are also black. Wasps attempted to sting three different empty spider skins which near hung empty retreats. Thus the stinging behavior of 8. caemen- tarium is probably released by the stimuli of contact with the surface of the spider, just as it in A. h,umilis. would, is This response be highly adaptive for both wasps when they hunt for spiders which are difficult to see after they drop into litter below the retreat and assume cryptic postures. Apparently contact with arthropod cuticle of all kinds will not release once a S. caementarium a stinging; landed on phalangid (daddy-long-legs), but immediately flew on; the phalangid remained motionless. The wasps did not capture all spiders they encountered. Twice a wasp ailed to react when a spider fell from the retreat she was tearing at. Another relatively small spider blown was some distance as it descended on a thread, and the wasp did not follow it. Two other a times, spider did not leave when a wasp pulled at its retreat, and after several the wasp moved on. Both of these retreats tugs, were exceptional. One was under a large mass of dead ephemer- opterans and spider silk and the pulled wasp at this mass rather than the retreat. The wall of the other was unusually strong because it was quite thick and made of thick fibers spun by a relatively large spider. The observations above are not in complete agreement with pub- lished observations of 8. caementarium predatory behavior. The. Peckhams also saw this species = 1905 P:eloaeus caementarium) /lrane.us hunting cornutus ( on the side of a Else’ira strix) house, but recorded that the wasps walked along the wall and into pried nooks and crannies rather than hovering nearby and landing on dark Psyche [June 25o They only followed spots. also recorded that the wasps seldom spiders which fell from their retreats. These differences may be due to differences in cues learned by individual wasps. Discussion T’he hunting behaviors reported above illustrate selective pressures on .4. cornutus and o.ther orb weavers. A spider at the hub of an is safe from by preda- orb in the daylight probably relatively attacks but tors not strong and heavy enough to escape easily from its web, it is very vulnerable to attacks by large, visually orienting, versatile predators such as S. caementarium. On the other many hand, insects fly only the day, and it is certainly advantageous for during the such stabilimenta the spider to use its web during day. Devices as Cyclosa, found in webs of drgioIe, Uloborus, and others (Gertsch which obscure the spider’s outline, a "stopping mesh" next to 949) the orbs of Metepeira, d rgiope, d raneus, and others (Mc- Nelhila. and signal threads to the web from the hiding Cook 889), leading draneus, place of Zygiella, ,Hytiotes, and others (McCook 889) may all function to hinder attacks by relatively large predators while allowing the spider to capture prey caught in the web during the day, spider off its is relatively safe from larger predators because A web safe it .can crawl into places too small for them, and also relatively from smaller substrate-bound predators because it can escape by ialling and hanging on a thread. A spider in a retreat is probably only especially susceptible to wasps which are relatively good fliers, are about its own which hunt by crawling into tight which size, spider’s behavior. spots, and whose behavior can cope with the escape A larger wasp can attack an orb weaver in its retreat only if it can drive or lure the spider from the retreat. The wasp can only "drive the spider from its retreat if it can find it, and if the retreat is not It can probably only lure it with relatively in a sheltered spot. out complicated behavior like that of Belanogaster junceus (?) which hovers next to the hub of the web and taps it with its antennae and perhaps its front legs to lure the spider to the hub (MacNulty ). It is possible predation has been a selective force in- that wasp fluencing web site selection, as the observations above indicate that 8. caementarium might be less likely to encounter well-scattered webs in cool places. cornut;us d raenus appears to have two effective dose range defenses a quick unobserved exit from its and against wasp attacks" retreat, 1970] Eberhard 14asps cryptic coloration and when it lands below. Both of these posture tactics may help explain why some orb weavers .such as Zygiella litterata (Kaston 948) and Singa haemata 93) build (Nielson retreats with two open and why some such as A. cornutus are ends, crytically colored even though they are hidden the normally during day. The ot: S. behavior d. humilis and caementarium indicate that while there may be selective pressure on orb weavers to hide them- selves, there is probably little or no pressure to hide their webs, at least from these species. REFERENCES H. AND C. M. YOSHIMOTO EVANS, E., The and nesting Pompilidae 1962. ecology behavior o] the (Hymen- optera) the northeastern United States. Misc. Publs ent. Soc. of Am. 3: 67-119. GERT$CH, W. J. 1949. American Spiders. D. Van Nostrand Co., New Inc., Princeton, Jersey. 1-285. pp. B. KASTO, J. 1948. Spiders Connecticut. Conn. State geol. and nat. Hist. Survey, of Bull. 70: 9-874. MACNULTY, B. J. 1961. Field observations on some West Hymenoptera. Proc. S. African Lond. ent. nat. Hist. Soe. 1961" 118-133. H. C. McCooI, American Spiders .their I/’ol. and 1889. and Spinningvork. 1. Webs Nests. Published by the author, Philadelphia. MUMA, M. H., AND W. F. JEFFER$ 1945. Studies the spider prey several mud-dauber grasps. Ann. of of ent. Soe. Am. 38: 245-55. E. NtELSOII, The Spider. 1931. Biology Vol. 1. Levin and Munksgaard, Copen- hagen. PECKHAM, G. W., AND E. G. PECKHAM 1905. Wasps Social and Solitary. Houghton, and Boston. Mifflin, Co., P. RArJ, 1935. The spider prey the mud vasp Sceliphron caementarium Hymen. Ent. ,46: (Araneae, SphetTidae). News 267-270. B. SOYER, 1950. Notes sur les SpheTians et les Pompiles. IX. Les Pompiles des vieux tours. Bull mens. Soc. linn. 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The Predatory Behavior of Two Wasps, Agenoideus Humilis (Pompilidae) and Sceliphron Caementarium (Sphecidae), on the ORB Weaving Spider Araneus Cornutus (Araneidae)

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Abstract

THE PREDATORY BEHAVIOR OF TWO WASPS, HUMILI8 AND AGENOIDEUS (POMPILIDAE) SCELIPHRON CAEMENTARIUM (SPHECIDAE), ON THE ORB WEAVING SPIDER ARANEUS CORNUTUS (ARANEIDAE)I BY WILLIAM EBERHARD Museum of Comparative Zoology, Harvard University The habits of many wasps have been but much nesting studied, of their Many less is known how they locate and capture prey. on wasps in the families Pompilidae and Sphecidae prey orb weaving spiders, and knowledge of their predatory behavior is crucial to an understanding of the biology of orb weavers. This paper describes of two species of Agenoideus humilis the hunting behavior wasp, caementarium (Pompilidae) and the mud dauber Sceliphron (Sphecidae) which were observed preying on the orb weaver raneus cornutus during July and August, I968, and discusses the signifi- for the spiders. cance of their behavior a of A raneus corn,utus on There was dense population the spider the windows and shingled walls of a cottage on Lincoln Pont in the Huyck Rensselaerville, New York. Spiders spun orbs in Preserve, and sat at the hubs during the night, then (except the early evening left the orbs and crouched in retreats for a tew younger individuals) approximately during the day. The retreats were usually tubular, and often had silk just beyond the mouth. Although most silk-lined, of retreats around the cottage were in cracks beneath shingles, the especially plentiful around windows from which the spiders were there a number of retreats at the lights showed at night, and were edges of window panes (there were cm panes/window) 5 3oX 5 and in the corners of window frames. Retreats like these, which Dr. Levi 1This is part of a thesis done under the direction of H. W. and submitted to the Department of Biology of Harvard University, in of requirements for the PhD degree. The work was partial fulfillment held a Summer Fellowship from the E. N. Huyck done in 1968 while thank the directors and staff of the. Preserve for making Preserve, Inc.; in such surroundings. thank it possible for me to do this work pleasant and for the Dr. H. E. Evans for encouragement identifying wasps, and Mary Eberhard, Robert Jeanne, and William. Shear for helpful com- Jane ments on the manuscript. Specimens of the species observed are deposited the Museum of Comparative Zoology, Cambridge, Mass. in Depto. Universidad del Colombia. Present address: Biologia, Valle, Cali, 243 Psyche [June :44 were not hidden from view, were made of silk, often approximately tubular, and usually open at both ends. The dark-colored spiders contrasted with the white woodwork as they rested in these retreats, and were thus easy to locate visually. Spiders field were in the’ usually impossible to .see because their retreats were generally in curled leaves or under flakes of bark. When sufficiently disturbed during the the spiders dropped day, out of their retreats. Sometimes they reached stopped before they the ground, motionless a hung at the end of their trail lines for short then while, climbed back to their retreats; other times they descended to the ground. Although they often began to crawl as soon as they landed on a flat they usually remained motion- surface, less with their legs pulled their bodies landed tight against when they on irregular surfaces such as grass or leaf litter. Predatory behavior of Agenoideus humilis Agenoideus humilis is relatively rare in the northeastern U.S. and (Evans Yoshimoto I96:) but was not hard to find around the cottage on Lincoln and has previously been collected there by Pond, both Kenneth Cooper in and Robert Matthews in (un- I95: I967 published reports to the Trustees of the E. N. Huyck Preserve, Inc.). Evans and Yoshimoto summarize the literature on the biology of this species, noting that it is often found near buildings. It has been recorded preying on orb weavers in the araneid Neoscona, genera A raneus, and but there are no Coneteira, records of its predatory behavior. Females of A. humilis were. observed hunting for spiders on the walls o,f and windows the cottage. Typically, a wasp walked along the surface of the wall until she encountered a crack between two shingles, then walked up the crack and under the overlapping shingle, often staying out of .sight for seconds or more. The wasps did not investigate every crack they encountered, and often passed two or three before walking up one. They usually showed no obvious reaction when they encountered silk in them. Occasionally a wasp bent her abdomen forward beneath her so that the tip was near her head a.s she entered a crack. Four complete wasp-spider encounters were observed. One in- volved a spider resting in a horizontal retreat at the top edge of a window pane. The after wasp, passing within two cm of another spider in a encountered some silk about two cm below the retreat, retreat and climbed directly to it. She touched the side of the 1970] I/I/asps Eberhard :z45 climbed around one curled her abdomen forward retreat, to end, fell under herself, and moved in. Almost immediately the spider backwards out the other descended to the floor (these observa- end, tions were made on a porch), and began to crawl away. The wasp flew out of for about second.s (perhaps disturbed by my sight 3o same presence, see below), then came back (I assume it was the wasp), flew to the spot directly below the retreat where the spider had landed, and ran around quickly in that area. I could not discern any pattern in the .search that the wasp quickly began search- except farther from By the the wasp ing and farther the original area. time had returned, the spider was about away and climbing along o.5m the wall under the edge of the .second row of shingles. The area of the wasp’s hunt quickly expanded to include the wall, and after about seconds she moved .straight toward the which was about m spider She spider her and once away now. grabbed the with legs stung it on the ventral side of its cephalothorax as soon as she. reached it. The spider showed no defense against the wasp’s attack. It stopped moving as soon as it was and the wasp grabbed it near the stung, one her and drawing it up the base of leg with mandibles began wall. W’asps with spiders always moved backwards, dragging the spider behind and several wasps showed strong tendencies to drag them, their spiders upward. This behavior was probably preparation for a One observed with a flight with the spider. wasp was flying spider, must and judging from the angle of its flight as it came to earth, it have climbed at least o m up a tree that was m from the 5-2o site where it landed. Each wasp dragging a spider paused periodically, released her grip on the spider and flew around for a short while, then returned and the spider a short distance dragged the spider onward. When I moved while a wasp was gone on one of these short the wasp excusions, returned to the spot where she had left the spider and ran around (again I could see no pattern) in that area. When she re- quickly the the ventral of its cephalo- encountered spider she stung it on side thorax. This experiment was repeated several times, and even though the wasp encountered the spider from a different direction each time, she always it in the region. The stinging was evidently stung same released the change in the spider’s since wasps did not by position, normally sting spiders which had not been moved. This behavior may her occur when a wasp fails to completely paralyze a spider with first sting. Psyche [June 24.6 Two wasps were observed attacking spiders which had evidently been driven from their retreats and were hanging at the ends of threads. Each wasp flew close to probably the spider, then (and hit) immediately flew to the floor directly beneath ran the .spider and around quickly. In both cases this first encounter caused the spider to descend only part of the way to the and after a short time floor, the wasp flew back up and buzzed the spider again. T’he quickness with which these floor their wasps searched the below ollowing encounters with spiders suggests the wasps in the case reported above may have been disturbed. One wasp’s encounter with an d. cornutus exuvium was also observed. The skin hung near one entrance of an empty retreat, and when she encountered it her into the wasp inserted sting it two or three times. Two spiders escaped after a wasp encountered them. There was a strong (> kmph) wind blowing when one of them let its retreat and hung on a thread as a wasp entered. wasp flew The down to the spider, but as the let spider out more a gust o thread, o( wind blew it arund the corner the house. The wasp did not ollow but landed on the wall. Another spider was at the mouth it, its, of retreat in the crack between two shingles as a wasp aiproached, and dropped out just as the wasp walked crack. The up the wasp walked on for under the overlapping shingle, stayed out of sight about seconds, then walked on. After about a the spider 15 minute, climbed back up its thread to its retreat. In summary, spiders were always attacked while they were on and those not on surfaces a were driven surfaces, (on thread) to them and then attacked. The wasps used their superior speed and an ability to locate the ventral surface of the spider’.s cephalothorax to sting the spiders into paralysis. The wasps probably did not use vision to locate spiders in their but probably did use it to lo- retreats, cate spiders which fallen from had their retreats and perhaps to locate the general area in which to search tor retreats. Tactile or perhaps chemical stimuli from the skin of a spider released stinging behavior. These observations of the predatory behavior of d. humilis differ dramatically from the description of the of d. predatory behavior sericeus Pompilus by Soyer He (--- sericeus) (195o). saw these wasps hunting the orb weavers d raneus diadematus and Zygiella x-notata, but claimed that the wasps, by flying about until they fell into an orb and then sites to which the web threads searching led, used the spider’s The web to find its retreat. observations above 1970] Eberhard-- IJ/asps indicate that A. humilis did not use cues from the orb to locate the spiders. Although these differences may be due to differences in the species, it seems more likely that Soyer misinterpreted some of the behavior he observed. Predatory behavior of caementarium 8celil)hron 8celipkron caementarium is much than larger A. humilis (length about mm vs. about 8 This mm). species has been recorded tubular stocking its mud cells with spiders in the families Araneidae, Thomi.sidae, Oxyopidae, Anyphaenidae, Salticidae, Clubionidae, Mimetidae, and Lycosidae and Theridiidae, (Muma 945). Jeffers In general, they take spiders commonly on plants found (Rau 935, Muma and 945). Jeffers Two individuals of 8. caementarium were observed searching for d. cornutus on and near the windows of the cottage, and 8 wasp- spider enco.unters were seen. 8. caementarium appeared to use dif- ferent signals than those used by A. humilis The to locate spiders. wasps near hovered the windows, alighting occasionally and some- times walking across a pane or two, then flying on. They apparently oriented visually before landing since they almost always lit either small, on dark spots which contrasted with their background (the white trim of the cottage) in of Occa- or corners window panes. they lit sionally on dark objects (usually masses of dead epheme- ropterans) suspended by spider threads. The contrast between a spot and its background appeared to be more important in deter- mining its attractiveness to a wasp than its shape, as the wasps often landed on dark spots bearing little resemblance to a spider crouching in its retreat. These wasps encountered only the spiders which were resting on the white woodwork of the house. There were d. cornutus orbs on and near the and the window.s, wasps sometimes flew into them as they but the were hunted, wasps strong and heavy enough that freed they quickly themselves. Their hunting behavior was never noticeably altered by such an encounter, indicating that they do not use the presence of a.n orb as a cue signal- ling the presence of a spider. Memory of previous a captures probably influenced the choice 6f site for hunting: after depositing a spider in her nest (about m away), one wasp resumed hunting at the same edge of the same window pane where that spider had just been captured. The intensity of hunting activities at a given site also may be influenced by previous experience at that site. Two windows which were examined only Psyche [June or cursorily not at all during intermittent searches for weeks prior were searched very thoroughly on one day when at least three spiders were captured there. About two weeks hunting intensity had later, returned to the level previous to the burst of captures. The wasps may also establish hunting routes. One individual visited a series of four windows in the same order four times, each time after depositing a new spider in her nest. She caught all the spiders on the third and fourth and the to the windows, later visits first two windows were very brief. When a wasp encountered a silken retreat with a spider in it she immediately pulled and tore at the silk in the side of the retreat with her mandibles. After a few by the wasp, the spider tugs usually left the retreat at from the and de- the end farthest wasp scended on a thread. Spiders usually remained inside vertical retreats longer when the wasp was attacking from leaving the. top below, end hesitantly. One spider moved to the bottom of the retreat where a wasp was pulling, moved back to the when the up top end, and, wasp moved to the top along with it, dropped out the bottom. The wasps pursued the spiders as they struggled out of their retreats and as they fell. Several times a wasp captured a spider just it as she flew On as it fell from the retreat and stung away. the attacked three occasions the spider fell to a windowsill and wasp it there. In each case the wasp grasped the spider with her mandibles and front pair of legs and curled her abdomen forward beneath her body and it. On one occasion a wasp stung a spider four stung times, last on side of its cephalothorax. the three times the ventral then landed Several other times a wasp stung a spider as she flew, and stung it at least once more. On two occasions a spider dropped out of its retreat and hung on a line some distance below after it hit the windowsill and (once wasp the. crawled off that). In one of these the captured cases, spider as it hung, and bent her abdomen forward and stung it as she flew away. In the second she landed on the windowsill after case, seizing the spider and bent her abdomen forward and sideways to. sting it. Usually a wasp paused for several seconds after .stinging spider, and on at least four occasions, the wasp’s mouth was pressed against the mouth region of the spider during this pause. On one occasion the spider was rotated so that its mouth region was next to that of The been fluids from their the wasp. wasps may have ingesting victims’ mouths during these pauses. 1970] Eberhard H/asps Twice a wasp captured and then discarded a very small spider. Both spiders, which were less than half the size of the wasp’s head, were captured at the bottoms of their stung in midair, then retreats, dropped as the wasp resumed hunting. There were a number of ,4. individuals of cornutus hunted on the windows where the wasps which were too large (i.e. larger in diameter than the wasp’s mud cell), but no encounters with these individuals were observed. Some- times the wasps appeared to avoid their retreats. Occasionally paused a hunting wasps and flattened themselves on flat, light-colored surface in the sunlight. These pauses probably functioned to elevate the wasp’s body temperature. The predomi- z/. nantly black coloration of 8. caementarium may (and humilis) function to .speed this process, but this is not certain since many wasps which do not obviously need to collect heat are also black. Wasps attempted to sting three different empty spider skins which near hung empty retreats. Thus the stinging behavior of 8. caemen- tarium is probably released by the stimuli of contact with the surface of the spider, just as it in A. h,umilis. would, is This response be highly adaptive for both wasps when they hunt for spiders which are difficult to see after they drop into litter below the retreat and assume cryptic postures. Apparently contact with arthropod cuticle of all kinds will not release once a S. caementarium a stinging; landed on phalangid (daddy-long-legs), but immediately flew on; the phalangid remained motionless. The wasps did not capture all spiders they encountered. Twice a wasp ailed to react when a spider fell from the retreat she was tearing at. Another relatively small spider blown was some distance as it descended on a thread, and the wasp did not follow it. Two other a times, spider did not leave when a wasp pulled at its retreat, and after several the wasp moved on. Both of these retreats tugs, were exceptional. One was under a large mass of dead ephemer- opterans and spider silk and the pulled wasp at this mass rather than the retreat. The wall of the other was unusually strong because it was quite thick and made of thick fibers spun by a relatively large spider. The observations above are not in complete agreement with pub- lished observations of 8. caementarium predatory behavior. The. Peckhams also saw this species = 1905 P:eloaeus caementarium) /lrane.us hunting cornutus ( on the side of a Else’ira strix) house, but recorded that the wasps walked along the wall and into pried nooks and crannies rather than hovering nearby and landing on dark Psyche [June 25o They only followed spots. also recorded that the wasps seldom spiders which fell from their retreats. These differences may be due to differences in cues learned by individual wasps. Discussion T’he hunting behaviors reported above illustrate selective pressures on .4. cornutus and o.ther orb weavers. A spider at the hub of an is safe from by preda- orb in the daylight probably relatively attacks but tors not strong and heavy enough to escape easily from its web, it is very vulnerable to attacks by large, visually orienting, versatile predators such as S. caementarium. On the other many hand, insects fly only the day, and it is certainly advantageous for during the such stabilimenta the spider to use its web during day. Devices as Cyclosa, found in webs of drgioIe, Uloborus, and others (Gertsch which obscure the spider’s outline, a "stopping mesh" next to 949) the orbs of Metepeira, d rgiope, d raneus, and others (Mc- Nelhila. and signal threads to the web from the hiding Cook 889), leading draneus, place of Zygiella, ,Hytiotes, and others (McCook 889) may all function to hinder attacks by relatively large predators while allowing the spider to capture prey caught in the web during the day, spider off its is relatively safe from larger predators because A web safe it .can crawl into places too small for them, and also relatively from smaller substrate-bound predators because it can escape by ialling and hanging on a thread. A spider in a retreat is probably only especially susceptible to wasps which are relatively good fliers, are about its own which hunt by crawling into tight which size, spider’s behavior. spots, and whose behavior can cope with the escape A larger wasp can attack an orb weaver in its retreat only if it can drive or lure the spider from the retreat. The wasp can only "drive the spider from its retreat if it can find it, and if the retreat is not It can probably only lure it with relatively in a sheltered spot. out complicated behavior like that of Belanogaster junceus (?) which hovers next to the hub of the web and taps it with its antennae and perhaps its front legs to lure the spider to the hub (MacNulty ). It is possible predation has been a selective force in- that wasp fluencing web site selection, as the observations above indicate that 8. caementarium might be less likely to encounter well-scattered webs in cool places. cornut;us d raenus appears to have two effective dose range defenses a quick unobserved exit from its and against wasp attacks" retreat, 1970] Eberhard 14asps cryptic coloration and when it lands below. Both of these posture tactics may help explain why some orb weavers .such as Zygiella litterata (Kaston 948) and Singa haemata 93) build (Nielson retreats with two open and why some such as A. cornutus are ends, crytically colored even though they are hidden the normally during day. The ot: S. behavior d. humilis and caementarium indicate that while there may be selective pressure on orb weavers to hide them- selves, there is probably little or no pressure to hide their webs, at least from these species. REFERENCES H. AND C. M. YOSHIMOTO EVANS, E., The and nesting Pompilidae 1962. ecology behavior o] the (Hymen- optera) the northeastern United States. Misc. Publs ent. Soc. of Am. 3: 67-119. GERT$CH, W. J. 1949. American Spiders. D. Van Nostrand Co., New Inc., Princeton, Jersey. 1-285. pp. B. KASTO, J. 1948. Spiders Connecticut. Conn. State geol. and nat. Hist. Survey, of Bull. 70: 9-874. MACNULTY, B. J. 1961. Field observations on some West Hymenoptera. Proc. S. African Lond. ent. nat. Hist. Soe. 1961" 118-133. H. C. McCooI, American Spiders .their I/’ol. and 1889. and Spinningvork. 1. Webs Nests. Published by the author, Philadelphia. MUMA, M. H., AND W. F. JEFFER$ 1945. Studies the spider prey several mud-dauber grasps. Ann. of of ent. Soe. Am. 38: 245-55. E. NtELSOII, The Spider. 1931. Biology Vol. 1. Levin and Munksgaard, Copen- hagen. PECKHAM, G. W., AND E. G. PECKHAM 1905. Wasps Social and Solitary. Houghton, and Boston. Mifflin, Co., P. RArJ, 1935. The spider prey the mud vasp Sceliphron caementarium Hymen. Ent. ,46: (Araneae, SphetTidae). News 267-270. B. SOYER, 1950. Notes sur les SpheTians et les Pompiles. IX. Les Pompiles des vieux tours. Bull mens. Soc. linn. 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Journal

Psyche A Journal of Entomology – Wiley

Published: Jan 1, 1970

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