Thieves and freeloaders: Argyrodine kleptoparasites invading cobwebs (Theridiidae) in the arid south-western USA

Biodiversity Data Journal 13: e172851 doi: 10.3897/BDJ.13.e172851 Research Article Thieves and freeloaders: Argyrodine kleptoparasites invading cobwebs (Theridiidae) in the arid south-western USA Jillian Cowles , Ingi Agnarsson ‡ private, Vail, United States of America § Faculty of Life and Environmental Sciences, School of Engineering and Natural Sciences, University of Iceland, Reykjavik, Iceland Corresponding author: Ingi Agnarsson ([email protected]) Academic editor: Jeremy Miller Received: 22 Sep 2025 | Accepted: 03 Nov 2025 | Published: 17 Nov 2025 Citation: Cowles J, Agnarsson I (2025) Thieves and freeloaders: Argyrodine kleptoparasites invading cobwebs (Theridiidae) in the arid south-western USA. Biodiversity Data Journal 13: e172851. https://doi.org/10.3897/BDJ.13.e172851 Abstract Obligate argyrodine kleptoparasites (Theridiidae, Araneae) exploit heterospecific spider webs for food and shelter. Argyrodine spiders are a model lineage for the study of kleptoparasitism and related strategies, yet data on the behaviour of the majority of the over 250 argyrodine species is lacking. Here, we help fill that knowledge gap by documenting the natural history of two poorly-known species. We studied Argyrodes pluto and Neospintharus baboquivari in the webs of two other cobweb spiders, the western black widow (Latrodectus hesperus) and Tidarren sisyphoides, across four sites in southern Arizona. Argyrodes pluto completes its life cycle in L. hesperus webs and specialises on host egg sacs, displacing them to the periphery and feeding on eggs and juveniles; this behaviour appears essential for its reproduction. Neospintharus baboquivari occurs gregariously in both host webs, gleaning small prey. In contrast, N. baboquivari is reportedly a solitary araneophage in the colonial orb webs of Philoponella oweni. We quantified egg sac displacement and describe foraging, mating, egg sac construction and interactions with parasitoids and predators. These findings reveal novel natural history information and expand our understanding of argyrodine behavioural plasticity ‡ § © Cowles J, Agnarsson I. This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Keywords kleptoparasitism, Argyrodinae, Araneophagy, host choice Introduction The Argyrodinae Simon, 1894 comprises > 250 species exploiting webs of other spiders for resources (Vollrath 1987Larcher and Wise 1985, Whitehouse 1986, Cangialosi 1990, Elgar 1993, Guarisco 1999, Pasquet et al. 1997, Agnarsson 2004, Tso and Severinghaus 2000, Vollrath 1979a, Whitehouse 2011, Su and Smith 2014). Strategies range from gleaning prey and sharing prey with the host, to feeding on eggs and spiderlings and even predation on hosts themselves (Vollrath 1979a,Vollrath 1979b, Vollrath 1979a, Smith-Trail 1980, Tanaka 1984, Whitehouse 1986, Cangialosi 1990, Sierwald and Fenzl 1999, Silveira and Japyassú 2012, Agnarsson 2002, Guarisco and Cutler 2018). Some argyrodines also eat silk (Miyashita et al. 2004, Tso and Severinghaus 1998) and araneophages may usurp the host web after killing the host (Gray and Anderson 1989, Larcher and Wise 1985, Pasquet et al. 1997, Cangialosi 1997, Agnarsson 2025a). Host webs are also infiltrated by other invertebrates including kleptoparasitic flies, ectoand endo-parasitic flies and wasps and various others that may compete with the spider kleptoparsites for resources (Miyashita 2001, Agnarsson 2025a). Parasitic arthropods may feed on the host spiders or the host’s or even kleptoparsite eggs (Pierce 1942, Hall 1937, Austin 1985, Kaston 1970, Cushing 1989, Fincke et al. 1990, Guarisco 1999, Barrantes and Weng 2007, Weng and Barrantes 2007, Bibbs and Buss 2012, Triana et al. 2012, Vetter et al. 2012, Gillung and Borkent 2017). While Argyrodinae spiders are a model lineage for the study of kleptoparasitism, data on the behaviour of the majority of the species is lacking or fragmentary. Here we help fill that knowledge gap, using opportunistic observations to document aspects of the natural history of two argyrodine species. While most argyrodines target nephilid and araneid hosts, fewer than 10% inhabit theridiid webs (Whitehouse 2011, Agnarsson 2025a). Amongst these, Argyrodes pluto Banks, 1906 and Neospintharus baboquivari (Exline & Levi, 1962) remain poorly studied (Gertsch 1949, Exline and Levi 1962, Guarisco 1999, Guarisco and Cutler 2018). We examine the natural history and behavioural ecology of A. pluto in L. hesperus webs and N. baboquivari in T. sisyphoides webs. We test whether the presence of A. pluto alters L. hesperus egg sac placement and document kleptoparasite foraging, mating and reproductive behaviour along with interactions with parasitoids and predators. We then compare our findings with the limited prior studies on these species. 2Cowles J, Agnarsson I Material and methods Study sites and surveying Fieldwork occurred July–early December 2018 at four locations in southern Arizona, USA, using direct observation and sweeping. At two sites, kleptoparsites were present:- Vail (32.037180, -110.665145, 1023 m) — front porch and greenhouse in Sonoran Desert thornscrub; A. pluto observed in L. hesperus webs in multiple years prior - Mt Lemmon (32.336187, -110.719474, 1481 m) — grassy meadow and rock structures. At the remaining sites the host L. hesperus was present, but kleptoparasites were absent: Santa Rita Experimental Range (31.761010, -110.845214, 1341 m) — metal building in a wooded riparian grassland - Tucson backyard (32.246029, -110.943065, 744 m) — residential wall and vegetation. Observations and documentation Nocturnal behaviour was recorded under red LED light and photographed (Canon 6D, macro lenses). As the kleptoparasites spend most of their time motionless, observations were made opportunistically during bursts of activity. Wasp parasitoids and egg predators were documented as they entered webs or approached egg sacs. Abandoned L. hesperus egg sacs were collected and examined for parasitoids and ichneumonid cocoons were collected from the web. GPS coordinates via Google Earth Pro; temperature data from AcuRite sensor and Weather Underground. Specimens were identified by Dr. Darrell Ubick (California Academy of Sciences); parasitoid wasps by Drs. James Pitts & David Wahl. In most L. hesperus, webs the female was alone in the web or with one to three adults of A. pluto. Juvenile L. hesperus rapidly emigrated from the web upon exiting the egg sac and were not counted. In some cases as A. pluto spiderlings were emerging from egg sacs, the total number of individuals could exceed 100, but only briefly before these also emigrated. Egg sac displacement assay Egg sacs in five L. hesperus webs without A. pluto (n = 11 sacs) and four webs with A. pluto (n = 13 sacs) were categorised by location: “refuge-entrance” vs. “periphery”. L. hesperus incubates her egg sacs within her refuge and discards empty egg sacs immediately outside the entrance of her refuge after the emergence of the young. Any host egg sacs located away from the refuge-entrance were scored as located in the periphery. Since A. pluto always transported stolen egg sacs tens of centimetres away from the host refuge, scoring egg sac location as refuge-entrance vs. periphery was never ambiguous. Each egg sac was scored only once. If an egg sac was transported even once away from the host refuge, it was scored as being in the periphery. Difference in location was tested using Fisher’s Exact Test (SISA online). Thieves and freeloaders: Argyrodine kleptoparasites invading cobwebs (Theridiidae) ... 3 Behavioral notes Argyrodinine feeding events on prey vs. egg sacs were recorded and, during mating, pedipalp insertion, plug deposition and mating duration were noted. A. pluto egg sac construction was timed and clutch sizes estimated by counting tiny spiderlings hanging in the web near the A. pluto egg sacs. Interactions with predators/parasitoids were documented. Data resources All data are observational and summarised herein. Results Kleptoparasitism and predation Latrodectus hesperus transported captured prey to her retreat, only leaving prey in the web when capturing and wrapping a second prey when already feeding. Argyrodes pluto did not steal prey from the retreat or feed along with the host. In the web, two adult females shared a scarabeid beetle, A. pluto (6 females, a male and a juvenile) fed on the contents of egg sacs on 21 occasions between 9 July and 1 October (Fig. 1Table 1). Feeding entailed chewing holes, secreting a fluid and extracting spiderlings individually with the chelicerae. Argyrodes pluto chased away others, while actively feeding on the contents of the egg sac. However, on one occasion, three adult Argyrodes (two females and one male) took turns to feed on a single stolen egg sac. Latrodectus spiderlings were often seen exiting the holes and escaping predation (Fig. 1). In one instance ~ 70 spiderlings emerged and escaped from an egg sac which A. pluto had predated on for several days. Female# Feeding on L. hesperus egg sac # days feeding Date of A. pluto egg sac # days feeding to egg sac making Date of A. pluto stealing L. hesperus egg sac Comments 1 9-11/07 3 16/07 8 Latrodectus egg sacs 1,2 2 20/07 1 26/07 7 Latrodectus egg sac 3 1 ? ? 22/07 ? Table 1. Timing of Argyrodes pluto association with L. hesperus egg sacs and production of A. pluto egg sacs. 4Cowles J, Agnarsson I Female# Feeding on L. hesperus egg sac # days feeding Date of A. pluto egg sac # days feeding to egg sac making Date of A. pluto stealing L. hesperus egg sac Comments 2 28-29/07 2 1/08 5 Latrodectus egg sac 3, rain 31/07 1 30-31/07 2 8/08 10 Latrodectus egg sac 4 1Latrodectus recovers stolen egg sac 4 (31/07) 1 1/08 attempted 2 2/08 attempted 2 3-6/08 4 3/08 succeeded Latrodectus egg sac 4 2 7/08 Female 2 dead 1 10/08 1 (chews hole in egg sac but does not feed) 10/08 succeeded Stolen egg sac 5 discarded 12/08; wasp larvae 3 18/08 1? 19/08 ? Greenhouse to porch 4 22/08attempted 4 4/09 1? 7/09 4 Greenhouse 3 09/09, 12-13/09 3 19/09 11 Latrodectus egg sac 7, rain 19/09 5 14-16/09, 19/09 3 19/09 6 Latrodectus egg sac 7 6 19/09 1 Latrodectus egg sac 7 5 28/09 succeeded 5 29/09, 1/10 2 11/10 13 Latrodectus egg sac 8 Neospintharus baboquivari was observed only twice feeding in L. hesperus webs, in both cases, juveniles feeding on small prey (Fig. 2). They may have captured these prey on their own as a N. baboquivari juvenile was observed capturing and feeding on a fruitfly in a vial. Thieves and freeloaders: Argyrodine kleptoparasites invading cobwebs (Theridiidae) ... 5 Egg sac stealing and displacement Initiation of egg sac stealing was observed three times. When a host female Latrodectus hesperus began wrapping prey at least 20 cm away from her retreat, Argyrodes pluto immediately abandoned its typically slow gait and dashed straight into the host’s silk retreat (Table 1). The kleptoparasite swiftly cut a host egg sac from the retreat and dragged it to the tunnel entrance (Fig. 1). Host females frequently interrupted preywrapping and rushed back to the retreat upon sensing the intrusion, causing A. pluto to drop to the retreat floor or slip out and remain motionless. If the returning host retrieved and secured the dislodged egg sac, she resumed prey-wrapping after a few minutes, at which point A. pluto renewed its theft attempt; in one instance, requiring three consecutive nights before the theft succeeded. Once a sac was successfully removed, A. pluto rapidly (1-3 minutes) transported it away from the host retreat via silk lines, on one occasion to its own habitual resting area within the host web or by pushing it out of the web. Argyrodes pluto fed on the spiderlings over the next days, sometimes joined by a juvenile and the thief’s abdomen visibly swelled after one to two days of feeding. One stolen egg sac contained wasp larvae that were not eaten. Observed egg sac thefts occurred by A. pluto females prior to, or a few days after, own egg laying; in each case, the nourishment gained enabled the female to produce a subsequent egg sac within 1–2 weeks. On two occasions, a subadult L. hesperus in a nearby web was seen entering the web of its conspecific to feed on the abandoned prey. As the web owner returned, it Figure 1. Argyrodes pluto: A Adult female stealing L. hesperus egg sac, at entrance of silk tunnel refuge; B Adult female transporting a stolen egg sac by attaching silk lines and swinging it away in increments; C Female A. pluto transporting stolen egg sac. The resident L. hesperus had returned to her silk tunnel just after the female A. pluto had the egg sac clear of the tunnel; D Adult male feeding from L. hesperus egg sac, two adult females sharing web. All three fed from the egg sac; E Gravid female feeding on juvenile L. hesperus extracted from egg sac, while other juveniles escape.  6Cowles J, Agnarsson I would strike the web and shake it with her front legs, chasing away the intruding subadult. All 11 egg sacs in kleptoparasite-free webs (n = 5) were located at the refuge, whereas 12 of 13 sacs in occupied webs (n = 4) were placed in the web’s periphery (Table 2, Fisher’s Exact Test, p < 0.001). One that turned out to contain parasitic flies was left by the female L. hesperus at the refuge entrance. Mating and reproduction On 13 July, an Argyrodes pluto couple were found mating in a L. hesperus web and observed for 32 minutes. The female hung ventral‑side up at a slight head‑high incline (Fig. 3), while the male suspended head‑down by leg pairs III–IV, pressing his modified cephalothorax (and clypeal glands) against her chelicerae (Whitehouse 2011). He alternated rapid pedipalp cycles — extension, haematodochal inflation, brief epigynal contact, deflation and withdrawal — each lasting ~ 1–5 s. After several minutes of cycles and brief separations, the male began depositing a semi‑translucent secretion into the female’s genital opening; by the end of mating, this formed a short cylindrical mass above her epigynum (Fig. 3). Within a week, the male vacated the web. Figure 2. Neospintharus baboquivari and its community: A Female N. baboquivari at rest near her egg sac in Tidarren sisyphoides web; B Female N. baboquivari guarding her egg sac. Note remains of small gnat in web; C Argyrodes pluto guarding her egg sac in L. hesperus web. Several N. baboquivari were also present in this web. This female was missing both her front legs; D Male N. baboquivari, missing leg one and two on his right side; E Juvenile N. baboquivari gleaning ant; F Zatypota alborhombarta female from T. sisyphoides web; G Tidarren sisyphoides guarding egg sac in leaf shelter. A pupal cocoon of Zatypota is in the web a few millimetres to the left of the leaf shelter.  Thieves and freeloaders: Argyrodine kleptoparasites invading cobwebs (Theridiidae) ... 7 L. hesperus web, year Location A. pluto present # peripheral egg sacs # egg sacs at refuge Comments 2018 (n = 1) Vail, porch yes 7 1 Flies emerged 2018 (n = 1) Vail, greenhouse yes 2 0 2018 (n = 1) Santa Rita no 0 1 2018 (n = 4) Tucson, city no 0 10 2008 (n = 1) Vail, greenhouse yes 2 0 2015 (n = 1) Vail, porch yes 1 Not known -------------------------------------------------------------------------------------------------------------------------------------------------------------------- A. pluto present 12 1 A. pluto absent 0 11 Fisher's Exact Test p = 0.0000048 Table 2. Location of Latrodectus hesperus egg sacs when A. pluto is present or absent. Below the line a simple contingency table comparing location of egg sacs in the presence or absence of A. pluto. Figure 3. Argyrodes pluto mating: A Haematodocha is inflated and the top of the male's head is placed against the female's chelicerae. No plug at the epigynum is visible yet; B Starting to deposit the plug; C Depositing clear, colourless mating plug. The male continues to hold his head against the female's chelicerae during the deposition of the mating plug; D Plug is complete, visible as a white cylinder extending above the female's epigynum.  8Cowles J, Agnarsson I Both Argyrodes pluto and Neospintharus baboquivari construct and suspend egg sacs within the host web. Argyrodes pluto places successive sacs within a few centimetres of one another and guards each by positioning its body just below the sac neck, front legs extended upwards to deter disturbance. Egg‑sac production by A. pluto consistently follows predation on a Latrodectus hesperus sac (Table 1). Construction begins with a flocculent‐silk tuft on a slender stem, which expands into a goblet shape; eggs and accompanying fluid are then released into the cup, wrapped continuously and the stem, neck and exterior reinforced, a process completed in ~ 4 h (Fig. 4; Suppl. material 1). Finished sacs are urn‑shaped, golden‑tan and darken to brown with humidity. Two female A. pluto produced five egg sacs in the L. hesperus web, one being observed spinning an egg sac three days after mating. About 40 spiderlings emerged a month later, most dying or emigrating within the first week. The first juveniles matured 27 days post‑emergence, a 59 day egg‑to‑maturity interval. We did not observe spiderlings immigrating to the porch web. Juveniles continued to emerge into autumn and a second‑generation female produced an egg sac in mid‑October. By early December, all A. pluto had vanished and the host female was found deceased, clutching her ninth sac. By contrast, N. baboquivari egg sacs, juveniles and adults appear in Tidarren sisyphoides webs in early September, well before any Tidarren host sacs. Its sacs are slimmer than A. pluto´s, bear adhered debris and hang from a straight, rod‑shaped stem Figure 4. Argyrodes pluto egg sac construction: A Cup is built with flocculent silk; B Releasing the eggs and fluid takes only about a minute through the expanded opening of the oviduct. The cup is tipped to receive the eggs. The end of the abdomen develops a dimple or a cleft during egg release; C. Wrapping the eggs in flocculent silk; DBuilding the flat bottom; EBuilding the neck. At this point, the fluid is no longer visible; F Adding fine silk to exterior of sac and to the Y support.  Thieves and freeloaders: Argyrodine kleptoparasites invading cobwebs (Theridiidae) ... 9 • Bibbs C, Buss L (2012) Widow Spider Parasitoids Philolema latrodecti (Fullaway) (Insecta: Hymenoptera: Eurytomidae) and Baeus latrodecti Dozier (Insecta: Hymenoptera: Platygastridae). EDIS 2012 (2). https://doi.org/10.32473/edis-in919-2012 • Cangialosi KR (1990) Life cycle and behavior of the kleptoparasitic spider, Argyrodes ululans (Araneae, Theridiidae. Journal of Arachnology 18: 347‑358. • Cangialosi KR (1997) Foraging versatility and the influence of host availability in Argyrodes trigonum (Araneae, Theridiidae. Journal of Arachnology 25: 182‑193. • Cushing PE (1989) Possible egg-sac defense behaviors in the spider Uloborus glomosus (Araneae: Uloboridae). Psyche 96: 269‑277. https://doi.org/10.1155/1989/97941 • Elgar MA (1993) Inter-specific associations involving spiders: kleptoparasitism, mimicry and mutualism. Memoirs of the Queensland Museum 33 (2): 411‑430. • Elias NU, Wu CY, Su YC (2025) Crack the ‘Blackbox’: A Response to “The Dangers of Data Blackboxing: A Comment on Elias et al., Journal of Biogeography (2024)”. Journal of Biogeography x: e70029. https://doi.org/10.1111/jbi.70029 • Exline H, Levi HW (1962) American spiders of the genus Argyrodes (Araneae, Theridiidae). Bulletin of the Museum of Comparative Zoology 127 (2): 75‑204. • Fincke OM, Higgins L, Rojas E (1990) Parasitism of Nephila clavipes (Araneae, Tetragnathidae) by an ichneumonid (Hymenoptera, Polysphinctini) in Panama. Journal of Arachnology 18: 321‑329. • Gertsch W (1949) American Spiders. D. Van Nostrand Company, New York, 285 pp. • Gillung J, Borkent C (2017) Death comes on two wings: a review of dipteran natural enemies of arachnids. Journal of Arachnology 45: 1‑19. https://doi.org/10.1636/JoAS-16-085.1 • Gray MR, Anderson GJ (1989) A new Australian species of Argyrodes Simon (Araneoidea: Theridiidae) which preys on its host. Proceedings of the Linnean Society of New South Wales 111 (1): 25‑30. • Guarisco H (1999) Distributional status and natural history observations of the genus Argyrodes (Araneae: Theridiidae) in Kansas. Transactions of the Kansas Academy of Science 102 (3-4): 138‑141. https://doi.org/10.2307/3627875 • Guarisco H, Cutler B (2018) Checklist of Kansas cobweb weaving spiders. The Kansas School Naturalist 62 (3): 1‑13. • Hall GG (1937) The North and Central American spider parasites of the genus Pseudogaurex (Diptera: Chloropidae). Journal of the Washington Academy of Sciences 27: 255‑261. • Jackson RR, Cross FR (1987) A cognitive perspective on aggressive mimicry. Journal of Zoology 290 (3): 161‑171. https://doi.org/10.1111/jzo.12036 • Jackson RR, Wilcox RS (1993) Observations in nature of detouring behaviour by Portia fimbriata, a web-invading aggressive-mimic jumping spider from Queensland. Journal of Zoology 230: 135‑139. https://doi.org/10.1111/J.1469-7998.1993.TB02677.X • Kaston BJ (1970) Comparative biology of American black widow spiders. Transactions of the San Diego Society of Natural History 16 (3): 33‑82. • Larcher SF, Wise D (1985) Experimental studies of the interactions between a webinvading spider and two host species. Journal of Arachnology 13: 43‑59. • Leighton E, Miller G (1997) Host preference and temporal change in host availability of two web-invading spiders, Argyrodes trigonum and A. cancellatus. Conference abstract. American Arachnological Society 1997 Annual Meeting, 1997. Dickinson, 1 pp. 16 Cowles J, Agnarsson I • Miyashita T (2001) Competition for a limited space in kleptoparasitic Argyrodes spiders revealed by field experiments. Population Ecology 43 (1): 97‑103. https://doi.org/10.1007/ pl00012020 • Miyashita T (2002) Population dynamics of two species of kleptoparasitic spiders under different host availabilities. Journal of Arachnology 30: 31‑38. https://doi.org/ 10.1636/0161-8202(2002)030[0031:PDOTSO]2.0.CO;2 • Miyashita T, Maezono Y, Shimazaki A (2004) Silk feeding as an alternative foraging tactic in a kleptoparasitic spider under seasonally changing environments. Journal of Zoology 262 (3): 225‑229. https://doi.org/10.1017/s0952836903004540 • Pasquet A, Leborgne R, Cantarella T (1997) Opportunistic egg feeding in the kleptoparasitic spider Argyrodes gibbosus. Ethology 103: 160‑170. https://doi.org/10.1111/ j.1439-0310.1997.tb00015.x • Pett BL, Ferreira E, Agnarsson I (In Press) Megadiverse Madagascar: New species and genera of argyrodine spiders (Araneae, Theridiidae, Argyrodinae) from the eastern rainforest reserve Analamazoatra. Insect Systematics and Diversity • Pierce WD (1942) Fauna and flora of the El Segundo sand dunes. 12. Utilization of the black widow parasite, and further data on spiders and parasites. Bulletin of the Southern California Academy of Sciences 41: 14‑28. • Sierwald P, Fenzl T (1999) Argyrodes in the webs of the Floridian red widow spider (Araneae: Theridiidae). Florida Entomologist 82 (2): 359‑361. https://doi.org/ 10.2307/3496591 • Silveira MC, Japyassú H (2012) Notas sobre o comportamento da aranha cleptoparasita Argyrodes elevatus (Theridiidae, Araneae). Revista de Etologia 11 (1): 56‑67. https:// doi.org/10.22491/etologia.v11n1.art7 • Smith-Trail D (1980) Predation by Argyrodes (Theridiidae) on solitary and communal spiders. Psyche 87: 349‑355. https://doi.org/10.1155/1980/74071 • Su Y (2012) A gang of thieves: Evolution of cooperative kleptoparasitism in the subfamily Argyrodinae (Araneae: Theridiidae). D.Phil. thesis. University of Kansas, Lawrence. • Su Y, Smith DR (2014) Evolution of host use, group-living, and foraging behaviours in kleptoparasitic spiders: Molecular phylogeny of the Argyrodinae (Araneae: Theridiidae. Invertebrate Systematics 28: 415‑431. https://doi.org/10.1071/IS14010 • Tanaka K (1984) Rate of predation by a kleptoparasitic spider, Argyrodes fissifrons, upon a large host spider, Agelena limbata. Journal of Arachnology 12: 363‑367. • Triana E, Barrantes G, Hanson P (2012) Incidence of parasitoids and predators on eggs of seven species of Theridiidae (Araneae). Bulletin of the British Arachnological Society 15 (9): 293‑298. • Tso IM, Severinghaus LL (1998) Silk stealing by Argyrodes lanyuensis (Araneae: Theridiidae): a unique form of kleptoparasitism. Animal Behaviour 56 (1): 219‑225. https:// doi.org/10.1006/anbe.1998.0770 • Tso IM, Severinghaus LL (2000) Argyrodes fissifrons inhabiting webs of Cyrtophora hosts: prey size distribution and population characteristics. Zoological Studies 39 (3): 236‑242. • Vetter R, Vincent L, Itnyre A, Clarke D, Reinker K, Danielsen DR, Robinson L, Kabashima J, Rust M (2012) Predators and parasitoids of egg sacs of the widow spiders, Latrodectus geometricus and Latrodectus hesperus (Araneae: Theridiidae) in southern California. Journal of Arachnology 40 (2): 209‑214. https://doi.org/10.1636/hi11-93.1 Thieves and freeloaders: Argyrodine kleptoparasites invading cobwebs (Theridiidae) ... 17 • Vollrath F (1979a) Behaviour of the kleptoparasitic spider Argyrodes elevatus (Araneae, Theridiidae). Animal Behaviour 27: 515‑521. https://doi.org/ 10.1016/0003-3472(79)90186-6 • Vollrath F (1979b) Vibrations: Their signal function for a spider kleptoparasite. Science 205 (4411): 1149‑1151. https://doi.org/10.1126/science.205.4411.1149 • Vollrath F (1987) Kleptobiosis in spiders. In: Nentwig W (Ed.) Ecophysiology of spiders. Springer-Verlag, Berlin, 274–286 pp. https://doi.org/10.1007/978-3-642-71552-5_20 • Weng JL, Barrantes G (2007) Natural history and larval behavior of the parasitoid Zatypota petronae (Hymenoptera: Ichneumonidae). Journal of Hymenoptera Research 16 (2): 326‑335. • Whitehouse MEA (1986) The foraging behaviours of Argyrodes antipodiana (Theridiidae), a kleptoparasitic spider from New Zealand. New Zealand Journal of Zoology 13: 151‑168. https://doi.org/10.1080/03014223.1986.10422658 • Whitehouse MEA (1988) Factors influencing specificity and choice of host in Argyrodes antipodiana (Theridiidae, Araneae. Journal of Arachnology 16: 349‑355. • Whitehouse MEA, Agnarsson I, Miyashita T, Smith D, Cangialosi K, Masumoto T, Li D, Henaut Y (2002) Argyrodes: phylogeny, sociality, and interspecific interactions-a report on the Argyrodes Symposium, Badplaas. Journal of Arachnology 30: 238‑245. https:// doi.org/10.1636/0161-8202(2002)030[0238:APSAII]2.0.CO;2 • Whitehouse MEA (2011) Kleptoparasitic spiders of the subfamily Argyrodinae: a special case of behavioural plasticity. In: Herberstein M (Ed.) Spider behavior: Flexibility and versatility. Cambridge University Press, New York, 348–386 pp. https://doi.org/10.1017/ CBO9780511974496.011 • Wise DH (1982) Predation by a commensal spider, Argyrodes trigonum, upon its host: an experimental study. Journal of Arachnology 10: 111‑116. Supplementary material Suppl. material 1: Supplementary notes on natural history Authors: Jillian Cowles Data type: observations Brief description: Further notes on natural history. Download file (21.48 kb) 18 Cowles J, Agnarsson I