Nyffeler et al. (1990) published an extensive review on spiders as egg predators, which led to the conclusion that spiders frequently feed on lepidopteran and spider eggs and very rarely on coleopteran eggs. This study inspired many other researchers to follow up on this topic (e.g., Ruberson & Greenstone 1998; Miliczky & Calkins 2002; Pfannenstiel 2008; Myers et al. 2020). Three decades later, we conducted an update on this topic, revealing that oophagy in spiders is much more widespread and diverse than previously anticipated (Table 1). The update is based on 233 reports, 130 (56%) of which were not included in the Nyffeler et al. (1990) paper (see   Supplemental Table S1 (arac-50-01-07_s01.pdf), online at  https://doi.org/10.1636/JoA-S-21-016.s1). In the following, we report this additional information.

Table 1.

List of egg taxa reported to be consumed by spiders based on a literature survey (n = 233 reports; see  Supplementary material (arac-50-01-07_s01.pdf) for a complete list of all reports).

Roughly 75% of the reports referred to the consumption of lepidopteran and spider eggs (Table 1; Figs. 1A-D). Less frequently, instances of feeding on the eggs of coleopterans, dermapterans, dipterans, heteropterans, homopterans, hymenopterans, acarids, neuropterans, and opilionids were reported in the literature (Table 1; Figs. 2A-B). Spider predation on arthropod eggs has been reported from all continents except Antarctica (see  Table S1 (arac-50-01-07_s01.pdf)).

Figure 1.

Salticid spiders consuming arthropod eggs. (A) Portia fimbriata (Doleschall, 1859), eating the eggs of a defeated conspecific female in Queensland, Australia (Photo copyright: Mark Moffett). (B) Pelegrina cf. aeneola (Curtis, 1892) consuming eggs of a noctuid moth (presumably Xylena cineritia) in Montana, USA (Photo by Glenn Marangelo). (C) Thyene coccineovittata (Simon, 1886) feeding on the egg of a pentatomid bug on a Ficus tree in Rio de Janeiro, Brazil (Photo by Laíza Mussap Cukier). In another photo, presented by Cukier (2020), punctured eggs whose internal contents had been sucked out by the spider can be seen. (D) Unidentified jumping spider (Opisthoncus L. Koch, 1880) consuming eggs of the Bronze orange bug Musgraveia sulciventris (Tessaratomidae) in Queensland, Australia (Photo by Ron Atkinson). On the left side of the picture, three empty eggshells – a clear indication of the feeding activity performed by the jumping spider – can be seen.

Figure 2.

(A) Juvenile Osoriella rubella (Keyserling, 1891) (Anyphaenidae) consuming an egg of the harvestman Iporangaia pustulosa (Gonyleptidae) near Sao Paulo, Brazil (Photo by Gustavo S. Requena). (B) Parasteatoda tepidariorum spider (Theridiidae) lassoed lacewing eggs (Chrysopidae) with its web and then started eating them as they hatched; picture taken in Airlie Beach, Queensland (Photo Steve & Alison Pearson).

Not only do spiders feed on arthropod eggs, the natural diets of various spider groups also include vertebrate eggs (Table 1; Fig. 3). The third most common type of oophagy referred to spiders devouring anuran eggs/embryos (23 in 233 reports). This type of oophagy referred for the most part to predation upon embryos of about a dozen different glass frog species (Centrolenidae) in Central and South America (Figs. 3A-B; Rojas-Morales & Escobar-Lasso 2013; Valencia-Aguilar et al. 2012, 2020, 2021; and others). In addition, feeding on frog eggs/embryos has now been documented from several other anuran families (Table 1) and must be placed in a broader context with anurophagy in spiders (see Nyffeler & Altig 2020). Finally, a report from Sri Lanka documents spider predation on lizard eggs (Squamata; Priyadarshana & Wijewardana 2016). In this latter case, an unidentified huntsman spider, Heteropoda Latreille, 1804 (Sparassidae) killed an adult female Common House Gecko (Hemidactylus frenatus Duméril & Bibron, 1836) and, after 14 hours, the gecko was totally consumed, along with its eggs (Fig. 3C).

Figure 3.

Spiders consuming vertebrate eggs. (A) Juvenile wandering spider Cupiennius getazi Simon, 1891 (Trechaleidae) near an egg clutch of the glass frog Agalychis callidryas (Centrolenidae) is consuming one of the embryos. The incident was witnessed in Costa Rica (Photo by Peter van Zandt). (B) Unidentified wandering spider, Cupiennius Simon, 1891 (Trechaleidae) devouring eggs of an unidentified glass frog (Centrolenidae) in the Manduriacu Reserve, Ecuador (Photo copyright: Jaime Culebras). (C) Spider Heteropoda sp. (Sparassidae) feeding on an immature egg of the gecko Hemidactylus frenatus in Sri Lanka (Photo by Tharaka Sudesh Priyadarshana & Ishara Harshajith Wijewardana).

Eggs are singly deposited or laid in clutches (such an egg mass is defined as a group of eggs layed simultaneously in close proximy). There are few records of attacks on single eggs. Such rare attacks on singly deposited eggs had been reported for monarch butterflies, swallowtail butterflies, and lacewings (Suwarno 2010; Hermann et al. 2019; Mezőfi et al. 2020). When attacking egg masses, the spiders usually consumed several eggs in a row (Ron Atkinson, pers. comm.; Suwarno 2010; Ahmed et al. 2018; Marangelo 2019; Cukier 2020; and others). It appears that mostly unguarded egg masses were attacked by spiders (e.g., Pasquet et al. 1997; Buzatto et al. 2007; Jackson et al. 2008; Guayasamin et al. 2019).

As oopghagy in spiders is widespread, the question arises whether specific adaptations for oophagy are known in this predator group. Such adaptations are indeed known as regards the consumption of spider eggs. Firstly, the web-building spider Amaurobius ferox (Walckenaer, 1830) (Amaurobiidae) produces “trophic eggs,” which means that the mother provides non-developing eggs for its freshly hatched offspring to eat (Kim & Roland 2000). This reproductive strategy markedly increases the survival probability of the offspring of this spider species. Secondly, in some species of the ant-mimicking jumping spiders in the genus Myrmarachne MacLeay, 1839, males have strikingly enlarged chelicerae that make them highly efficient in opening other spiders' silken retreats and eating their eggs after invading alien webs (Jackson & Willey 1994). This is likely a case of morphological adaptation for oophagy. Thirdly, Jackson and colleagues have shown in a series of papers that numerous salticid species habitually invade alien webs to steal prey (kleptoparasitism) and eat the resident spider as well as its eggs (Fig. 1A; Jackson & Pollard 1996; Cerveira et al. 2003). In these cases, web invasion followed by eating the resident spiders’ eggs is one of the diverse predatory strategies employed by the salticids (Jackson & Pollard 1996). The same behavior of web invasion coupled with kleptoparasitism, araneophagy, and oophagy was also observed in several other spider families (Jackson & Whitehouse 1986; Jarman & Jackson 1986; Cerveira & Jackson 2005). Invasion of alien webs followed by oophagy can be very rewarding, as shown by the example of the salticid Phyaces comosus Simon, 1902, which invades the webs of much larger salticids (Jackson 1986). As a case in point, a P. comosus invading the web of the salticid Bavia aericeps Simon, 1877, is able to eat a single egg almost as large as itself. As Jackson (1986) wrote, “....the egg mass in a single egg sac is a veritable bonanza.”

What specific adaptations for oophagy are known by spiders in which consumption of insect eggs is concerned? Several salticid species have been reported to feed on ant eggs after entering the ants' nests (Nelson & Jackson 2009a; Cushing 2012). The fact that the spiders were able to feed on ant eggs unhindered by the ants implies that the spiders in question must be chemically disguised so that the ants could not recognize them as foreign intruders (Nelson & Jackson 2009a; Parmentier et al. 2015). In the case of the salticid Cosmophasis bitaeniata (Keyserling, 1882), spiders acquire the ants' odor through the consumption of ant larvae (Elgar & Allan 2004); this would be classified as a case of behavioral adaptation. In many other cases eating insect eggs appears to be largely an occasional, opportunistic occurence (David Hill, pers. comm.). But such cases of opportunistic feeding are limited to a large extent to a group of “active searchers” equipped with the sensory systems needed for the detection and identification of immobile prey such as eggs (see Nelson & Jackson 2009b; Gallagher et al. 2013). In particular, Anyphaenidae, Cheiracanthiidae, Oxyopidae, and Salticidae are known to opportunistically feed on insect eggs (Table 1). These same spider groups are also occasionally seen feeding on other immobile food such as various types of plant matter (Nyffeler et al. 2016).

How does oophagy affect the food supply of spiders? So far very few quantitative assessments of eggs as spider prey exist. In two studies on the natural diets of salticids, insect eggs made up ≈2–4% of the spiders' total prey (Zabka & Kovac 1996; Guseinov et al. 2004), while in other studies insect eggs seem to have been absent in the diets of salticids (e.g., Jackson 1977; Edwards 1980). Thus, predation on insect eggs appears to contribute rather insignificantly to the annual food supply of jumping spider populations. Nevertheless, if we look at it from the point of view of a single individual, opportunistically feeding on an insect egg mass may be quite rewarding for an individual. In studies on the natural diets of two other cursorial hunters – an unidentified palpimanid (Palpimanus Dufour, 1820) and a salticid (Myrmarachne melanotarsa Wesołowska & Salm, 2002) – spider eggs composed 13–17% of the total prey (Cerveira & Jackson 2005; Jackson et al. 2008). Feeding on spider eggs therefore appears to be rewarding for araneophagic spiders that habitually invade alien webs.

In conclusion, the significance of oophagy for the food supply of spiders appears to vary considerably depending on the species of spider in question. The use of eggs as a supplementary food source represents an opportunity to enlarge the spiders' food base, which might be of nutritional significance most notably during periods of food scarcity. Oophagy becomes even more meaningful considering that arthropod eggs and vertebrate eggs are high quality prey due to their high protein content (Eubanks & Denno 2000; Neckel-Oliveira & Wachlevski 2004).