Velvet Spiders

Velvet spiders (family Eresidae) are a small group (about 130 species in 9 genera) of spiders almost entirely limited to the Old World, with exception of a few species known from Brazil. The characteristics of this family of spiders are that they are entelegyne (have a genital plate in the female), eight-eyed araneomorph spiders that build unkempt webs. They are cribellate (use woolly silk). Some species are nearly eusocial, lacking only a specialized caste system and a queen. They cooperate in brood rearing, unlike most other spiders except for some African agelenid spiders in the genus Agelena and a few others.

Female velvet spiders exhibit a remarkable type maternal care unique among arachnids. Upon the birth of her brood, the mother spider liquefies her internal organs and regurgitates this material as food. Once her capability to liquefy her insides is exhausted, the young sense this and consume the mother.

The genus Penestomus was previously placed in Eresidae as the subfamily Penestominae, but was elevated to its own family, Penestomidae, in 2010.

Spiders of the genus Stegodyphus genus, such as Stegodyphus sarasinorum in India, are known for their elaborate and robust nests and their colony integrity.

Somatic morphology:Carapace subrectangular in dorsal view; cephalic region may be strongly raised. Eight eyes in two rows, posterior eye row strongly recurved so that the PLE are set far back from the others (Figs 8B, D, F, H, J, L, 9B, D, F, H, J, L, 10 B, D, F, H, J, L, 11B, D, F, H, J, L). Tapetum absent from eyes. The anterior-median part of carapace extended ventrally into a clypeal hood (Figs 8A, C, E, G, I, K, 9A, C, E, G, I, K, 10A, C, E, G, I, K, 11A, C, E, G, I, K). Two or more setal morphologies typically present appearing as dark and white setae in museum specimens (Figs 35B, 81D, 91B). Chelicerae robust, may be contiguous (Fig. 19G) or excavated mesally (Fig. 68F), distal anterior part with dense cluster of strong setae near fang (Fig. 28C), usually with boss (Figs 28B, 46B, 56E, but see 56C); large single keel anterior to fang, may be serrate, with series of small denticles leading towards base of fang; there is no distinct fang furrow (Figs 34F, 91F). Female palp with tarsal claw (Fig. 92F). Legs usually short with two rows of trichobothria on tibiae and one distal trichobothrium on metatarsi. Bothria have series of transverse grooves proximally (Figs 25D, 38B, 45E, 92B). Tarsal organ small, capsulate, and positioned near the distal tip (Figs 38A, 46D, 92A). Major and median claws with series of teeth (Figs 38C, 92C). Linear calamistrum occupies entire length of metatarsus IV (Figs 25E, 38D, 46E, 92D), with a dorsal patch of smaller calamistral setae (i.e., with lines of teeth, Figs 25F, 31F, 38E, 46F, 67F, 82F, 92E). In some eresids, the line of primary calamistrum setae is not clearly distinguishable from the dorsal patch (Figs 25F, 31F, 46F, 67F). Abdomen generally oblong with distinct dorsal sigilla (Figs 3I, 4H, 19A, 47I, 89E). Posterior respiratory system comprises four simple tracheal tubes (Lamy 1902; CEG, pers. obs. Stegodyphus and Dresserus). Male palp: Male palpal tibia without apophysis, with two rows of trichobothria (Figs 27F, 34E, 55F). Palpal bulb with sclerotized conductor that interacts with spiral embolus (Figs 27C, 34D, 41F, 90D), expansion occurs in both the basal and median haematodochae (Figs 12F, 13C, F, 15C, L). Axis of spiral typically proximal-distal with embolus encircling distal part (Figs 12B, 13B, H, J, 14I, 15B, H, K), occasionally more or less ventral-dorsal with embolus encircling ventral part (Dresserus and Gandanameno; Figs 12G, 13D, 33I–K, 48A–F). Female genitalia: Epigynum present with entelegyne configuration, one pair of spermathecae (typically in a posterior position except in Dresserus and Gandanameno, where they are anterior), and spermathecal heads (typically in an anterior position and far from the spermathecae except in Dresserus and Gandanameno, where they are adjacent to the spermathecae; Figs 16D–F, J–L, 17D–F, 18D–F, J–L, 22B, 29D, 37E, 42D, 45B, 59C, 65B, 76B, 82B, 86B, 93B); posterior lobe absent (compare Figs 45A, 93A with Miller et al. 2010b: fig. 8A). Spinneret spigot morphology: ALS typically with multiple MAP (absent in Seothyra, Figs 77B, 78B) and a field of PI (Figs 36B, 94B). PMS with one to several mAP and a field of AC, occasionally elongated and divided into two lobes (female Dresserus and Gandanameno, Figs 36C, 57A, C), CY present (Figs 36C–D, 57C, 58E) or uncertain. PLS with field of AC, MS positioned on dorsal part adjacent to ALS far from rest of field, may be accompanied by one (Dorceus, Figs 30F, 32F) or two (Eresus sandaliatus group, Loureedia gen. n., Seothyra, Stegodyphus, Figs 67D, 87D, 95E) flanking AC (no MS-flanking AC in at least Dresserus and Gandanameno, Figs 36E, 57D, 58C, 61B–C). Cribellum present with median division in most genera (Figs 57E, 77E, 87A, 94A, E), each half subdivided in Dresserus (Fig. 36F). Multiple epiandrous gland spigots present in male (Figs 22E–F, 28D, 39F, 45F, 61E–F, 65F, 74E–F, 80E–F, 85E–F, 93F).