Brief SummaryRead full entry
The spider family Amaurobiidae (hackledmesh weavers) has a worldwide distribution and as of 2013 included 285 described species (Platnick 2013), 71 of which occur in North America north of Mexico, with a large fraction of these found in California (Bradley 2013). The genera Wadotes (Muma 1947; Bennett 1987; Wang 2002) and Coras (Muma 1946; Wang 2002) were moved from Agelenidae to Amaurobiidae in 1986, but molecular phylogenetic analyses by Miller et al. (2010) concluded that these two genera fall within the Agelenidae, as originally believed (see Wang 2002 and Ubick 2005 for a review of the taxonomic history of Amaurobiidae).
The larger amaurobiids are relatively robust, compact, and generally dark brown in color. The chelicerae (the spider's main mouthparts) are typically large and thick with a conspicuous boss (a reinforced area at the edge of the cheliceral base where it meets the cephalothorax). The North American species (with Wadotes and Coras excluded from the family) are cribellate (i.e., they have a cribellum and produce cribellate silk) and spin tangled webs with one or more funnel-shaped entrances. The messy cribellate strands of these webs are often conspicuous. Most amaurobiid species build their webs among (and hide under) rocks, logs, or decomposing material on the ground.
The number and arrangement of a spider's eyes are often helpful in determining to which family it belongs. Most amaurobiids have eight eyes in two transverse (side-to-side) rows, but the two anterior median eyes are often reduced in size or even absent.
Two striking forms of maternal investment have been studied in Amaurobius ferox, a European species that is now also established in the northeastern United States and can sometimes be found in basements. A day after the emergence of her 80 to 100 spiderlings, the new mother produces a second batch of eggs (non-fertile "trophic eggs") which are immediately devoured by her young. Three to four days later, the spiderlings undergo their first post emergence moult. The day after that, the mother is eaten by her brood. Thus, the female both invests in trophic eggs that serve to give her offspring a nutritional boost—and then goes one step further as her spiderlings consume her as well (Kim and Horel 1998; Kim and Roland 2000; Kim et al. 2000).
(Bennett and Ubick 2005; Bradley 2013)