The velvet spiders (family Eresidae) are a small group (about 100 species in 10 genera) of almost totally Old World spiders (exception: a few species are 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. With the exception of Wajane, they are cribellate (use wooly silk). Some species are nearly eusocial, lacking only a specialized caste system and a queen. They cooperate in brood rearing, unlike almost most other spiders except for some African agelenid spiders in the genus Agelena and a few others.
Myrmarachne melanotarsa, the dark-footed ant-spider, is an African jumping spider found around Lake Victoria in Africa. Like other spiders in the genus Myrmarachne, these spiders mimic ants, in this case, ants of the Crematogaster genus. However, they are unusual in that they exhibit some form of social behavior, forming clusters of silk nests on fig and other trees. Hundreds of these spiders, of both sexes and of all ages, can be found in such communal nests, but most nests have between 10 and 50 spiders. The Crematogaster ants which they mimic are often found in the nests with the spiders, along with other species of jumping spider.
Some predators (including larger jumping spiders) eat jumping spiders but are averse to attacking ants, as ants aggressively defend themselves. M. melanotarsa takes advantage of this aversion by mimicking the ants. Spiders of the genera Menemerus and Pseudicius have been shown to flee, leaving their eggs behind, when in the presence of groups of M. melanotarsa. M. melanotarsa is known to eat the eggs of such spiders. However, individuals or small groups of M. melanotarsa may be attacked and eaten by these predators who fear large groups.
Evarcha culicivora is a species of jumping spider from Kenya. It feeds mainly on the mosquito species Anopheles gambiae, the main vector of malaria in the region.
It is the only known animal that selects its prey based on what the latter has eaten. Although jumping spiders are known to rely on their excellent vision, it was shown that this species selects blood-filled mosquitos more often than unfed ones, even more so when only relying on smell (90%, as opposed to 83%): when it came to making a choice based on smell alone, with the two meal options hidden from view, around 90 percent of E. culicivora selected the blood-filled mosquito. However, it seems to select its preferred species by its resting posture, as different kinds of mosquitoes sit in different angles. This has been shown with 3D-animations of different resting postures.
In 2009 it was found that feeding on blood-filled mosquitos changes the smell of E. culicivora, leading specimens to find potential mates more attractive after a blood meal. The species is only known around Lake Victoria in Kenya and Uganda.