male Mallinella fulvipes female Mallinella shimojanai
Ant spiders are members of the family Zodariidae. They are small to medium-sized eight-eyed spiders found world-wide in tropical to warm temperate regions, though there are relatively few species in North America.
Some zodariids are ant mimics. Although ant mimicry is quite common in spiders, the form it takes in the zodariids is unusual because, although each species bears a morphological resemblance to the species of ant that forms its prey, the resemblance is not particularly close. It is enhanced by the spider's behaviour. The spiders live in association with a nest of ants of their prey species, and use their mimicry to enter and leave the nest unmolested (if the ants detected them as intruders they would mass to repel and perhaps kill them). The spiders walk on only the three rear pairs of legs, and if they encounter an ant during their forays into the nest territory, they touch their front legs to the ant's antennae in the same way as another ant would with its own antennae. If they have already captured an ant, they then offer that towards the challenging ant, which inspects it and behaves towards the spider as if it were another ant carrying a dead conspecific away from the nest (a common behaviour among ants).
It is likely that the spiders also derive some protection against predation from their similarity to the ants, since ants are unpalatable to many species that eat spiders.