Ant Mimicking Spider

As I was photographing Camponotus Ants Tending Aphids I saw a lonely ant like insect moving around on the adjacent sugar cane leaf. On close inspection it was an arthropod having 4 pairs of legs, unlike ants who possess 3 pairs. So it was not an ant but an ant mimicking spider belonging to Myrmarachne genus. Myrmarachne are type of jumping spiders of family Salticidae which have adapted Batesian mimcry and imitate an ant. They look strikingly like ants. This spider was moving very fast on that leaf, sometimes hiding behind the leaf & popping out once a while. As it was very fast in moving it gave me a hard time photographing. I photographed it using my Canon EOS 5D Mark III with Canon EF 100mm f/2.8L Macro IS USM and Canon MT-24EX macro twin light flash.

Name Myrmarachne is derived from greek word myrmex means ant and arachne meaning spider. By mimicking the ants they are able to stay close to ants and gain protection from predators who are afraid of ants. They have also adapted the zig zag movement like ants. These jumping-spiders jump only when their safety is threatened. Some scientists believe that by mimicking ants, the spiders deceive their ant-models and prey either on the ants themselves, or on the homopteran bugs “tended” by the ants like the aphids. However, it should be noted that the ant-mimicking spiders have never been observed to have attacked the ants they imitate. A more plausible explanation is that by copying the physical appearance of ants, the ant-mimicking spiders are actually buying insurance for self-protection, since spider-hunting wasps, birds and other spider-predators generally avoid ants which secrete the distasteful formic acid when attacked.

Ant-mimicry in arthropods is widespread mainly in spiders especially in families such as the Salticidae and the Clubionidae. Batesian ant mimics must live in sympatry with their models, resembling their noxious or aggressive model thereby deceiving potential predators and thus gaining protection. The resemblance of Batesian mimics of ants to their models can be both morphological and behavioral. A constriction in the middle of the carapace and a shiny opisthosoma shaped similarly to the ant’s abdomen are some of the body changes developed by these of ant-mimicking spiders. The constricted carapace gives the spider the appearance of a three-segmented body like that of ants, whereas the shiny look of the opisthosoma – obtained through the presence of specialized or scale-like setae – and its shape further increase the mimic’s resemblance to the ant.

Ant mimicking spiders often reinforce their morphological re-semblance to ants through ant-like behaviors. These behaviors include walking in a zig-zag motion, moving their opisthosoma up and down in a manner similar to gaster bobbing in ants, and waving their first pair of legs in the air while walking on the remaining three pairs. This movement of the first pair of legs in ant mimicking spiders is generally thought of as behavioral mimicry, and has therefore been termed antennal illusion. In some cases however, this leg movement is carried out by spiders to detect chemical cues from ants, as in the ant-eating zodariid spider Habronestes bradleyi.

Living like ants has changed the behaviors of these jumping spiders. Predatory sequences were found to differ considerably from the typical of jumping spiders. Instead of stalking and leaping on prey, Myrmarachne lunged at prey from close range. Myrmarachne used its first pair of legs to tap prey before lunging, another unusual behavior for a salticid. Also, Myrmarachne tends to open up, or enter into, other spiders’ nests and eat other spiders’ eggs. Myrmarachne tend to use webs of other spiders as nest sites, but no evidence was found of Myrmarachne preying on spiders in webs. It appears that the unusual features of Myrmarachne‘s predatory and nesting behavior are important in enabling these spiders to preserve their ant-like appearance.

Myrmarachne species live close to their model ant species, yet they avoid making contact with the ants. However, contact can be unavoidable at times, so the question is what really happens when the ant and the spider make contact. The most common form of contact was between the ant’s antennae and the spider’s first pair of legs. This resulted most frequently in the Myrmarachne running away. In contrast, when the spider’s chelicerae were involved the ant would usually run away. So even when there is contact between the two, Myrmarachne manages to avoid being attacked by the ant, thus remaining safe.