Nelson, X. J., R. R. Jackson, G. B. Edwards, and A. T. Barrion. 2005. Living with the enemy: jumping spiders that mimic weaver ants. The Journal of Arachnology 33:813-819.

Myrmarachne are a genus of spider that mimics ants to avoid predation by other animals. But what happens when the ants Myrmarachne is mimicking are also its predators? Can Myrmarachne still survive ant predation more often than spiders not mimicking ants?

Several Myrmarachne associate with a particular species of ant. One species of spider, Myrmarachne assimilis, is unique in that, while exhibiting Batesian mimicry (mimicking dangerous or unappetizing animals in order to deter predators), it is forced to associate with the very aggressive ant species it resembles, Oecophylla smaragdina, which can prey on Myrmarachne.

This experiment utilized different spider species that had never had previous contact with ants. Single spiders were placed in containers with ten, twenty, or forty ants and, after ten hours, the number of live spiders was counted. Spiders not mimicking ants demonstrated the lowest survival rate and, with the smaller ant groups, M. assimilis had much higher survival rates than all of the other spiders tested. However, in groups of forty ants, M. assimilis' survival rate was not notably different from that of the other ant-mimicking spiders.

Certain Myrmarachne live in close proximity to the aggressive ant model they mimic. Their mimicry, however, insures that Myrmarachne are more resistant to predation by these ant species. To conclude, Nelson et al. postulate that M. assimilis' survival rate only differs significantly from that of other ant mimics when using its model, O. smaragdina, as a predator and that several unknown adaptations could also contribute to Myrmarachne survival rates.

(250 words)

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(posted Mar. 24 2009)