This winter I purchased a copy of A Field Guide to the Ants of New England, a beautiful book by multiple authors published by Yale (I know I’m in Minnesota but a lot of the species overlap, and the general information in this book would be hard to top). So this spring, as the ants have begun to reappear around the yard, I’ve made a point of collecting specimens, chilling them in the refrigerator, examining them under the microscope, familiarizing myself with the keys, both dichotomous and matrix, and some of the local fauna. And while I’ve made some progress in my knowledge of the ants, it’s increasingly obvious that I have a long, long way to go.
For instance, yesterday, returning home from some errand, I noticed a small ant on the side of the house and noticed, also, that it had pale legs. I’d read in the guidebook about the Somewhat Silky Ant (Formica subsericea), the males of this species having distinctively yellow legs, so I thought it worth my while to find a vial and collect this ant. A few hours later, I took the vial out of the refrigerator and examined the ant under the microscope. Only it wasn’t an ant! It was a spider!
A quick Boolean search online for “ant-mimic” and “spider” brought me to the bugguide.net page for the spider Synemosyna formica. The mimicry exhibited by this spider is astonishing. Not only does the shape of this spider closely match that of an ant, but it’s two front legs, darker than the other six, are held out in front as it walks to resemble antennae. And it ambles exactly like an ant, not a spider, and certainly not like a jumping spider to which family it belongs. Going back to the guidebook, I found the section on ant-mimicry, a picture of this very species, and an account very similar to my own: “We once collected one of these spiders, Synemosyna formica, in a Maine bog. Until we returned it to the laboratory and put the specimen under a dissecting microscope, we were sure it was a bog ant (Myrmica lobifrons)!” An easy mistake to make with this spider.