I don’t recall ever seeing one of these little millipedes before, but it’s probably just that I never paid attention. These small millipedes in the order Polyxenida never measure more than 4mm based on everything I’ve just read. The only reason I recognized this one was because of a recent appearance in one of Ted C. MacRae’s identification challenges. This one was found crawling around in the soil beneath a log.
Unfortunately I didn’t get as good a photo as I had hoped. Not a single one had the whole critter in focus. The head is to the right, by the way. You can make out the antennae and what look kinda like compound eyes, but are actually just a grouping of ocelli.
In at least one species of these millipedes, it has been shown that the tufts of bristles on the rear defend against attack by ants. The barbed bristles detach easily, entangling, distracting, and in some cases fatally disabling the predator. Read more about this strategy and check out some neat images and micrographs at the link below.
Proc. Natl. Acad. Sci. USA
Vol. 93, pp. 10848-10851, October 1996
Millipede defense: Use of detachable bristles to entangle ants
Thomas Eisner, Maris Eisner, and Mark Deyrup