In the dank forests along the Pacific coast there can be found a leggy little creature, scarcely two inches in length, crawling among the sodden leaf litter and pine needles and mossy, moldering woodrot at a methodical plod. Its elongate form is clearly arthropodal; closer inspection reveals roughly twenty shining segments, each painted an aposematic yellow and black. Thirty-odd pairs of legs undulate along the span of its body, starting from the rear and rippling toward the head in a locomotive wave. Its movements are the can-can in slow motion, thirty kicking limbs on either side. The millipede chugs along, unhurried and unafraid.
Whence arises its nonchalance, its poise? The yellow-spotted millipede (Harpaphe haydeniana) is a denizen of the forest floor, a decomposer par excellence. It consumes dead plant matter and expedites the leaf litter’s decay, breaking down cellulose and lignin in its gut and excreting ready-to-use fertilizer in its wake. Like earthworms, the millipedes provide an immeasurable benefit to the health of the forest, aerating soil, cycling nutrients, and generally keeping plant waste at a manageable level. Unlike earthworms, however, the yellow-spotted millipede has a toxic leg-up: when threatened, it emits sweet-smelling hydrogen cyanide from its sides, in a dose powerful enough to deter shrews and beetles and most other smallish predators. The cyanide is redolent of almonds, hence the common names “almond-scented millipede” or “cyanide millipede” for the oft-encountered critter.
Springtime is mating time for many animals, millipedes included. Their nuptials are announced via sex pheromone, secreted by the female and tracked slowly but fervently by the male. Courtship typically involves a male mounting a female—that is, literally standing on top of her, stacked like a double-decker bus—and massaging her sides with his legs, a rhythmic, sixty-footed caress. If performed satisfactorily, he’s allowed to pass a sperm packet to her, which she stores for later fertilization. Sometimes, in a sort of sylvan orgiastic frenzy, tens of thousands of millipedes will congress (in multiple senses of the word) in a writhing, almond-scented mass on the forest floor, blinded by pheromonal haze. There are millipedes massaging millipedes, left and right, up, down, all around—impossible to tell who’s caressing whom. Lots of legwork going on, that much is clear.
As a dutiful detritivore, eating and pooping and decomposing, yellow-spotted millipedes are integral to Pacific Northwest forest ecology, says Oregon State University researcher Andy Moldenke. The forest depends on them as surely as the rain. “From a conservation point of view, they’re absolutely critical,” he says. So give yourselves a hand, millipedes (or a leg, or thirty legs, or whatever).