Millipedes

by Kim Woolcock

It’s spring, and all kinds of creatures are crawling out from under the leaf litter. Including millipedes.

Their name means “thousand legs” (even though only one millipede, Eumillipes persephone, has more than a thousand legs, and it was just discovered in December 2021). Despite their many legs, they are not fast runners, and they cannot bite or sting. To prevent becoming tasty snacks, they have many defenses. The most well-known is their ability to curl into spirals, with their head in the middle.

Coiled Millipede in dry leaf litter
Taken by: Prosthetic Head

Some carry physical weapons. Polyxenid millipedes have interlocking bristles on their butt that they rub off on ants. The bristles get stuck on the ants, who give up attacking the millipede to remove the bristles. The bristles, which are barbed and have grappling hooks at the end, interlock as the ant tries to get them off. Some ants are too entangled to remove them, and die.

Polyxenus lagurus (Diplopoda, Polyxenida). Dundon, England, United Kingdom
Taken by: Andy Murray

But most millipedes carry chemical weapons, stored in the aptly named “repugnatorial glands." Millipedes can produce eight major types of repellent chemicals, from phenols to quinones to hydrogen cyanide (yes, cyanide).

When threatened, some millipedes squeeze muscles around their repugnatorial glands [editor's note: these are glands that drive away predators], dotting their backs with droplets of predator repellent. Others just let their defensive chemicals ooze out and coat their exoskeleton. But some can spray their repellent, up to 50 cm! Large millipedes from Hispaniola are reported to be able to blind chickens. Others, like Glomeris marginata, take a different tack, exuding a sedative similar to Quaalude, which can put wolf spiders to sleep (it also tastes terrible and it’s not known if predators ingest enough to actually fall asleep or if they’re just put off by the bad taste). Just in case, G. marginata includes sticky proteins in its secretions, entangling its would-be predators.

Flat-backed millipedes don’t mess around with bad tastes or smells—they produce hydrogen cyanide. Yes, cyanide, the famously fast-acting, potent poison. Millipedes are immune to it, and they can exude enough to kill birds and mice. Some of these cyanide producers, like Harpaphe haydeniana, are so deadly they have basically only one predator, the beetle Promecognathus laevissimus, which is also immune to cyanide.

Harpaphe haydeniana
Taken by: Franco Folini

All of this makes them sound rather menacing. But down there on the forest floor, protected by their chemical arsenal, they are performing an essential service: they are shredding up the leaf litter, grinding it into tiny pieces and making the nutrients more available for the rest of the food web. A study of the yellow-spotted millipede in BC’s coastal rainforest estimated that it consumes 36% of the annual coniferous litterfall. Just that one species! That is a lot of shredding.

To learn more about tiny creatures and their superpowers, check out my new book It’s Tough to be Tiny, coming out from Flying Eye Books in September, illustrated by Stacey Thomas. It’s full of fun facts about creatures like springtails and cone snails and how they evade predators, hunt for their lunch, and buddy up with bigger creatures for the benefit of both.

Resources
https://www.sciencenews.org/article/millipede-most-legs-eumillipes-persephone
https://blog.nature.org/science/2017/10/17/millipede-protects-itself-cyanide-yellow-spotted-bugs/
https://www.nature.com/articles/s41598-018-19996-6
https://www.pnas.org/doi/full/10.1073/pnas.1500014112
https://www.sciencedirect.com/science/article/pii/S0305197815001167
https://www.loc.gov/everyday-mysteries/zoology/item/how-are-millipedes-and-centipedes-alike-and-how-do-they-differ/
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC38244/
https://cdnsciencepub.com/doi/10.1139/x00-014