Smells Like Almonds

Cyanide-producing Millipede (Harpaphe haydeniana)
The yellow spots on black make the Cyanide-producing Millipede (Harpaphe haydeniana) easy to identify.

I’m always on the lookout for the small and interesting while walking in the forests of Vancouver Island. While at Seal Bay Regional Park near Comox, British Columbia this week I came across a large yellow-spotted black millipede crossing the trail.

I’ve seen these Cyanide-producing Millipedes (Harpaphe haydeniana) countless times in the forest and have always been fascinated by them. They are a large, easy to identify millipede due to their size and colour. In addition, when handled they curl into a defensive spiral and give off a strong odor that smells like almonds – this smell is the stuff of Agatha Christie – cyanide!

According to Andrew Moldenke, a Research Associate in Entomology, Department of Entomology, Oregon State University, the odor of roasted almonds is actually hydrogen cyanide gas, a potent metabolic poison. As a result, H. haydeniana has only one predator, the groundbeetle Promecognathus laevissimus. Fortunately, this means that the millipede can perform its duty as a “macroshredder,” breaking up plant material and initiating the process of nutrient recyclying in the soil ecosystem without having to worry about a whole host of predators. In fact, it plays such an important role in the process that it can be considered to be a “keystone” species.

The quote below is attributed to Moldenke (I couldn’t find the original link but part of it is similar to a paper authored by Moldenke called Soil-Dwelling Arthropods: Their Diversity and Functional Roles which was presented at a Pacific Northwest Forest and Rangeland Soil Organism Symposium, 1998)

Throughout Northwest forests, the principal shredder is the cyanide-producing millipede (Harpaphe haydeniana), which has a shining black body and bright orange racing stripes. Since the millipede crushes, filters and then recrushes its dead leaf diet, it increases the availability of nutrients 40,000-fold. After extracting what it needs, the millipede defecates a pellet of partially used nutrients covered with microbial fuel (intestinal mucus). Immediately, a microbial garden grows on the surface and then a soil fungivore comes along and breaks up the pellet, feeds, excretes with its own mucus, and the whole process repeats over and over again until all the nutrients are used up. It is the shredder that is key to the process. The cyanide-producing millipede alone eats 33 to 50 percent of all the dead coniferous and deciduous leaves that come to rest on the forest floor. It is one of the most critical links in the entire soil foodweb.

Andrew Moldenke

Cyanide-producing Millipede (Harpaphe haydeniana)
The Cyanide-producing Millipede (Harpaphe haydeniana) is a key macroshredder in the Pacific Northwest.

As we celebrate Earth Day around the globe it is important to think about the roles that the smaller, often missed, organisms play in the ecosystems that we all are part of. I know that I’ll look at this beautiful millipede a little differently the next time I see it.

If you’ve enjoyed this post you might want to check out the Circus of the Spineless, hosted this month by Arthropoda, for more invertebrate goodness.

Circus of the Spineless