Category Archives: Millipedes

Horror from within

The rains have brought all kinds of strangeness to the woods. As we wrapped up our surveys of stream salamanders, a cry went up: nematomorph! (Yes, this is an advanced class; in Introductory Biology the cry would have been, OMG-gross…) Lying on the stream bed was half of a Narceus millipede with a long white worm writhing its way out of the broken body. The millipede’s front legs were still grasping feebly at the ground. It had dragged itself several feet to this spot, leaving its other half discarded on the wet rocks.

This individual was not alone. Barely ten minutes later we found another, this time with both halves still encasing the emerging parasite.

I’m fairly confident that the students’ identification of the cause of this distress was correct: a nematomorph worm emerging from its host. However, the light color of the worm makes me a little suspicious that a mermithid nematode might also be the culprit. My search of the scientific literature revealed nothing about either of these worms in this particular host, so we may have stumbled into new corner of the vast wonderland of pain that is animal parasitism. We’ll likely head back down into Shakerag Hollow to see if we can find more worms to bring back to the lab.

Nematomorphs appear in the first chapter of The Forest Unseen as examples of one extreme of the continuum between cooperation and conflict. The worms eat their hosts from the inside out, with no regard for the comfort of the suffering victim. The vital organs are left in place to allow the host to continue feeding (the food goes mostly to the inner pirate, of course). At last the parasite directs its hollowed-out victim to water. There the worm breaks free, discards its dying carrier and squirms away to look for a mate.

After one of my recent public lectures, someone recently asked me for an example of what I meant by the “weight of the world’s pain” (what a blessed life the questioner must have led). This species could surely serve as an answer.

Some visceral fears are tapped when we observe the emergence from within of a life-robbing villain. I think these fears may, in part, be rooted in our species’ long history with parasites, some of which do indeed emerge through our flesh, others merely use existing exit orifices. Either way, we recoil in horror. Movie-makers titillate these deep-seated fears when they show slick-bodied monsters sliding out of our skin. And Freud et al‘s ideas of the unconscious are so successful because of our pre-existing and, ahem, unconscious fear of what might be hidden within us (oh delicious infolding circularity). Psychoanalysis entices because it promises to draw out the appalling inner worm, a cleansing that is surely the deep desire of all animals.

Narceus millipede, with mites

Look closely at this Narceus millipede and you’ll see two small hitch-hikers (one near the center of the  coil and one at opposite end of the millipede). These mites have a very close relationship with their millipede host.

Narceus millipedes live on and in dead logs. At this time of year, they gather together in writhing mating tangles. Because the adult mites never wander away from their millipede, this is their only chance to meet other mites, so they also breed now, having synchronized their life-cycle to that of their host. Both millipede and mite will then overwinter buried in logs or the soil. In spring, both species lay eggs in millipede frass (dung) in logs; the eggs hatch out together.

The millipedes and mites live for several years. Millipedes feed on fungi and dead wood. Adult mites feed on exudations from the millipedes’ bodies. Young mites wait for millipedes to hide from the sun inside a log, then wander off the host to feed on small invertebrates.

This whole family of mites, the Heterozerconidae, live exclusively on millipedes.

For more info, see: Gerdeman and Garcia (2010).  Heterozerconidae: A comparison between a temperate and a tropical species. Trends in Arachology.