I THOUGHT IT WAS A FOOT-LONG STRAND of twine, except that it was moving, arching upward from the doormat again and again. What in the world? On that damp December day, I met my first nematomorph (above)—an ancient sister group to the nematodes capable of turning crickets into zombies that probably has some role in the bigger picture of insect control. I learned all that after a Google search for “thin worm” led me to the work of Ben Hanelt of the University of New Mexico, and the parasitic “horsehair worms” he’s wondered about since high school, and devotes his distinguished career to the study of. Ready for a stranger-than-truth tale of science fact and fiction? (And don’t panic—they have no interest in you or your pets.)
Hanelt’s the guy who gets calls not just from curious types like me, but like clockwork from Oklahoma at the time of the first spring rain every year, when people find him to ask why their driveways are suddenly covered in the creatures, which can be a meters long (in some species) but are skinny like angel-hair pasta.
“Something odd has to happen for hairworms to be on soil or vegetation, instead of in water, so at first when I got those calls I thought: It must be earthworms,” says Hanelt, a Research Assistant Professor with the Center for Evolutionary and Theoretical Immunology in the Department of Biology at the University of New Mexico in Albuquerque. “But I asked one caller to send me some—and lo and behold, they were hairworms.”
It took years between the time Hanelt saw his first nematomorph, while on a survival-training hike in high school, until he actually knew what it was.
“There they were out in the middle of the forest in winter, in a bucket of water,” he recalls. He saved the strange animal, in a vial. Through high school and into the start of college, nobody could ID it for Hanelt—until one day: Score! It was in the Phylum Nematomorpha, and specifically a freshwater species or gordiid that parasitizes terrestrial arthropods. (He’d later learn that there are also marine species, or nectonematids, that use crustaceans as their hosts.)
He figured there would be no way to get a job that involved something so obscure, but “they kept calling my name,” Hanelt says (which I suspect is a sort of insider hairworm humor, since nematomorphs have no mouths, but actually absorb proteins and sugars through their bodies).
Eventually, when Hanelt began his Ph.D., his adviser asked what he wanted to do his thesis on. “Almost without thinking, I said nematomorphs,” he recalls, “since after all, science is the study of stuff that’s never been studied before, so why not?”
But why bother? I mean, this is not exactly some cuddly creature. Here’s the thing: It’s a case of what the eminent biologist E.O. Wilson refers to as being alert to the importance of “the little things that run the world,” invertebrates whose purpose we don’t know, but as climate and habitats change that may be lost before we find out.
“Especially with parasites, who will be lost forever if their hosts disappear, it’s urgent that we do this right now,” says Hanelt, who with his Hairworm Diversity Study colleagues Matt Bolek at Oklahoma State and Andreas Schmidt-Rhaesa at the University of Hamburg in Germany, is working to identify hairworm species worldwide. (More on their mission here.)
With the hairworms, says Hanelt, they can be frozen for up to a decade until host populations are potentially restored. Amazing.
the impressive hairworm lifecycle
WHAT HAPPENS within the host crickets (or roaches, beetles, mantids, or grasshoppers for instance): The hairworm (as larvae) gets inside them and castrates the insect—hence the inference by scientists that the parasite plays a role in insect population control. For 28 days, they live off the host, hidden away and growing into a worm.
And then things really get strange.
“Then they turn dark-colored, and start zombifying the cricket, making it move toward water and jump in,” says Hanelt. In case you are not clear: Crickets and other host insects don’t normally elect to go for a swim. “Very few parasites can turn their hosts into a zombie, but this is one.”
Eggs are laid in the water, and drop to the bottom, where larvae hatch—which in turn hitch a ride up out of the water again inside insect larvae (such as mosquitoes or crane flies) that are busy hatching on the bottom, too. Opportunists indeed!
Which brings me back to this:
So why was my hairworm on the doormat, not in the nearby water garden in my backyard?
“Do you have a light on at night near the mat?” Hanelt asked. And yes, I do.
“Well, we know that crickets, for instance, get about 80 percent of their calories each day from dead insects,” he said. “And what’s happening is that the insects that were infected as larvae in your water garden are coming to your light at night, living their life there, and then dying—and then getting ingested by a cricket.”
And the cycles repeats itself; nature wastes nothing—not an ounce of effort, or a morsel of protein-rich snack.
A little P.S.–Would it surprise you to know that science-fiction writers have consulted with Hanelt when they’re stuck on some point of plot development, and need some inspiration?
all about nematomorphs
(Ben Hanelt photo by University of Nebraska-Lincoln; dead host cricket and a hairworm in a New Mexico stream by Ben Hanelt.)