Wild Side: Deer keds

Still another blood sucker.

A deer ked, viewed through a microscope at a magnification of about 20 times. — Matt Pelikan

The conservation organization I work for (The Nature Conservancy, nature.org) shares office space with a smaller, newer, and locally fledged nonprofit, BiodiversityWorks (biodiversityworksmv.org). B-works, as I call it, conducts a range of wildlife studies, monitoring projects, and management; these efforts take the energetic B-works staff into the field all across the Island.

One result is that strange stuff keeps turning up in our office: for instance, plant specimens seeking an ID, snakes awaiting radio transmitter implants, and dead stuff, lots of dead stuff (most recently a Cooper’s Hawk, done in by a cat the bird imprudently attacked).

So it is not a surprise to hear one of the B-works staffers calling, “Hey Matt, I’ve got a strange bug for you!” But recently, B-works wildlife biologist Liz Baldwin brought in a real corker.

It had evidently latched onto Liz in the field and then, she thought, bitten her. Squat, brown, and just a few millimeters in length, the mystery critter suggested a tick at first; it was clearly designed to cling to a larger species and, presumably, feed off of it. But a quick leg count turned up only six, two shy of a tick’s complement and the right number for an insect.

I dispatched the little devil in a killing jar and popped it under the bright LEDs of the Conservancy’s dissecting microscope. Magnified 20-times or so, this was an insect that even I found shocking. Plump-bodied with robust legs, it was covered with stout hairs, lying flat on the body and facing toward the stern. Large eyes dominated the front of the head but didn’t hide a long, thin proboscis — suitable for puncturing hides. Each of those six legs was tipped with a couple of strong, curved claws, clearly designed to grab onto hair and hang on tight.

Most significantly, though, I noticed the stubs of two broken-off wings, accompanied by a pair of tiny, pale, lollypop-like structures. Halteres, they’re called, basically the evolutionary remnants of a second pair of wings that flies don’t have. One pair of wings plus halteres? Improbable as it sounded, this thing was a fly!

The ID process was easy from here. Though I’d never seen one before, I realized it must surely be a louse-fly, in the family Hippoboscidae. With few members of the family occurring in our region, I quickly zeroed in on something called the deer ked, Lipotena cervi.

I had never heard of these, but a little web searching turned up a truly bizarre life history. Adult keds, with a full pair of wings, fly about until they spot a likely host (preferably deer or moose, but sometimes other warm-blooded species). They’re instinctively drawn to large, moving objects. Burrowing into the victim’s hair, the ked breaks off its wings and puts that nasty proboscis to work sucking blood.

If male and female keds end up on the same host, they mate. Inside the female, a single egg will develop and hatch, and then the larva will develop fully within the female. Rather than laying an egg, the female effectively gives birth to a larva. Apparently without feeding, the larva drops off and pupates, emerging late the following summer as a winged adult to repeat the process.

The bite is said to be nearly painless, despite the size of the proboscis, but a nasty itch often sets in a couple of days after the bite, persisting for days or even weeks. Unlike ticks, which must remain attached to host for a long time in order to fill up, keds complete their meal in well under an hour.

The deer ked is an introduced species; one source puts its arrival in North America around 1907, when it probably arrived on a shipment of live animals from its home range in Eurasia. So far, it has colonized much of the Northeast. Its distribution appears to be rather patchy, but it seems likely that this highly evolved but frankly rather repelling insect is here to stay.

When I asked around, several of my colleagues reporting running into these unusual flies. And I imagine keds are familiar to deer hunters, at least to successful ones who handle dead deer. Keds reportedly concentrate on the bellies of deer, and can be told from ticks partly because they scurry rather than creep.

So while I was caught off guard by this odd insect, they may be fairly common, and commonly encountered, on the Island. Happily, they are not known to carry diseases, either of deer or humans. And their habit of staying on (and biting) only one individual host makes them poor vectors for transmitting disease of any kind.

I’m grateful to Liz Baldwin for being a good sport about blood-sucking parasites. The episode was a fun one, reminding me of what I love about studying nature: the surprises never end.