Flies are supremely successful animals, but they tend to get a lot of bad press and let’s be honest, the way they look and what they get up to doesn’t do them any favours. For me, the most unnerving yet fascinating flies are the keds (also known as louse flies and hippoboscids). Whatever you want to call them, there’s no getting away from the fact they look a bit nightmarish.
Just take a look at the photo below. This species, Crataerina hirundinis, takes liberties with house martins. The specimen in question was found on a young house martin that had fallen from its nest. Not only do they have something of the night about them, but these flies which have forsaken flight, scuttle about in a manner and at a speed, which makes you squeal like a girl. If you’re ever in the unfortunate position of having one of these on your person you’ll see what I mean. One moment it’ll be on your hand and the next it will have scampered, quite crab-like, to your armpit to seek refuge amongst the warm tangle of hair. One of these varmints in the trousers is not worth thinking about, but I’m sure some enterprising soul back in the middle ages probably devised some sort of torture device consisting of a handful of louse flies and a pair of metal trousers.
Repugnant appearance aside they’re actually beautifully honed to a parasitic way of life. The body is flattened and the wings have all but disappeared so they can crawl about with ease in the bird’s pelage. The feet are like grappling hooks, giving the insect a tenacious grip. With all these adaptations they scuttle around the body of the host with impunity searching for a good place to suck blood from after piercing the skin with the stylet-like mouthparts.
What I find most disturbing about these flies is their size in relation to the host. I suppose it would be something like a human playing host to a parasite the size of an edible crab.