It’s a spider, it’s a crab…. no it’s a fly!
Many cavers and bat workers have observed small but conspicuous, shiny, black domes on the roofs of caves occupied by bats (Fig 1). When curiosity drove me to put one of these domes under a microscope, it was clear that these tiny structures are some organisms: the pupae (or immature stage) of insects.
Figure 1: Pupae observed on a cave roof; this specific specimen is slightly damaged. (Photo: Werner Marais).
The adults are the ugliest bugs I’ve ever seen (they might even give Steven Spielberg a fright….). They are spider-like blood-sucking parasites, known as bat flies or bat louse flies from the insect order Diptera, which means they are actually true flies. This unique family of flies, the Nycteribidae, is highly adapted to feeding exclusively on the blood of bats; no case has been recorded where they were feeding on any animal other than bats. The eyes are reduced or absent, the head is very small and bent backwards, and the legs are robust and armed with strong claws for clinging on to the bat (Fig 2). They are wingless and totally incapable of flying, being distributed by the bat flying to different caves. It’s easy to mistake them for spiders, but note that they have only six legs where spiders have eight.
Figure 2: A wingless bat fly viewed under a stereo microscope; its small head is at the top of its body in this image. (Photo: Werner Marais).
When the shiny round pupa is ready to hatch, the warmth and physical closeness of a bat will encourage the young insect to break out of the pupa.
Their body length is 2-5mm (Fig 3); now imagine the size of such an intimidating parasite in relation to a cave bat… that’s almost like a dinner -plate-sized, blood-sucking bug in relation to a human being!
Figure 3: A bat fly parasite on the head of a Schreiber’s Long-fingered bat. Note the large size of the parasite in relation to the bat (Photo: Werner Marais).
Holy flying fox! It's a nursery for orphaned bats
