Sunday Spinelessness - Flightless flies

You might be wondering how you can given the name "fly" to a flightless creature. Taxonomic groups reflect the evolutionary history of life. So for instance the great ape family contains orangutans, gorillas, humans and chimps because all these species descend from a shared common ancestor. When entomologists talk about "flies" they are referring to the taxonomic order Diptera - a group of insects that share a common ancestor that lived approximately 250 million years ago. Of course, organisms don't come with little tags telling us where they came from, it's the job of taxonomists to find characters that can be used to reconstruct that evolutionary history. The character that most sets flies apart from other branches of the insect tree of life is the presence of "halteres" - the stubby yellow structures  this predatory robber fly is modelling (more on that fly here).

Diptera means "two winged" and the name refers to the fact that most flies get about with one pair of wings, having reduced their second set into the flight-satablising halteres. This little innovation has allowed dipterans to become precision fliers, and one of the most successfully groups of organisms on earth with about 150 000 species (maybe 10% of all species are flies).

The true flies in order Diptera all descend from an ancestor which flew with two wings, but many of the species that descend from that ancestor have given up their wings. Because taxonomic groups are reflections of evolutionary history even wingless species are still flies - you can call them the apterous members of Diptera (wingless two-winged insects).

Flightless hippoboscids

Bat flies, Bat flies, Bat flies

Bats seem to attract flies like... well they seem attract flies. At least three different lineages of flies have evolved a close relationship with bats. The largest group are, unsurpsingly, called "bat flies" (the taxonomy of this group is uncertain, but it includes the family Nycteribiidae). I have a soft-spot for most bugs, but even I have to admit bat flies are pretty gruesome looking creatures:

The bat flies have lost their eyes as well as their wings, by have made up for those loses in other body parts. The massive spider-like legs end in tiny claws that let the flies grip on the bat's fur and move about. Once stuck on a bat these flies drink blood.

The fauna of New Zealand is very keen of flightlessness. Charasmatic mega-fauna like moa, kiwi and kakapo are the obvious examples, but we are also one of only two places on earth to have flightless perching birds (our three wrens are now extinct, as is the Canary Island Bunting). There are no truly flightless bats, but our short tailed bat is probably the closest thing - spending most of its time crawling around the forest floor. Our terrestrial bat hosts its own flightless flies. Apparenlty Mystacinobia zelandica descends from a blowfly but its association with the short talied bat has changed its body so greatly that is was not originally considered to be a fly at all, and thought to represent a unique order of insects. I couldn't find any photos of Mystacinobia avaliable with a permissive license, but check out the New Zealand Geographic story and Te Ara's article, which even has a video.

Mystacinobia has been placed in a family that is endemic to New Zealand, but there is one fly family with an even more restricted range. As far as we know, the family Mormotomyiidae is represented by a single species (Mormotomyia hirsuta) which is only known from a particular site in on one mountain in Kenya. As you may have guessed the site is a bat roost, and the animal, despite being only distantly related to the other bat flies discussed above, has taken on the spidery form that is associated with flies that spend their lives with bats.


Mormotomyia doesn't have the hooks that other species use to cling on to bats, so it may be a little more free-living than than the species discussed above.

Phorids

The family Phoridae might be the strangest group of flies . Hell, one genus is made up entirely of flies that burrow into the heads of ants, decapitate them, and use the severed head as a cocoon.

I'm going to end this brief survey of here, but I want to emphasise that these are just a few of the flies that go against their name. I could have talked about "snow fleas", or "bee lice",  in fact the flylogeny project records about 40 families with at least some flightless members. When the Daily Mail ran a story on the rediscovery of the Kenyan bat fly Mormotomyia hirsuta one of that newspaper giant page-view creating algorithm's readers felt they needed to add this opinion to the ensuing discussion:

That looks nothing like a fly. How come this evolved into a 'walk' ? It makes no sense. If I could fly I wouldn't evolve into something flightless. Evolution is flawed

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