Damn, Nature, You Scary: Phorid Flies

Flies are, most people would agree, pretty disgusting. They drink their own spit. They feed on dung, they feed on rotting animals. Some fly species don’t even wait until the animal is dead, preferring to suck blood from living mammals, vampire-style, to secure the protein they need for their eggs. Others are even more vicious – when peckish, they grab hold of fellow insects, stab them quickly with their proboscis, and suck out all of the unfortunate victim’s organs. As an order, flies have very few qualms about what they do to get their food.

The phorid fly, however, is a standout example of nastiness even among this compound-eyed rogues’ gallery. This particular family of flies is extremely diverse – some of their larvae scavenge, some are predatory, some are parasites, some are even vegetarian. However, the relatively PG first and last type rapidly pale into insignificance when we take a look at their less ethical counterparts. A quick scan of the names of some phorid flies throws up some worrying examples – the coffin fly, the bee-killing fly, the zombie fly, and, last but not least, the superbly self-explanatory ant-decapitating fly.

Maybe I shoulda gone with ‘Dave’ after all

It doesn’t stop there. As it turns out, there’s more than one way to decapitate an ant; recently researchers found that adult females of a particular phorid fly genus (Dorniphora) frequently feed on passing ants by decapitating them and, as per usual, draining their internal organs. At least it’s a quick death, right? Phorid fly swoops down from the sky, slice goes the head, you’re off to the great anthill in the sky before your tiny invertebrate brain has the chance to realise anything’s wrong.

Nope. Sorry.

First, the fly has to select its victim. Here’s a quick size comparison:

Dohrn longi plate

I’m not liking these odds

Clearly, taking on a healthy ant is not a realistic option. Instead, it has to wait until an injured ant stumbles across its path. But the fly still needs to be wary; even a weakened ant could be dangerous. It needs to establish for certain whether the ant is weak enough to feed on. How does it do that? By flying in circles round a potential victim, poking it, and pulling its legs and antennae, duh. Think kindergarten bully, but with wings.

What an asshole

Once it’s decided the ant is lunch potential (if not, the fly will simply buzz away to find a better victim), the fly settles on the ant and begins to probe it with its mouth. One species has a modified proboscis that functions like a crude knife, helping it to cut through the nerves, membrane and gut of the ant. Others just have to puncture the ant’s carapace with the usual blunt mouthparts. ‘Eventually’ (the process was not designed with ant comfort in mind), the fly will manage to loosen the head, and then yank it off. The study found that a minimum of about eight minutes were needed to achieve decapitation – usually, though, it took longer, as the fly needed to break to fight off passing insects. Ouch.

ant nom

This is an ant getting its revenge on a phorid fly. It may make you feel better. I’m not sure

That’s ant life: you’re born, you’re probed, a fly pulls your head off with excruciating slowness and devours the contents. C’est la vie.

(It’s also worth noting that the flies ‘usually’ arrived flying in copula, as the paper put it. Ah yes, the classic post-coital ant decapitation. They said romance was dead.)

One question remains – why? Not only is it disgusting and, presumably, not very enjoyable for the ant, but removing the victim’s head and then dragging it into the long grass to snack on at leisure requires a lot more effort than, say, settling down to a nice steaming heap of dung. Dissections of would-be decapitators at the scene revealed that their ovaries were empty, suggesting that the whole gruesome process probably serves to give them the nutrients they need to form and mature eggs. Mother-love at its finest.

A similar motive is responsible for the other type of ant decapitation on the market, carried out by what are commonly known as ‘humpbacked’ phorid flies (Pseudacteon). These flies, at least, are quick; the female descends on a fire ant, their prey of choice, inject a single egg, and speed away.

Ovipositor of a Pseudacteon fly, used to insert eggs into their victims. Not nice   

Their larvae, unfortunately, aren’t quite so quick. The egg hatches, and the larva migrates slowly through the body of the ant until it reaches its head, which can take from two to three weeks. It then forms a pupa, consuming the contents of the ant’s head to keep its strength up as it does so. As a rule, having your brain sucked out is fatal, and the fire ant is no exception. The head, growing pupa now concealed snugly inside, falls off, and after two or three more weeks an adult fly will struggle its way out through the decapitated ant’s mouth. If its egg was planted in a sufficiently large ant, the fly will likely be a female, and will grow up to insert its ovipositor into fire ants of its own, just like mama.

Happy birthday to you, happy birthday to you, happy birthday evil death fly, happy birthday to youuu…

And, just in case you needed any more reasons to hate the phorid fly, some researchers have suggested that they may be responsible for colony collapse disorder. Colony collapse disorder (CCD), the bizarre syndrome currently without a widely agreed explanation in which worker bees suddenly abandon their hives, has already led to serious financial losses and fears about food crises to come, as many crops lose their most loyal pollinators. The phorid flies may act as carriers of diseases that have been linked to CCD, spreading the infection as they lay their eggs in unsuspecting honeybees.

In summary: phorid flies are homicidal, gross, downright mean, and could maybe even cause mass starvation. Thanks, nature.

Sources:

  1. Brown, B.V., Kung, G.-A., Porras, W., 2015. A new type of ant-decapitation in the Phoridae, Biodiversity Data Journal.
  2. Casuso, N.A., Mortensen, A.N., and Ellis, J.D., 2014. Zombie Fly (suggested common name) Apocephalus borealis Brues (Insecta: Diptera: Phoridae), University of Florida
  3. Morrison, L.W.. Pseudacteon spp. (Diptera: Phoridae), Biological Control Site (Cornell University College of Agriculture and Life Sciences)
  4. Core, A., et al, 2012. A New Threat to Honey Bees, the Parasitic Phorid Fly Apocephalus borealis, PLOS ONE.

Image sources: 1, 3, this and this. Header image from here.

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