Microdon

Image: N Sloth

It sounds like a dinosaur but it looks like a... slug?

I know, I know. It sounds like my last marble has finally slipped out of my grasp, hit the ground with a thunderous clink and is even now rolling away with a peculiar air of regret. But hear me out.

Image: Adam Furlepa

Sure, adult Microdon are clearly flies. Hoverflies, to be precise. Big ones, at up to 1.5 cm long, and stocky and hairy enough to threaten people with a bee sting they don't actually have. Mimicry of bees and wasps is quite the tradition among hoverflies, and Microdon upholds it with aplomb. There are some 250 species, and they can be found all over the world.

So much for the adults. Larval Microdon?

Image: Malcolm Storey

Now they're different. Very different. They don't even look like maggots! If they looked like maggots that would just be normal different, but these guys are different different.

The first time larval Microdon were found people thought they were some sort of mollusc, a strange slug-type-thing. Later they thought they might be scale insects.

Image: Malcolm Storey

You can see why, with their near total lack of body parts and a sticky underside that looks a lot like a slug's foot. To make matters worse, these sluggish creatures live in ant nests! This is quite the feat for something that isn't an ant. Normally ant nests contain only ants and food, often dismembered food. But Microdon has a few tricks up its, er, up its... It has a few tricks.

Adult Microdon lay their eggs at the mouth of an ant nest. And then they fly off. Quickly. If you're not an ant, and precisely the right kind of ant, you DO NOT want to be found at the mouth of an ant nest. Unless of course you're so desperate to get in you don't mind doing so one body part at a time.

Image: tom murray

Oddly enough, that's almost exactly what larval Microdon do. They hatch out of their eggs and immediately crawl into the nest. They produce chemicals that smell like ant pheromones, so the ants don't recognise them as intruders. And the flat shape means the larvae can press themselves against the walls and try not to get in the way. They can even roll up and pretend to be an ant cocoon. It's so convincing that ants will happily pick them up and carry them to the safety of their nurseries.

And how does a larval Microdon repay all this hospitality? It eats their young of course! It's like that lodger who always finishes the last bit of orange juice, only worse because, you know, it's babies. Really tiny larvae have been seen cutting holes in ant cocoons and crawling inside, where they feed on the contents. When they're too big to do that, they simply crawl around in the brood chamber, feasting on defenceless young. It's quite the banquet if pesky morals don't get in the way.

Image: Algidus

After all that abundance of protein-rich food, the larval Microdon crawls up to the entrance of the nest and pupates. It still releases those pheromones, so the ants treat it like a well-regarded bit of nest architecture. Then, when the ants are deep within the nest sleeping, an adult Microdon finally emerges. It doesn't have those ant pheromones any more so it scrambles out of the nest and flies away as quickly as possible. They DO NOT want to be found loitering in an ant's nest!

But what's up with that dinosaur name? Microdon means 'small tooth', and they're named that because a lot of the adults have little spikes on the corners of one of their thoracic segments. Clearly, this is a name they acquired before anyone knew of their dark and murderous past, deep in the nests of ants.