Top Gun (Machimus cyanopus, Asilidae)

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When we talk about flies often comes to mind the archetype of the “flesh fly” i.e. something more or less big and more or less black that doesn’t fly very skilfully while doing “bzzzz”, and which likes to wallow in the faeces. It’s hard to imagine that among these flies there are real aces, whose agility and fight tactics would make Top Gun pilots look like amateurs. These badass flies are the Asilidae, commonly called “robber flies” or even “assassin flies”!

Asilidae are, as the suffix -idae indicates, a family, belonging to the order Diptera. Like all the Diptera (with a few exceptions), they only have two wings and are holometabolan: from the egg comes out a larva that will end up transforming into a pupa, and from the pupa will emerge the adult. A first difference between them and the “usual flies” is their diet: Asilidae are carnivorous at adult stage. And everything is good to eat: other flies, bees, wasps, beetles, dragonflies… These desperados are not afraid to tackle bugs that have the means to retaliate. To gain some advantages over these prey which for some of them usually occupy the hunter role, Asilidae have developed excellent flight control and have very good agility and view. They even use bold hunting techniques! These aren’t really stray bugs, flying erratically looking for prey. They are more relentless. They ambush at the top of a fortune promontory, and then wait to spot an insect they could hunt with their excellent vision. Once a prey is spotted, the attack begins; often the prey is intercepted in flight!

Their morphology reflects this particular way of life. Asilidae have large and strong spines on their legs, notably on their 1st pair of legs, allowing them to firmly hold their prey. And when you intercept an insect in flight, it’s better to well grab it. On their face, we can see many bristles called mystax (or moustache). This barrier serves them to protect their eyes from possible defensive movements of prey. Asilidae have a specially modified proboscis to be able to break through the cuticle of the insects they catch, preferably at their weak spots. To neutralize their prey, Asilidae inject a cocktail of neurotoxic materials and enzymes to liquefy the inside. Asilidae will suck the resulting soup.

Identifying an Asilidae is not easy in most cases. This is a very diverse family, and you often need to have access to specific criteria to determine the species and to use the existing keys for this family. Here the ovipositor at the end of his abdomen (the black part) indicates that one is a female, the habitus, the study of the different bristles of his body as well as the shape of the ovipositor indicates that it is a female Machimus cyanopus.



Last update: February 22, 2021

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