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Xuankun Li

Assassin fly babies have ‘Swiss army knife’ mouths

Australia’s splendid assassin fly (Blepharotes splendidissimus) earns its fearsome moniker. About the size of a bottle cap and sporting a similar metallic luster, they ambush butterflies and dragonflies in midair, killing them with a venomous bite. Now, scientists have discovered that even the larvae of these flies are vicious.

The mouths of these maggots are “the insect equivalent of a Swiss army knife,” researchers report in Austral Entomology. Using scanning electron microscopy to produce photos like the one above, the team discovered blade-shaped mandible hooks with backward-pointing teeth—all the better to pierce into soft-bodied bugs in the soil where these larvae live. These hooks also have grooves that, when pushed together, form a tube the maggots use to inject venomous saliva into their prey. The venom injector tool doubles as a straw, allowing the larvae to suck out the body parts of their victims, the authors report.

The researchers also found that once the larvae pupate, usually underground or inside wood, the pupa adopts spurs and spines ultimately used by the emerging adult to drill through to the surface of soil or rotting timber so it can take to the skies.

As horrendous as they may be to bugs, the authors say assassin flies and their larvae, which have thousands of different species worldwide, can actually help farmers as they control populations of plant-feeding insect pests such as caterpillars and beetle larvae.