Two blowflies were chowing down on a dog turd mixed with their own vomit for lunch. One of the flies burped. The other replied: "Don't be so disgusting while I'm eating!"
As anyone who has seen David Cronenberg's deeply unpleasant docu-drama The Fly can attest, flies aren't exactly the most sophisticated diners in the animal kingdom. Rather, they eat food by vomiting a mixture of saliva and stomach acids onto its surface. Ew.
This isn't to improve the flavour (we assume) but to break down food particles that would otherwise be impossible to digest.
Unlike many other types of insect, flies do not possess mandibles or other chewing mouth parts. Instead, they have to make do with a sponge-like pie hole known as a labellum. They are subsequently forced to go down the 'DIY soup' route - which is why you should always shoo these things off anything you plan to eat.
A recent science article on The Conversation explained how they pull this off:
When a fly’s feeling hungry, it will land on its food and vomit out a mix of saliva and stomach acids. These liquids have digestive proteins that help to break down the food before it even enters the fly’s mouth, turning a solid meal into a soup. Like using a straw, the fly uses its long sucking mouthpart to slurp up its liquefied meal. Their mouthparts even have sponges at the end so they fly can suck up every last drop.
Interestingly, not all fly species (of which there are over 30,000 in Australia alone) vomit on their food. Some, like the horse fly, use a proboscis to suck up nectar. As their food source is already liquid, there's no need to vomit on it. Unfortunately, their penchant for biting human ankles eradicates any points they receive for polite dining. Pesky blaggards.
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