Q: Why do those little flies conspire to ruin my beer by committing suicide in it?
J.S., Moonee Ponds, Vic

They’re attracted to the aroma of beer, just as you are. Their problem is, they don’t have your capacity for it, hence they don’t last long once they make the mistake of falling in. Alcohol is a poison, as you know.

The little flies are drosophila, also known as fruit flies or vinegar flies, and they’re often seen on rotting or overripe fruit or vegetation. They love to lay their eggs in this, which is why they hang around your fruit bowl. Their concealed weapon is acetic acid, the acid of vinegar, which they carry around with them. They are only tiny – about the size of a small ant – but they can do terminal damage to an open bottle of wine or beer, or a glass left unattended.

In wineries, they’re the number one pest during vintage. Winemakers must scrupulously cover any vessel containing wine or fermenting juice, as these critters are magnetically drawn to it. If allowed to land en masse on the surface of red wine, which is often fermented in an open-topped vat and therefore vulnerable to fly attack, they can ruin the lot.