Do insects grieve?

 We tend to think of grief as human. Maybe, we'll acknowledge, dogs can grieve. Horses can absolutely grieve, I've seen it.

So, higher social mammals?

Birds? Crows show behavior that looks very much like grief.

Insects? Surely not.

Fruit flies?

A study shows that a fruit fly that finds/sees a dead fruit fly...may get depressed. Fruit flies that witness a large number of dead fruit flies can actually live 30% less than ones that didn't.

Does this mean fruit flies grieve?

It's likely that an aversion to large numbers of dead bodies is, in fact, a survival mechanism. So it's possible that grief started as a way to avoid being infected by stuff and led to more complex behaviors...human funeral customs serve, in part, the purpose of properly disposing of corpses so they don't attract disease.

But fruit fly grief being a thing is quite...fascinating.