This is one of many apple cider vinegar traps I laid out.[/img]
Out of sheer curiosity, is it just apple cider vinegar inside that cup? Do they drown in vinegar or is there something else?
Yes, pure apple cider vinegar. Attracts around 56% of the fruit flies, above 86% if you're not around the cup.
For some reasons, fruit flies die when in contact with the apple cider vinegar, such as their wings or body. Then they stay afloat squirming until it's lifeless. And then after a while, the corpse sinks to the bottom.
Some of the flies shoot out a thin black stream of something from their stingers. I think it's poo. I don't know. The thin black lines are very long, but it dissipates shortly.
Most, if not all, fruit flies drown before their body sinks. When their heads are lower than their abdomen, after a brief moment, an air bubble pops out from their heads, and the body sinks very fast. When their abdomen are lower than their heads, their wings will catch air bubbles, and that takes a very long while for them to sink. Sometimes, I see flies just fly straight into the vinegar, so their wings hit the vinegar first. They would spin around and around until they are tired, and then poof! Out comes their stingers. Only the fruit flies with their abdomen lower than the heads do not show their stingers.
So yeah. This is what I observed while working on my project. This trap is more interesting than all of my projects.