Many birds feast on insects. Some of these insects can fight back, some cannot. If you are one of those tasty, but defenceless insects, what better tactic could you develop than to make the bird think you were actually a well armed something else?
This tactic is called Batesian mimicry: a defenceless species evolves to imitate the warning signals of a well armed one. Batesian mimicry is easy to see among flies who frequently do a remarkably good job of mimicking the better armed bees (and wasps).
Here is an example just seen in my garden: a bee and its lookalike fly. Now, I don’t actually know the species of either of these. (Possibly the bee is a Bombus bifarius queen, and the fly is a Criorhina sp.) Whatever the species, the fly is mimicking the bee, and doing a rather good job of it.
This is the bumble bee (note its long antenna). This insect can sting.
This is the lookalike fly (note its stubby antennae). If you were a bird flying by, would you be able to tell that this one was safe to eat?
