To the casual obeserver the following insects look like bumblebees. In fact they are hoverflies mimicking bumblebees – very clever impersonators!
Obviously bumblebees have a sting which they use as a deterrent – a young bird which catches a bumblebee will inevitiably get a nasty painful sting. That sting will kill the bumblebee but will act as a deterrent the next time that bird sees a bumblebee. Instead of catching another bumblebee it will go and hunt something else.
By mimicking bumblebees the hoverfly will gain the ‘group’ protection of looking like a bumblebee!
Funny thing evolution!