It's not limited to insects but includes other arthropods (example: post #4524130 and post #5115241). I think it is most common with arthropods with a rather identifiable abdomen. bee girls and ant girls are probably the most common type to be depicted with them though.
There are some examples though where other parts of the body besides the abdomen is used as a tail, though will note these all appear to be arthropods that lack an abdomen in their anatomy: post #6094877, post #6606171, post #5113470
