Well my argument continues to hinge on the use of the word hole.

If the joke said rectum (or whatever the bug equivelent would be) that would be fine, because that is the excretion tube. If it just used ass, that would be fine, because that typically includes much of the rear end (as in: "Hey Herb, don't you think that ladybug's got a nice ass?"). If it used sphincter it would also be fine because it would be defining the aperture Fortunato mentions.

But an asshole is an asshole. By modifying the word ass, it is defining the part of the anus or ass that, as far as I know, is not defined by any other word. The "empty place through which one deficates." It would be similar to the mouth cavity, and the eye socket. A hole by the definitions in my dictionary does not include the walls or whatever structure surrounds the hole. Certainly the shape of the hole is determined by these factors, but the hole is the empty space. If it is not, then the phrase: "Look at the empty space in the middle of that hole." would make sense. It does not for it is a redundant statement.

And for argument's sake, I think that the specific definition of asshole adds a bit of piquancy when the term is used in a derrogatory manner. Because while the rectum and the sphincter both are wonderful - if unfortunately associated (excuse the pun) - creations of millions of years of evolution (or something that God put together in a minute or so), wereas the hole is literally nothing that is directly connected to something distasteful.

And by the way: since the rectum is a collapsible tube (at least in mammals - is there an entymologist in the house?) unless it is actively "in use", technically, we don't always have an asshole. And depending on whether the fly is aware of impending death or not, and depending on whether said fly involuntarilly clinches up due to impending death, there is the possiblity that the fly does not even have an asshole at the time of death.

But I digress...

See, to me this is funny!