A fly would be wonderful, but that's partially the insectophile part of me speaking.
Oooh, maybe you should look into insect mimics like dead leaf insects, or even just ones that mimic other insects.
The
progressive bee fly and the bee fly in general doesn't seem to be a true mimic (as in actively mimicking other insects or organisms for camouflage or defense), but it has behaviors very similar to that of the bumblebee. There's some info on them
here.
More obvious examples of mimics include walkingsticks and walkingleaves, though I believe there are also some species of beetle that have dead leaf patterns. There's also butterflies and moths with wings that resemble leaves.
If you like the idea of mimics but don't want an insect, I suggest the cuckoo. The female lays the eggs in the nest of another bird, and hilarity ensues as the baby rapidly grows larger than the surrogate mother! XD Not exactly a true mimic, but still pretty cool.