Hover flies (Syrphids) cannot sting or bite but instead have evolved the narrow waisted body shape and/or coloration like stinging bees or wasps and some even sound like them with the humm their wings make when flying. The more the fly species look like a species of dangerous insect the less they suffer from predators that cannot tolerate the sting, so they avoid that prey type. The fly shelters under the avoidance behaviors of predators towards stinging insects that share a Mullerian warning coloration and body plan.
A rare harmless flatworm (Pseudoceros imitatus) copies a toxic sea slug (Phillidiella pustulosa) so it can share in the antifeedant protectio of a warning pattern. http://rfbolland.com/okislugs//phylpus2.html