Last fall, I posted about hover flies. Hover flies are pollinators of flowers with warning coloration resembling wasps and bees. It is all bluff, because hover flies cannot sting or harm predators. However, most predators have had encounters with bees and wasps that can truly sting which discourages most predators from feeding on the hover flies.
Helophilus fasciatus is a large wasp mimic. It requires close examination to note that the insect in the picture below has antennae that are typical of hover flies. (Most wasps have long segmented antennae.) Flies have 1 pair of wings. All Hymenoptera (bees and wasps) have 2 pairs of wings.
Is visual mimicry good enough to fool most predators? Or does the mimicry have additional components? A 2009 study by Rashad et al. asked the question, “Do hover flies sound like the Hymenoptera they morphologically resemble?” (Behavioral Ecology doi:10.1093/beheco/arn148). They used sophisticated audio recording and sound analysis equipment to capture sounds from hover flies and the bees and wasps they mimic. One of the species they recorded was Helophilus fasciatus. Their conclusion: they could find no evidence that the sounds were mimetic. Of course, this does not answer the question of what the flies sound like to potential predators. How well can potential predators discriminate between hover flies and bees and wasps? It may be that the the fundamental sound frequency of 174.5 Hz produced by our Heliophilus is close enough to convince most would be predators to leave them alone.
Heliophilus fasciatus is a common visitor to flowers in Summer and into Fall. They are one of the larger hover flies, about the size of a penny. Look for them in your butterfly garden.
Hover Fly, Heliophilus fasciatus
Living With Insects Blog 
Flies in disguise.
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