Where the abdomen joins the thorax, symmetrical medial dark patterns with marginal patches of pale yellow give this hover fly a convincing wasp-waist look. Notice how the longitudinal stripes on the thorax of the fly resemble the light colored stripes on the back of the paper wasp pictured below.
Paper wasps are frequent visitors to goldenrods. Is this wasp the model for the Helophilus syrphid fly?
As we have seen in recent episodes, late blooming members of the aster family are magnets for nectar seeking pollinators like bees and beetles, and for the stealthy predators that dine on them, including ambush bugs and assassin bugs. On a recent adventure to Chincoteague Island, I encountered an amazing dawdling goldenrod loaded with hungry aerialists gathering nectar in the warmth of the coastal sun. At first glance, the buzzing horde appeared to be a mass of bees and wasps, but on closer inspection most of these fliers bore one pair of wings, not two. Bees, wasps, and other winged members of the Hymenoptera clan have two pairs of wings. By contrast, members of the fly clan have but one pair, not two.
Late blooming members of the aster family including goldenrods are magnets for nectar seeking pollinators like syrphid flies, bees, and wasps.
So what’s the deal with flies that mimic bees? We explored this question last year in the episode “A bee or not a bee” where we learned the clever truth of the Volucella syrphid fly that mimics the white-tailed bumble bee to gain protection from predators. This form of mimicry is called Batesian mimicry in honor of renowned British naturalist Henry Walter Bates. During his travels to the Amazon, Bates noticed the striking similarity in color patterns of many different species of butterflies. Some of these butterflies consumed noxious plants as caterpillars, sequestered distasteful compounds found in these plants, and were thereby rejected as food by potential predators. Bates observed other species of butterflies that had consumed nonpoisonous plants as larvae, which bore a striking resemblance to the noxious butterflies. By resembling distasteful species, known as models, these mimics gained protection from visually hunting predators. The term Batesian mimicry describes the relationship between common distasteful models and tasty species that mimic the models to gain protection from predators.
Unlike some larvae of flower flies that are fierce predators, the larvae of Helophilus live in aquatic or semiaquatic habitats and are called rat-tailed maggots by virtue of a long breathing tube on their rear end.
In the case of the swarms of syrphid flies, a.k.a. hover, drone, or flower flies, many of these harmless and beautiful species mimic fierce stinging insects including bees, wasps, and hornets. Some believe that in addition to mimicking their stinging models in form and color, the audible buzzing of these flies may mimic the sounds of their fierce stinging models. However, a clever study comparing the acoustic signatures of models and mimics under simulated predator attack found little support for this notion. In the waning days of autumn, take time to visit the meadow or your flower garden and search for these masters of disguise.
References
Bug of the Week thanks Dr. Shrewsbury for providing an image and inspiration for this episode. The interesting article “Do hoverflies (Diptera: Syrphidae) sound like the Hymenoptera they morphologically resemble? “ by A. Rashed M.I. Khan, J.W. Dawson, J.E. Yack, and T.N. Sherratt was used in preparation of this story.