By some strange twist of fate, Bug of the Week finds itself in jolly old England at Marks Hall Gardens. In this spectacular landscape, bumble bees cloaked in white, orange, and yellow fur hastily gather nectar and pollen from dazzling wildflowers and beautiful beds of annuals and perennials. Great Britain has a rich fauna of bumble bees tasked with keeping the flowering plant world healthy and fruitful.
Like many species of social bees, bumble bees pack a potent stinger armed with venom designed to bring memorable pain to nosy predators. A clan of clever flies called syrphid flies, a.k.a. flower flies or hover flies, freely forage on nectar and pollen side by side with the bees. Flower flies lack stingers and are more or less defenseless save for one remarkable trick. Many species of syrphid flies, particularly those in the genus Volucella, bear a striking resemblance to the bumble bees with which they share the bounty of blossoms. What mystery underlies the remarkable similitude between a bumble bee and these pollinators? The answer to this question was first formulated by the 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 these distasteful compounds and where thereby rejected as food by potential predators. Bates observed other species of butterflies which had consumed nonpoisonous plants as larvae that 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 rarer tasty species that mimic the models to gain protection from predators.
While a white-tailed bumble bee forages on nectar, a syrphid fly mimic rests on foliage nearby, protected from predators by its close resemblance its stinging six legged relative.
What has this to do with our bumble bees and syrphid flies? Birds and other predators with keen vision and adroit brains learn at a young age not to mess with insects bearing stingers lest they receive a nasty surprise. By closely resembling a bumble bee, Volucella escapes being a meal for an experienced predator that has learned a lesson from a well-defended bee. How can one distinguish artful syrphid flies from bees? One easy way is to count the number of wings. Bees will have four (two pair) and flies will have two (one pair). If you are bold and willing to get close enough, you will also see that syrphid flies have rather short antennae often adorned with feathery plumes or a stout hair. Their bumble bee models have much longer antennae with a long segment nearer the head that creates a bit of an elbow with shorter segments further away. On your next trip to the garden keep your eyes peeled for bees and also these artful masters of mimicry.