Bumblebee Fly and Narcissus Bulb Fly - Mallota postica & Merodon equestris
It's perhaps redundant to say given how much I've covered both insects species showcased here in the past, but they both feature very effective resemblances to the fuzzy Bees of summertime. We're a little unbalanced here with 5 pictures of a Bumblebee Fly and only 1 of the Bulb Fly (Picture 2). Regardless, these convincing disguises are such close matches that they fool most onlookers which lack sharp vision. As a result, these Hoverflies are left unbothered for fear of being stung. That's the point when it comes to Batesian Mimicry: a harmless specimen has the warning signs/colorations of a more harmful one to avoid predation. Not to burst their bubble, however, but while a solid guise, there are a various predators with sharp vision that may be discerning enough to see through the mimicry of these fluffy Flies (or just ignore it altogether). Birds in particular fit this description. To extrapolate off of one particular example from Chapter 3 of, "The Sting of the Wild", the author took note of the hunting habits of notable birds such as the Bee-eaters - birds of the Meropidae family which bash a Bee's abdomen to destroy the stinger - and more interestingly, the western kingbird (Tyrannus verticalis).
The western kingbird is a small but territorial hunter whose visual acuity is strong enough to discern male Bees from females. It accomplishes this by looking for specific features of the insects it hunts including the eyes, overall proportions, and size. Since a male Bee lacks a stinger, it is seized midflight and swallowed up as easy prey! If similar birds would be discerning enough to eventually realize that these Bee-mimics are harmless as well, they too could become easy prey. Of course, if the mimicry on display by these Flies would be ineffective, then both species would need to adapt with new defensive/evasion strategies, and typically, most predators or onlookers take strong notice of warning colorations. All that said, when it comes to mimicry of stinging Hymenopterans, there is one other factor to consider: pheromones/scents. While both the Bumblebee Fly and Bulb Fly ostensibly look the part, if either one of these species were caught entering a hive or colony, the Bee security detail would see it as an intrusion whose consequence would not be pleasant for either of the Flies.
Obtaining nectar/sweet liquids is essential for these adult Flies' diet, but if the risk to obtain nectar or honey is too great, then perhaps the use of a physical resemblance to deter predators is enough. Conversely, other Bee-mimicking insects actually have scent-related strategies which allow them to effectively infiltrate Bee colonies and obtain meals with a low risk of an attack from either a predator or an agitated colony. The prime examples of this are the Death's Head Hawk Moths (of the Acherontia genus) who not only resemble Bees superficially, but can also employ similar scents and even sounds of a colony's members in order to deter aggressive responses from the hive. That's incredible in terms of dedication and tactics! These Flies don't need to go that far, and will mainly stick to moist environments and areas with ample blooms to obtain nectar. If you spot such a Hoverfly, examine it closely. The large compound eyes are a big giveaway. It helps to know which Bumblebee or Hymenopteran mimics are flying around in your backyard, and perhaps which insects they mimic as a result too. This also goes for Bee Flies who employ their mimicry for similar reasons, and also to approach solitary Bee nests for more nefarious (but reproductively essential) purposes.
Pictures were taken on June 1st and July 1st, 2024 with a Google Pixel 4. If Stinging Insects (mentioned here) and stories about them are your cup of tea, I cannot recommend "The Sting of the Wild", by Justin O. Schmidt enough.
