The natural world is full of examples where one organism has evolved to look remarkably like another, a phenomenon known as mimicry. A black and yellow insect buzzing near a flower often suggests a bee or a wasp. However, many flies have evolved color patterns, body shapes, and behaviors that closely resemble these stinging insects. This visual deception is an effective survival strategy, allowing the harmless flies to gain protection from predators. Understanding these differences can help you distinguish the harmless imitator from the true stinger in your garden.
The Master Mimics
The most common and successful bee imitators belong to the family Syrphidae, commonly known as hover flies or flower flies. These flies often feature the bright yellow and black stripes characteristic of wasps and yellow jackets, making them highly convincing. Species like the drone fly closely resemble the domestic honeybee, including a similar fuzzy appearance.
Another prominent family of mimics is Bombyliidae, or bee flies, which are plump and densely covered in hair, making them look like small, fuzzy bumblebees. Many bee flies hover near a flower while using a long, slender proboscis to sip nectar. Certain species of Robber Flies (Asilidae) also participate in this masquerade, with some being excellent mimics of bumblebees.
The disguise is customized to imitate different types of bees and wasps across various ecological niches. Robber fly mimics, for example, have a predatory lifestyle, ambushing other insects, including the very bees they resemble.
Key Differences for Identification
The most fundamental difference between a fly mimic and a true bee or wasp lies in the number of wings they possess. Flies belong to the order Diptera, meaning “two wings,” having only a single pair of functional wings. Conversely, all true bees and wasps are part of the order Hymenoptera, meaning they have two pairs of wings, totaling four.
Antennae and Eyes
Observing the insect’s head provides a clear distinction, particularly by examining the antennae. Flies that mimic bees usually have very short, stubby antennae. Bees and wasps possess longer, more obvious, and often segmented or “elbowed” antennae.
The eyes offer another reliable clue. Many fly mimics have disproportionately large eyes that cover most of the head and frequently meet or nearly meet at the top. In contrast, a bee or wasp will have smaller, more widely separated eyes positioned on the side of the head.
Body Shape and Behavior
The body shape is also telling. Flies often have a stout, less segmented body, while most bees and wasps possess a distinct narrowing, commonly referred to as a “wasp waist,” between the thorax and the abdomen.
Behavioral cues can also help differentiate the insects in the field. Hover flies earned their name because of their characteristic ability to hover almost perfectly still or dart erratically. Bees tend to fly in a more direct path between flowers, moving less suddenly and rarely remaining suspended in a stationary position.
The Science Behind the Disguise
The evolutionary phenomenon driving this remarkable visual deception is known as Batesian mimicry, a concept named after the 19th-century naturalist Henry Walter Bates. Batesian mimicry occurs when a harmless species, the mimic, evolves to imitate the warning signals of a species that is genuinely dangerous or unpalatable, the model. In this case, the non-stinging flies are capitalizing on the defensive reputation of the stinging bees and wasps.
The model species, such as a bee with its venomous sting, possesses aposematic coloration—the bright yellow and black patterns that serve as a danger signal to potential predators. Predators, such as birds or reptiles, learn through negative experience to associate these colors and shapes with a painful outcome. Once this association is established, the predator avoids any insect bearing the warning pattern, whether it is the true stinger or the harmless fly mimic.
This strategy provides the fly with a significant survival advantage without the metabolic cost of producing venom or developing a defensive apparatus. By simply wearing a costume, the fly gains an immediate layer of protection from predation. The success of the mimicry relies entirely on the presence of the genuinely dangerous model to maintain the predator’s learned aversion to the shared warning signs.