by Matthew Cobb
This video, posted by Chris Hassall, shows a hoverfly – NOT a wasp – sitting on a leaf.
You can tell it’s a fly because it’s only got one pair of wings (it’s a DI-pteran), and those wings aren’t folded longways when at rest. Plus both the eyes and the antennae are fly-like, not wasp-like (I guess those antennae also gave rise to its species name – Spilomyia longicornis [‘long horns’]). Those colours and morphology would be enough to ward me off if I were a predator. It sure looks like a wasp.
What’s intriguing is that this species has gone a step further – it not only looks like a wasp, it behaves like a wasp. Look at the way it moves its legs and wings. That’s not what flies normally do – it looks very wasp-like indeed.
In the information under the video, Chris writes:
Behavioural mimicry occurs when an animal acts like another animal in order to deceive a third animal. In this video (taken by Dr Henri Goulet), you can see the fly wagging its wings in a manner characteristic of wasps, repeatedly tapping its abdomen against the flower (although flies cannot sting), and holding its dark forelegs in front of its head to mimic the longer antennae of wasps.
Research conducted at Carleton University, Agriculture and Agri-Food Canada and the University of Leeds has shown that only those hover flies that look most like wasps exhibit these kinds of behaviours.
Here’s the abstract of that research; the full paper will shortly be published in The American Naturalist:
Palatable (Batesian) mimics of unprofitable models could use behavioral mimicry to compensate for the ease with which they can be visually discriminated or to augment an already close morphological resemblance. We evaluated these contrasting predictions by assaying the behavior of 57 field-caught species of mimetic hover flies (Diptera: Syrphidae) and quantifying their morphological similarity to a range of potential hymenopteran models. A purpose-built phylogeny for the hover flies was used to control for potential lack of independence due to shared evolutionary history. Those hover fly species that engage in behavioral mimicry (mock stinging, leg waving, wing wagging) were all large wasp mimics within the genera Spilomyia and Temnostoma. While the behavioral mimics assayed were good morphological mimics, not all good mimics were behavioral mimics. Therefore, while the behaviors may have evolved to augment good morphological mimicry, they do not advantage all good mimics.
One question is why it’s the larger flies that engage in behavioural mimicry. Maybe predators are smarter than we think, and can see in the larger flies that the wings and eyes and antennae indicate this could be a tasty morsel, so those flies have ended up going the extra mile and evolved behaviours that would convince even the most dubious predators that this is NOT a fly (which of course it is), but instead a wasp.
Heather D. Penney, Christopher Hassall, Jeffrey H. Skevington, Brent Lamborn and Thomas N. Sherratt (in press) The Relationship between Morphological and Behavioral Mimicry in Hover Flies (Diptera: Syrphidae). The American Naturalist.