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.
Reference ($$$)
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That is good mimicry! The eyes and wings would have convinced me that the fly was a fly & not a wasp but the bobbing abdomen would have given me enough doubt that I wouldn’t have poked it!
“One question is why it’s the larger flies that engage in behavioural mimicry.”
It’s probably related to the scale of the predators and the methods they use for finding prey. This will only work for large predators that hunt by sight. It’s no defense at all against small predators that hunt my smell, or probably even for small ones that use sight. The predator has to be big enough to get the right perspective to be fooled.
Another example of the extra things that flies do to mimic wasps (hey, I gotta use my education for something):
This one has its antennae on the end of a long stalk on the head to mimic the long antennae of wasps. The same one has two-toned wings to mimic the overlapping and folded wings of specific wasps.
Is it a matter of the mimic flies being similar in size to the wasps they are mimicking?
I suppose they need to be the size of wasps or bees that can hurt when they sting. There are small wasps, but any stinger they have would be ineffective against a predator. There is no fitness value in little insects mimicking ’em.
A behaviour and colouration. And two nations separated by a common language.
“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.”
Matthew, some flies that mimic wasps fold their wings longways like wasps. One such species frequently gets into my house (in Ecuador). It is an unnerving mimic. Even though I know it is just a fly, it still scares me every time I am surprised by one.
To my eye, this fly does have typically short fly antennae, but what it is doing is using its first pair of LEGS to mimic the long antennae of a wasp(the actual antennae are mounted in the centre of the head). The legs are also black, unlike the other pairs of legs. You can see in the video it even moves those legs around in a wasp-like manner, appearing to palpate the surface of the leaf.
Using its legs to mimic antennae may have been quicker and easier to evolve, as they were already the right sort of length to do the job. Ain’t evolution good at cobbling solutions together like that!
An absolutely wonderful piece of morphological and behavioural mimicry!
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