A mimic without a model

Macroglossum stellatarum looks and behaves remarkably like a hummingbird, albeit without the “swordfighting” and high-pitched battle cries of their avian lookalikes. Selective advantage of mimicry is obvious in situations where the imitated organism is less palatable or more dangerous, or when said mimicry furthers the mimic’s own life cycle, but what if the apparent object of imitation is no longer found in the mimic’s range? Such is the case with the European hummingbird hawk-moth, which confuses birders in northern Europe in late summer. Hummingbirds are a purely New World group of birds, so what exactly are the European hummingbird moths gaining from mimicking a non-existent group of birds or, on the other hand, when is a mimic not a mimic?

If you ask your hipster friends you are sure to receive an explanation for why partaking in a trend can be a truly novel act, owing to some small esoteric twist or another. Macroglossum in the Old World may have undergone a mutual convergent co-evolution, rather than outright mimicry as the common name for these insects might suggest. Fossils of largely modern hummingbirds in Europe have been described dating to the Oligocene (about 30 million years ago). Add to that the apparent evolutionary footprint of significant pollination by hummingbirds seen in a number of Old World flowers, and it begins to look plausible that Macroglossum and other Old World humming-moths settled into a niche of pollinating long-stemmed, nectar-heavy and perch-free flowers, alongside but not dependent on hummingbirds. If your mouth-part is longer than the rest of your body combined you might as well use it, whether or not a hummingbirds are currently trending in your area. A 30 cm proboscis never goes out of style*.

This digression was kindled by a few sunny afternoons spent in the company of beautiful hawk-moths in the Tuscan hills.

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*I’m not an expert in long-tongued pollinators, and it’s not clear to me how much of a role mimicry and convergent evolution both may have played in European hummingbird moths. The extremely long proboscis of Xanthophan morgani and the correspondingly deep nectar placement of Angraecum sesquipedale is a famous example of co-evolution that had a strong impact on Darwin’s thinking. To my knowledge, there has never been a hummingbird with a 35 cm tongue, and in many ways hawk-moths may have pioneered the lifestyle of deep-seated nectarivory, before it was cool. The fossil records for hummingbirds and hawk-moths alike are rather spotty.

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Xanthophan morgani with extended proboscis from the London Museum of Natural History, by Wikipedia user Esculapio

Equally remarkable is the visual system. Behold those pseudopupils!

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