Posted by: Ross Gardner | July 19, 2015

Masters of disguise

A visit to the RSPB’s and Cambridgeshire’s Fowlmere nature reserve this weekend and an encounter with something a bit special.  It is a return to the world of moths once again, but what a superb creature.

The beastie in question is a Lunar Hornet Moth and a species that I had never seen before.  Indeed, while a common enough species, the adults are rarely seen.  If the imago proves elusive a knowing eye might instead discover the signs of the larvae or emerging adults.  The caterpillars feed and pupate low down in the trunks of willows and poplars in which their exit holes can be seen and piles of sawdust-like droppings (frass) might be seen on the ground beneath.

It was well worth a few decades of waiting to lay eyes on a freshly emerged adult.  Walking along a boardwalk beneath a canopy of sallows, a flying insect caught my eye up ahead.  I was expecting to find a longhorn beetle, such was loping nature of its movement through the air and dropping onto the low vegetation.  I was mildly surprised to discover, a first glance at least, that it was a Hornet, but hang on a minute……!

The differences between wasp and moth are obvious enough once a more considered observation is made.  The head and eyes of the latter are noticeably smaller and it also, of course, lacks the ‘waisted’ appearance of the former.  It is nevertheless, a wonderful example of Batesian mimicry, whereby a harmless animal evolves the appearance of something more dangerous and thus benefits from that others bad reputation with any would-be predators.  It is named after Henry Walter Bates, a 19th century naturalist who travelled Alfred Russel Wallace (that naturalist whose own discoveries and line’s of reasoning ran in parallel with Charles Darwin’s) and is particularly well-known for his studies on the mimicry of insects in the Amazon rainforest.

A fine figure of a moth which I’m sure Bates himself would have been impressed by.

Lunar Hornet Moth (Sesia bembeciformis).  Copyright 2015 Ross Gardner.

Lunar Hornet Moth (Sesia bembeciformis). Copyright 2015 Ross Gardner.

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