Dear Readers, when I saw this insect flying around the buddleia in St Pancras and Islington Cemetery, I took one glance and cheerfully told my friend that we were looking at a hornet. Well, clearly I was having one of those days because when a second insect joined the first one, I started looking around a little anxiously in case we were standing close to a hornet nest (though these are actually remarkably serene animals, much less likely to sting you than your average wasp). And then, light dawned. This is, of course, a hornet mimic hoverfly (Volucella zonaria), about which I have written many times before.
How can I tell? So many, many ways, readers, all of them forgotten in the excitement of the moment. Firstly, flies only have two wings, hornets (and all wasps, bees and flying ants) have four. Secondly, look at those big compound eyes! Bees and wasps have much smaller eyes which are often almond-shaped. The antennae are different too, and the wings are carried differently. The hoverfly is a pretty good mimic, and I’m sure a hungry bird would give it a pass, but as a budding entomologist I should have been a little more circumspect.
Incidentally, telling the sex of a hoverfly isn’t easy in all species, but it is in this one: if the eyes meet at the top of the head, the insect is a male. If they’re separated by a yellow band, as in this insect, it’s a female. To reproduce, she will walk cheerfully into a wasp or hornet nest and deposit her eggs – it maybe that her stripes help to fool the residents, or maybe they simply aren’t bothered as the larvae, when they hatch, perform a useful service – they live on the debris at the bottom of the nest, and may even eat the larvae of other insect pests that live there. When the nest starts to break down in the autumn the larvae leave the nest and pupate, normally in the tree cavity where the nest was positioned.
Hornet mimic hoverflies are migratory, with the population of locally-born flies being reinforced by insects from mainland Europe every year, and some flies making the return journey in the autumn. Insects often look so frail, and yet they are capable of extraordinary journeys. Furthermore, after bees hoverflies are our most important pollinators – although they don’t collect pollen deliberately, as they don’t rear their young, pollen grains nonetheless attach themselves to the fine hairs that cover their bodies, and are hence transferred from one flower to another. And honestly, what a magnificent looking insect this is! I have a great fondness for ‘real’ hornets, but this creature also has a place in my heart.