Batesian mimicry.

June 09, 2023  •  Leave a Comment

Regular readers of this blog may already know that we're NOT arboriculturalists, so are happy to have a thriving colony of hornet moths in our back garden black poplars.

Every June these moths erupt from the subterranean roots around our biggest poplar in particular, break free of their pupal case and quickly climb up the tree trunk (or ivy frond, or long grass stem nearby) to pump out their wings and begin their short adult life.

The males will pump up their wings, get rid of a lot of fluids built up in their body during their time underground in the tree's roots and then fly immediately if possible to a newly-emerged female - to mate her.

The bigger females will pump up their wings and then start to emit pheromones into the air around them. Powerful things are these chemicals - and within minutes of emerging and starting to emit their pheromones, the females will be mated after a passing male (or more often than not, a recently-emerged male from the same tree, on the same day in fact) homes in on that chemical attractant.

Mating is a long, drawn out affair (two adult moths can be linked together for an hour or more).

Eventually the pair will break their abdominal bond, the female will lay her eggs on a suitable substrate nearby (often the same tree roots that she emerged from) and the male will disappear.

Like many insects, the vast majority of the hornet moth's life cycle is spent as a larva - two or three years in fact, as opposed to perhaps two or three days as an adult, winged moth.


We're lucky to see these beautiful moths in the garden each June. Very often it's quite hard to see the adult hornet moths (that is to say if you *don't* have a colony in your garden) as they pupate quickly, scamper up the poplar tree trunks, pump their wings up and fly up into the canopy lickety-split.

Hornet moths also really are quite picky moths. Not every black poplar hybrid tree will do. They tend to demand older trees, often on their own, in full sunlight with a lack of ivy or long grass or nettles around the base of the stump (so they can lay their eggs easily and emerge easily into sun). These sorts of trees tend to occur on private land (private gardens, perhaps parks and golf courses - that sort of thing - areas of land that have kept their black poplar hybrids and MOW around them each year).

We have such a big black poplar hybrid. Which they love. 

They'll kill it eventually of course, but we've been growing a few more now for a decade. These younger trees we've grown are as tall as the older, mother tree now (poplar spreads and grows quickly if allowed to).


Each June I am very aware that these beautiful moths will start to emerge from the roots in the back garden, so I put myself (and my eldest boy, often) on red alert.

On a suitable June morning, around 8am-9am, if the conditions are right, (warm, sunny if possible, a lack of wind if possible), they'll emerge. Sure as clockwork.

This morning I was working from home, in the dining room, from which I can see the back garden (through the conservatory).

I had done a quick recce of the tree around 9am and couldn't find any shed pupal cases - so went in and carried on with my work - vowing to check again in an hour or so.

But at half-past-nine, I noticed three or four loud magpies dancing noisily around the base of our biggest poplar.

I KNEW what that meant.

The moths were erupting from the ground.

Magpies and great tits, as it happens, take no notice of the Batesian mimicry of the hornet moths. They aren't fooled and LOVE to eat these plump, juicy insects.

The hornet moth's scientific name is Sesia (moth) apiformis (bee-like) - despite them looking far more like hornets and not bees.

The strange thing is (I think, anyway) is that this mimicry is sublime in hornet moths. I mean, not only do they look just like hornets, they buzz like hornets too and even dangle their legs when they fly - just like hornets. Clever birds, magpies. And great tits too!

So... out I ran. To the big tree. With a camera or two.

The below is what I saw...

Have a lovely weekend, grapple fans. I hope the forecast storms miss you (if you'd prefer that) or smash right into you (if, like us, you probably need the rain after four weeks without).




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