Small Poplar Borer

I'd been planning an early trip to Trench Wood this morning, but the weather forecast told me it was likely to be stormy there, and even though I didn't really believe it, this isn't a place where you want to be hanging out during a thunderstorm, so I decided to postpone my visit until lunch time. So I was still at home, and was able to witness and record the three Large Red Damselfly emergences that took place during the morning in our garden - one from the little patio pond, and two from the wildlife pond.

I was photographing the last of them popping out of its larval case when the sky darkened, and thunder began to rumble in the distance. "Hurry up," I told the damselfly. "You're not ready to get rained on." He was too busy evading me by dodging around the stem on which he'd emerged to reply, and I backed away so that he could concentrate on inflating himself and hardening off. I'm not saying that I'd have fetched an umbrella and held it over him if it had rained, but... well, yes - I probably would. In the event though, the rain held off, so I didn't have to decide between saving a damselfly's life, and preserving what little reputation I still retain among my neighbours as a normally functioning adult.

Trench Wood, when I finally got there, was hot, steamy, and blissfully quiet. I found some nice invertebrates, including butterflies, bees, and a very dashing leafhopper nymph, and I saw an interesting confrontation between an irate sawfly larva and a parasitoid wasp, but as you'd probably expect, I'm going with the creature I'd never seen before. "Woah!" I said, backing up as I caught sight of it on an aspen sapling. "Who are you?!" The answer, when I got home and looked it up, turned out to be Saperda populnea, the Small Poplar Borer - a species of longhorn beetle that creates woody galls on twigs of poplars and willows. I think there's probably a joke to be made here about its common name and the fact that I fond it on a small poplar, but I can't quite be bothered to work it up.

Despite the name, Saperda populnea is actually a fair-sized beetle, at 1-1.5 cm in length (though that's only half the size of Saperda carcharias, the much rarer Large Poplar Longhorn). Females such as this are at the bigger end of the range, and are paler, with more obvious yellow spots and slightly shorter antennae. The smaller, darker males have antennae that equal the length of their bodies. The female makes an incision between the nodes of a willow or poplar twig (the most common host in the UK being aspen), and inserts a single egg. As the larva develops, a symmetrical gall, up to 2cm long, forms around the larval chamber. Pupation takes place within the gall, and the adult beetle cuts an exit hole to emerge in the spring.

In places where aspen is grown commercially, the Small Poplar Borer can be a pest, and there are web sites that give advice on how to control it, but luckily for this beetle, no such measures are likely to be taken at Trench Wood. Aspen saplings are encouraged to grow in abundance on this nature reserve for the benefit of the nationally scarce Aspen Leaf-rolling Weevil, but I can't see any reason why the two species shouldn't coexist.