Farnley Hall Woods
Farnley Hall Woods, backing on to our Otley garden, are full of moths at the moment although unfortunately almost all are of just one species. From late June onwards my moth trap is dominated by large yellow underwing moths, their numbers this year rising to a recent peak of 350 on just one night, by far outnumbering the other species. The second most common at present are two species of copper underwings (pictured), up to ten at a time, much prettier than the large yellow underwings and almost the only large moth we regularly find in the house, resting on walls and curtains, in contrast to the large yellow underwings which, despite their massive numbers, almost never venture indoors.
The large yellow underwings are good news for creatures that prey on them. Two years ago, on a late summer visit to Minsmere Bird Reserve in Suffolk, we climbed into a canopy hide in an area of woodland. The sills inside the slit observation windows were littered with inch long orange wings with a black terminal band. A notice on the wall explained that these were the hindwings of large yellow underwings. They were falling prey to brown long-eared bats hunting among the treetops which would pick up the moths in flight or from the vegetation on which they were resting. As the moths were too big to eat in flight the bats would carry them to a feeding post, in this case the windowsills of the hide, before discarding the wings and eating the rest.
Having wondered for years as to the identity of the bats above our garden, I have recently bought a bat detector which converts into audible sound the high-pitched clicks emitted by bats during echolocation to avoid obstacles and pinpoint their insect prey. The detector can be tuned in like a radio to the frequency of the clicks giving clues to the identity of the bats responsible. The most obvious are common pipistrelles, emitting calls over a wide frequency range but peaking at about 45 kHz. With them I think are soprano pipistrelles with higher pitched calls and occasionally I have picked up much lower, loud metallic clicks probably from noctule bats.
Frustratingly I have been unable to pick out the very quiet ticking calls of the long-eared bats which surely must be present to feast on the abundance of large yellow underwing moths.
I obviously need some expert help in the identification of these fascinating creatures so my next move will be to join a local bat group.
Denis O’Connor
