Saturday, March 21, 2009

A March Moth (Alsophila aescularia) and The Yellow Horned Moth (Achyla flavicornis)

I am an amateur naturalist trying to discover everything that lives in my garden.

In my last posting I described my newly home-built moth trap. I’ve been operating it for only a week, and although we’re still in chilly-March here in Oxfordshire in the U.K., I’ve already ‘discovered’ a further half dozen species to add to the seventy-five living things I’ve already reported on this blog. Normally I give each species its own posting. I’m beginning to think however, not least with summer’s ‘bounteous harvest’ approaching, that it’s likely I’ll find so many night- flying insects I’m going to need to relax this rule if I’m to stand any chance of cataloguing my garden life in a realistic time frame.

Why is it that some - although interestingly, by no means all- species of moth are attracted to artificial light? The late, great moth expert Professor Michael Majerus had a wonderfully concise answer in his book Moths (The New Naturalist Library):

“I do not know”!

A common hypothesis is that moths, some of which navigate by the distant moon and stars, are fooled into trying to navigate by the artificial light. Possibly this is the answer, but if true you might reasonably expect to see moths approaching lamps in a navigational fashion via orbital, in-spiralling flight paths. Watch a moth approach a light trap however, and I have to agree with Majerus, it’s not easy to convince yourself you’re witnessing 'navigation-in-action'. Moths often fly directly towards the light, flutter around it in seemingly haphazard ways, or seem content to settle some distance from it.

Hsaio has put forward (Jour. of Insect Physiology, Vol. 19:1971-76, 1973) an alternative theory that point light sources ‘interfere’ with the operation of moths’ compound eyes causing them to perceive regions of darkness (i.e. good places to hide) around a lamp where there are none. Again, Majerus isn’t convinced. Another of nature’s mysteries! Maybe a reader here has a comment?

To the moths themselves: Firstly, attracted to my light about a week ago, the moth in photo 1. I struggled to identify this one at first, but then caught sight of a photo of The Yellow Horned (Achyla flavicornis), in a slim photo-guide (G.Hyde, British Moths, Jarrold Colour Publications) I’ve had since I was a boy. The larvae (you can find a photo on Ian Kimber's excellent UK Moths site) feed on Silver and Downy Birch from mid-May to July before pupating to over-winter and emerge as the adults found from late-February to mid-April. I read that the Yellow Horned is a member of the Thyatiridae family of moths represented by only nine species in the U.K.

On the same evening, photo 2, a March Moth (Alsophila aescularia), the green larvae of which (again, photo's available on Ian Kimber's site) feed on many broad leaf trees including Oak, Willow and Birch. The adults fly from late February to April and over-winter as a pupae. The March Moth is notable for being one of a small number of moth species where the female is flightless. You can find a photo of a wingless female here.

Why it is that a small number of moths can ‘get away’ with having no wings, whilst all the rest expend precious energy growing them is...yep you guessed it...another of mother nature’s least, it is to me. Comments anyone?


Maggie Watson said...

You're well ahead of me again Henry - I have the bulb, I have a trap, looking rather like yours, and last week I saw a moth fluttering around an outside light and thought now's the time. But I've not yet found the opportunity to get into it all. But I'm happy to follow - I'll see what you turn up! Later in the year I really want to go and find what's in our nature reserve, but that's a fair distance way away (well, 250m) and power is an issue. Will have to get the generator out...

Henry Walloon said...

Make sure you do Maggie and let us know what you find.