Monday, March 16, 2009

Oak Beauty Moth Biston strateria

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

In my last posting on the Song Thrush I introduced my home-made camera 'trap' and mentioned that this gadget was one of a number I've been cobbling together:

Ladies and Gentlemen, a round of applause please for... (photo 1) ...the Skinner/Walloon Moth Trap!

One of a number of moth trap designs you'll find on the web, the principle of the Skinner trap is simple enough: A lamp to lure the critters towards a box fitted with a 'lid' comprising two sloping sheets of plastic that don't meet in the middle (leaving a gap of about ~1inch) . The moths flutter around the lamp, land on one of the slopes and slide into the box below, whence they aren't smart enough to find their way out. A few egg-boxes give them somewhere to hide.

To best attract moths you need a lamp that peaks towards the blue/ultra-violet. Best is a mercury vapour- or so-called actinic-bulb (you need the correct electronics (a 'ballast') to power either incidentally). I bought the various bits I needed from the Entomological Wildlife Group.

And the result?

After an evening spent excitedly watching my moth trap through my kitchen 2! (In acquiring the photo, I let the moth out of the trap and it alighted on my house wall incidentally).

Twenty minutes spent flicking through my copy of Moths (Waring and Townsend, British Wildlife publishing) and I'm confident I've met an Oak Beauty (Biston strateria).

The Oak Beauty is a member of the Geometridae family of moths of which there are some 20,000 known species with 300 occurring in the British Isles. Geometridae is from the same stem as geometer and is a reference to the measuring, 'inch-worm' gait of these moths in the larval stage. The caterpillars of the Oak Beauty feed on Oak, Hazel, Alder, Aspen, Elm and Sallow. They are well camouflaged to resemble twigs. I've never myself seen one, but you can find a photo of one here.

The moth I caught was a male, as indicated by his impressively large, feathery antennae (close up in photo 2). I personally find such structures a miracle of natural engineering.

Turning to my copy of the superb Moths by (the recently deceased) Michael Majerus (The New Naturalist Library), one thing I learn about the Oak Beauty is that it has a melanic form that occurs in Holland but not in Britain.

For those unfamiliar with melanism: Much as people can differ in their eye colour and yet all remain members of the same species (human'), so some moth species can show considerable variation in their wing pattern. Within one species, some individuals might have patterned wings whilst others might have, say, matt black wings. Careful studies over decades have shown that the places where moths with certain wing patterns predominate are those places where having e.g. black wings is a recipe for good camouflage from predators (say, birds).

The increased prevalence of black winged moths of the Oak Beauty's sister species, the Peppered Moth (Biston betularia), in heavily polluted areas is an extremely famous example of supposed evolution in action (a.k.a. 'survival of the fittest') and consequently has drawn a very great deal of study and heated debate. From everything and anything convincing I've ever read however, the basic conclusion I've drawn is: it's a fact! You'll find no better, more balanced account than Michael Majerus' book above.

Finally, I can't help but end with a comment on the truly wonderful 'folk law' names of moths. The Oak Beauty, The Burnished Brass, The Twin Spot Quaker, Mother Shipton...- the list goes on an on. I commend the following link to one of my all time favourite poems: All These I have Learnt, by Robert Byron.


Suji said...

Henry, we are homeschoolers living in San Jose, California. My son and I are growing to love your blog more and more each day :) Thank you for these wonderful posts. I've nominated you for the Wonderful Blog Award. If you'd like to pass it on to others, please visit my blog. Thanks again :)

Henry Walloon said...


Thankyou very much, I'm flattered.

I enjoyed looking at your blog.

Good luck with the homeschooling.