Monday, October 10, 2011

Two Noctuidae Moths - The Square Spot Rustic and The Setaceous Hebrew Character

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

Some time ago I blogged (here and here for example) my homebuilt mothtrap. I set the trap out in my garden only a few times during 2009 and 2010. So great was the catch however that I'm still working through a backlog of photos of the species I caught (all critters were released alive after being photographed incidentally).
Two species from August 2009 I'm tolerably confident to have identified correctly (with the help of my copy of the Concise Guide to the Moths of GB and Ireland, by Townsend, Waring and Lewington) are a Square Spot Rustic (Xestia xanthographa) in photo 1 and a Setaceous Hebrew Character (Xestia c-nigrum) in photo 2.

The curious Latin species name 'c-nigrum' makes sense when you know nigrum means 'black in colour', hence literally 'with a black letter ''c''' [on its wings]. (Some of you may remember the 'white letter c' butterfly P. c-album I blogged here.)

I've entirely failed to uncover the meaning of the genus name Xestia. Can anyone comment?

Turning to the English common names of moths, I learnt previously that many were invented in the 1730's by the Aurelain society of naturalists.  I'd guess (but don't know) those of the moths here were amongst them.

I needed to look up setaceous. It means whiskery incidentally.

From the book mentioned above I learn that both my moths are common in the UK. Both overwinter as caterpillars. The caterpillars of the Square Spot Rustic commonly dine on grasses, and those of the Setaceous Hebrew Character on nettles and other herbaceous plants.

My attempt to learn a little more about my moths led me to some interesting papers by Chapman [1] and  Wood [2] and The papers describe the authors' efforts to track the migration of insects using ground-based radar. The papers are full of amazing details: I had not hitherto imagined that ground based radar would be so sensitive as to allow tracking of a single grasshopper in flight at a height of 1.5km. Further, as the authors explain, that around the globe millions of tons of insects are aloft at any instant, or that at least 2.3 billion(!) insects were involved in the migrations to/from the UK between 2002 and 2007.

What it is the insects (many moths, including mine, amongst them) are doing at heights of several hundred metres to a few kilometres is taking advantage of high wind speeds to propel them to places of seasonal migration. The speeds are several times greater than that at which an insect could fly unaided. The authors' studies yielded estimates that by harnessing winds insects may be able to travel as far as ~2000km during only three of four 8-hour flights. Things are not as simple as the insects being mere passive 'leaves in a storm' however. Rather, the authors discovered that they exhibit a clear directional sense, flying at an angle to the main wind direction so as to control where they end up. (I suppose an analogy would be a rowing boat in a strong ocean current. Just because the current may be faster than you could row, by sculling at an angle to the main current it's still possible to steer somewhat). How the insects are able to navigate at altitude and at night the papers don't say. I guess the moon may be involved, but that much about how they do so remains a mystery.

1. Flight orientation behaviors promote optimal migration trajectories in high flying insects, J.W. Chapman, R.L. Nesbit, L.E. Burgin, D.R. Reynolds, A.D. Smith, D. R. Middleton, J.K. Hill, Science 2010, 327, p.682-685

2. Flight periodicity and the vertical distribution of high altitude moth migration over southern Britain C.R. Wood, D.R. Reynolds, P.M. Wells, J.F. Barlow, I.P. Woidwod, J.W. Chapman, Bulletin of Entomological Research 99(05), p.525-535, 2009


Paulie said...

Great Blog - right up my alley! I'll be back often!

Paul :)

Carlos M. Silva said...

Just because of an Amblyteles armatorius that i looked for an ID,i found this place,yesterday. Great!And for sure I'll return to help my own id's.
I alredy knew some of yours (british examples! you started early with 'Natural Philosophy'! and that's why is easier for me to find some suitable knowledges in english web) and others like GardenSafari (from Holland) and it's a pleasure and a valuable set of knowledge to get here and learn.
Thank you.
Carlos M. Silva (Portugal)

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