Tuesday, 17 June 2008

Flying to the moon?

Tonight the weather forecast is for clear skies. There is a full moon and the clear sky will mean that the temperature will drop to about 11 or 12 deg C, and the wind is also picking up. All these things combined will probably mean that there will be very few moths in the moth traps tomorrow morning. I guess that the relationship with the cold temperature is obvious, after all butterflies are less easy to see in cold weather, all insects need warmth to get the energy to fly. However the link with the moon is less clear. Why do moth fly towards lights or fires? First there's phototaxis, this is an organisms automatic movement towards, or away from light. Cockroaches are negative phototactic animals whereas moths are positively phototactic. Some moths are migratory and it s thought that they use the features of the sky to navigate. Many lepidopterists suggest that moths use the moon as a primary reference point and can actually calibrate their flights by it. There is even evidence that moths have an internal magnetic detector to help them navigate. So a moth's attraction to an artificial light or to a fire could be related to orientation, and lead to disorientation -- the moth wasn't "expecting" to actually get to "the moon" (the light source) or to be able to fly above it, so confusion results. Moths are more sensitive to some wavelengths of light, ultraviolet, for example, than they are to others. A white light will attract more moths than a yellow light. Different sorts of bulbs in moth traps seem to have different successes on different nights, but so far I've not found any consistency in which moths go to which lights.

1 comment:

John Young said...

Nice post Tony. Been my best year for wainscotts in Longfield this year, normally don't catch any. Trap will be out tonight if the rain holds off.