Moths by Michael Majerus

Author:Michael Majerus [Majerus, Michael]
Language: eng
Format: azw3
Tags: Nonfiction, Reference, Nature
ISBN: 9780007406739
Publisher: HarperCollins Publishers
Published: 0101-01-01T00:00:00+00:00

Unfavourable weather

The weather that may adversely affect moth survival can be thought of as either active weather or passive weather. By active weather, I mean weather that has direct physical force, such as strong winds or the impact potential of hail or large raindrops, or even the force of surface tension of a still water body. By passive weather, I refer to high or low temperatures or abnormal humidity levels.

It is not difficult to envisage the potentially disastrous effects that active weather may have. In high winds, larvae may be blown from their foodplants. Particularly in tree-feeding species in which egg hatch occurs around the time of bud-burst, young larvae that hatch prior to food being available will hang on silken threads to be carried by the wind hopefully to an earlier leafing tree. However, in strong winds, such larvae may be carried far from any appropriate food.

Heavy rain or hail may be a hazard for flying moths in two ways. First, the impact of heavy raindrops or hailstones may cause damage. Second, such impacts may knock the moths to the ground where there is the risk of landing in puddles or on wet substrates where the surface tension in the large area of contact between water and wing surfaces may be too great for the moth to pull away from. After heavy storms on warm summer nights, examination of puddles in the morning often reveals a considerable array of dead or dying moths stuck on the surface.

Given the risk of flying during heavy rainstorms one might suppose that moths would seek shelter and rest up during downpours. However, this is certainly not the case for many species. In 1992, due to timetabling constraints of a field course, I had occasion to set up six Robinson mercury vapour moth traps behind a dune system near Wells-next-the-Sea on the Norfolk coast, on a night (22 July) when thunderstorms were forecast. The traps, run off portable Honda generators, were operated from 9 p.m. until just after midnight. The storm that arrived was not a run-of-the-mill storm. In just over three hours we had 37 millimetres of rain and, at the height of the storm, lightning flashes were coming at the rate of 14 per minute. Yet, amazingly, many species of moth were flying in good numbers. The full list of the catch from the six traps is given in Table 7.1. That several large species were flying is perhaps not surprising. Pine Hawk moths, Hyloicus pinastri, Oak Eggars, Lasiocampus quercus, and Drinker moths, Philudoria potatoria (Plates 4c and 4d), together with some of the more robust noctuids, would probably have the size and power to shrug off the wind and water. However, I was amazed that many geometrids were also flying, even during the strongest rain. Although some of the smallest geometrids were neither seen nor caught, suggesting that some species, such as the pugs and smaller waves, were deterred from flight, the results suggest that rain is not a flight-limiting factor for most species of larger moth.

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