Posts Tagged ‘light’

Why moths circle lamps, and darkness is our friend

// July 16th, 2010 // 3 Comments » // How Things Work

Sydney Opera House. Image by Froge

I wear my sunglasses at night. It’s for the light pollution. New Scientist today sent out a plea to bring back the night for wildlife’s sake, particularly birds, bats and turtles.

Moths are also at risk to death by light. In Australia, the Bogong moths cause October plagues around Sydney and Canberra. They swarm houses, government buildings, and sometimes land on bosoms of opera singers during the Sydney Olympics (or was that the Hawk moth?)

The reason for the plague is simple, we stupidly built cities near their migratory paths. Every spring the Bogong moth travels from the plains to the mountains, to get away from the heat. They spend the summer lying dormant in caves, aestivating (hibernating in the summer.)

Aboriginal groups would sometimes collect them, cooked they taste nutty and are an excellent source of protein. Unfortunately it’s not an option anymore because they eat stacks of pesticide as caterpillars on the plains.

It’s a common thing to see a moth circling a lightbulb. Why do they do it? They aren’t actually attracted to the bright lights, it’s a mistake in navigation. At least, according to one theory, though there are others I like this one best.

Bogong Moths, Image by Pbpanther

When moths make the migration, they need to know how the hell to get to the mountains. I sail by the stars, but moths fly by the moon. By keeping the moon at a certain angle to the side, they can fly in a particular direction. For example, if you know the moon is in the north and you want to go west, you would keep the moon on your right hand side. I think a similar method was used in Apollo 11, when their navigation systems were down (I’m going by a vague recollection of Tom Hanks following the Earth out the window of the ship.)

It works because the moon is so far away the angle doesn’t change as you move. But imagine you tried the same thing with a street light. If you kept the light on your right, you’d end up going around in circles. Just like moths do.

Some moths don’t fly in circles around light, they just WAP into them. They might be using the same method, but aiming directly for the moon instead of keeping it to one side.

In Adelaide we have trees with lights mounted to shine up on them all night. I would like to know if it damages tree growth or the native wildlife around it. What are your thoughts, and when was the last time you really saw the stars?

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