Moths - seeing the light

2011-09-29 00:00

IN recent times I have become aware of the fact that moths live precarious lives. For example, there is a large supermarket in Pietermaritzburg that is regularly inundated by moths. When alerted to the last infestation, I investigated and found not only large numbers of moths, but representatives of a wide range of species being attracted to the shop’s bright lights. This suggested that the explanation for their numbers was not a mass emergence by a single local species or the passing of a migratory swarm.

Many moths are seasonal and emerge at the end of summer because their feeding caterpillars require most of summer to develop. Exactly what triggers their mass emergence is not well understood, but the phenomenon probably ensures that males and females find each other and so secure the next generation.

Why moths are attracted to light is somewhat of a mystery. Most moths are nocturnal and often go to great lengths to avoid daylight. An old theory, now largely discredited, suggests that moths use moonlight to navigate and that artificial sources of light completely disorientate them. Whatever the explanation, it is a fact that moths are attracted to our lights and that this usually has a negative impact on them. Not only could the source of light be a flame that could burn them, but there are other perils that await them.

Apparently, the supermarket’s response was to call in a pest controller who would no doubt use an insecticide. Moths arriving at the supermarket in the late afternoon attracted the attention of a variety of birds that enjoyed them as an evening meal. Many of the moths I encountered were weak and could not defend themselves from attacking ants that were literally tearing them apart and toting them off to their larders.

Clearly, to be attracted to the bright lights of the store was not in the best interests of many of the moths I encountered that evening. As a conservationist I could not help thinking that something needs to be done to safeguard future generations of moths and that the problem could easily be solved by the installation of lights that do not attract them.

It is well known that insect vision is not the same as human vision. Many insects can see ultraviolet (UV) light while humans can’t. In fact, it is common knowledge that many insects are attracted to UV light and, indeed, lights emitting high levels of UV have assisted entomologists who study nocturnally active insects. So, if your lights attract a lot of insects, consider installing bulbs that emit low levels of ultraviolet as this action would undoubtedly help conserve our wildlife.

Most KZN residents, especially those in our more subtropical areas, are familiar with the house gecko (Hemidactylus mabouia), a nocturnal predator that is commonly found around our lights. These lizards are not endemic to many of the places that now support them. Perhaps the most important factor that has led to their range expansion is our ability to generate light during periods of natural darkness.

As discussed above, many insects are attracted to artificial sources of light and so geckos have found it easy to muscle in and are making a very good living in and around our houses. I believe the impact that geckos are having on our local moth populations must be enormous. Again, from a conservationist’s perspective, this is bad news as this kind of impact on our biodiversity is something we should be trying to curb. I think it is time that we humans see the light and take appropriate action.

If we are serious about caring for the creatures we share our concrete jungle with we must start by installing lighting that does not attract insects.

• Dr Jason Londt is a natural scientist with a special interest in entomology. He welcomes queries and comments, which can be sent to him at jasonlondt@telkomsa.net

 

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