MadSci Network: General Biology

Re: Why do moths fly toward the light?

Date: Tue Jun 30 09:45:17 1998
Posted By: Neala MacDonald, Grad Student, MSc in Zoology, University of Western Ontario
Area of science: General Biology
ID: 896758081.Gb


As a former entomology technician I know the answer to this question, but could not tell you from what resource I gleaned the information.

Moths tend to congregate around porch and street lights at night for navigation purposes. Now, it is obviously not that productive for a moth to be spiralling around a light bulb in a frenzy of disloged and burnt wing scales - so we need to look at how the behaviour would have evolved originally. Many night-flying animals and insects use celestial light sources to orient themselves in their environment. For example, it is useful to use the light of the moon as a reference point to fly across a corn field if you abide by the rule "keep light ahead, and off of right antennae" early in the night. But when your reference points become as local as a lantern, this can backfire.

It is interesting that in your question you proposed that the location of a light source could be used for reproductive purposes (supposedly as a common meeting place for male and females). I have used black-lights (or UV light sources) to survey moth populations and found the occasional mating pair the next morning, but I suspect this is more opportunistic than anything. NOTE: Re; your query that the purpose of light-navigation is for feeding. I believe that many moths only have mouth parts to collect water, if anything. This life stage generally does not feed (that is the job of the voracious larvae), with mating being the purpose of it's existence. However, many other creatures of the night have learned to capitalize on the disoriented moth clusters during their foraging, particularly bats and nighthawks.

Hope this helps!
Neala MacDonald

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