Fatal Attraction

Researchers shed light on moth mortality

Anybody enjoying the porch at night has probably watched moths bouncing off a lamp. The moths may be a mere annoyance for people, but biologists worry that this “flight to light” behavior has dire consequences for moths and their predators. Now, new research looks into how variations in light spectra produced by different bulbs affect their attractiveness to moths.

“The use of street lighting, security lighting and other urban light sources negatively affected many animal and plant species, and it is considered to be one of the major threats to moth populations,” write five Dutch researchers in Biological Conservation. Many moth species are attracted to light, and some scientists say the moths may be mistaking artificial illumination for moonlight. Since bouncing into bulbs is often fatal for the insects, the researchers wanted to find out which light colors attracted the
most moths.

The team tested six different types of bulbs—including four custom-made lamps, standard white fluorescent bulbs, and actinic lamps typically used in photography and aquariums. Over several nights, the researchers set up moth traps in a nature preserve in the Netherlands and then analyzed the size, weight, and eye size of the moths that succumbed to the flight-to-light instinct.

They found that moths are most attracted to shorter light wavelengths—those near the ultraviolet and violet portions of the light spectrum. The team also found that “artificial light dominated by smaller wavelengths attracted relatively larger moth species and a higher abundance of these larger species.” The findings suggest that areas with more artificial light may have fewer large moths, which in turn could affect the species that prey on the night-fliers. A bird called the European nightjar, for example, feeds mostly on larger moths, so artificial light could be affecting their population by killing off larger moths.

The findings highlight the need for community officials to select streetlamps that attract fewer moths, the researchers suggest. In particular, using “lamps with larger wavelengths to effectively reduce the negative effect of light pollution” could stem the effects of this fatal attraction.

– Matthew Dieter

Van Langevelde, F. et al. 2011. Effect of spectral composition of artificial light on the attraction of moths. Biological Conservation doi:10.1016/j.biocon.2011.06.004.

Image: ©Sjm1123/Dreamstime.com

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