News - July 7, 2011

Artificial light attracts large moths in particular

Excessive light at night affects the natural living environment of plants and animals, but there has been little research as yet on how and why. Now Wageningen researchers have managed to unravel a small part of the mystery. The group headed by Frank van Langevelde (Resource Ecology group) and Dick Groenendijk (Dutch Butterfly Conservation) investigated what kind of light moths were most sensitive to.

Moth traps were set up in the De Kampina nature area in Brabant province, together with six different kinds of light: a conventional light and lights specially designed by Philips emitting light in certain wavelengths ranging from 380 to 610nm. Moths turn out to have a strong preference for the shorter wavelengths - light with a great deal of ultraviolet in the spectrum.
Not only do the traps with shorter wavelengths attract many more moths, they also attract many more different species of moth. That difference can be up to a factor seven. This preference for UV light is not new, but the study is the first to give precise details of the effect.
What is new is that not all moths are attracted to the light to the same extent. It appears that larger moths in particular are more likely to gravitate towards the light. Van Langevelde: 'Larger species that are heavier, with longer wings and larger eyes, prefer the shorter wavelengths, and that is surprising.' It is not known why that is. 'We have made the observation but do not yet have an explanation.'

Disruption to the food web
But according to Van Langevelde, this observation has far-reaching ecological consequences. Streetlamps at night serve up a feast for hunters such as bats that prey on moths. In this way the larger species in particular are being taken out of the moth population. That in turn affects birds that feed their young on the caterpillars of these larger species. As a result, the food chain is being disrupted. Declining moth populations also affect the pollination of plants. 
Van Langevelde says insect monitoring will also have to allow for the wavelength effect from now on. Van Langevelde's research is part of a large study of the effects of light pollution on plants and animals. Wageningen UR is collaborating on this with Philips and Dutch Butterfly Conservation.
Source: Biological Conservation (2011), online, soon to appear in print