This article was published in Scientific American’s former blog network and reflects the views of the author, not necessarily those of Scientific American
Eran Levin is a postdoctoral researcher at the University of Arizona. His research is with hawk moths, but catching them means that he gets to see a plethora of other critters. Here he shares how blacklighting works, alongside some photos of it.
Hawk moths are among the best flyers in nature. Their very strong flight muscles, physiology and aerodynamic ability makes them perfect flying machines and enable them to fly long distances at high speeds. Like most of the other moth species (about 160,000 known species of moths), hawk moths navigate by bright objects- usually the moon and stars. By keeping these objects at a constant angle they can keep a straight course.
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Artificial bright light, like a light bulb, will interfere with the moth’s ability to detect moonlight. Instead the moth will try to keep this source of light at a constant angle. Due to the relative close distance to the light bulb it attempts to navigate a straight path by the artificial light that ends up as the moth caught in an endless spiral around the light bulb (or in case of fire- in the flames).
This behavior is common in many nocturnal insects like beetles, moth, lace wings, bugs and more. Entomologists use this behavior in order to “trick” the insects into traps. In order to collect nocturnal insects they use a “light trap”: a white sheet which reflects the light and also giving the insects a surface to land. The light source for the light trap is usually a powerful mercury vapor bulb. This light bulb produces visible light in the range of blue- white color, but also produces UV radiation. Unlike humans, many insects can see UV lights and they are attracted by this wavelength. In many cases, entomologist add some pure UV neon light to their light trap that helps attract insects. The UV light is very often referred as “black light” as we actually can’t see it.
When using the light trap it’s best to choose a place with minimum light pollution, and on a night with no full moon. Where I work in Southern Arizona, during the summer time people from all over the States come to collect insects at night. This is one of the hotspots for hawkmoth diversity outside of the tropics.
Article and photos by Eran Levin