At the light

Entomologists use a variety of techniques to capture insects. The most well known are butterfly nets, which can be used to scoop up just about anything that moves. Nets can be made with thin mesh, thick mesh, super long poles, baited with pheromone lures, you name it. And then there are pan traps, burlese funnels, malaise traps, sticky traps, bait traps… a nearly endless array of creativity. And one of the best ways to collect insects at night is to let them come to you.

It isn’t fully known why so many insects are attracted to lights, but they are. It may interfere with their navigational systems, and once they’re on the sheet they think it’s day time (so they default to their day time resting behaviors).

Many techniques fall under the umbrella term of “black-lighting”, even if you don’t use an actual black-light. They work quite well (even the ones you find in a party store), but even more powerful are mercury vapor lights (and much more expensive). A light, or combination of lights, are hung in front of a large white sheet, and… that’s it. The waiting begins. The set-up can be elaborate with frames and multiple lights, or as simple as a sheet thrown over a branch with a party light. I personally hang a small black-light from the outdoor light on my back patio, and clothes-pinned a sheet to the siding.

At the research station in Arizona (where the above photo was taken), we had several different black-lighting setups throughout the grounds. Some were closer to the stream, some by the buildings, and some were farther out in the woods. We also traveled to different locations in the forest and the desert and set up black-lights there.

Only certain species are attracted to the lights, and they come at different times of night. Sometimes only one sex comes in, meaning the other sex is virtually unknown or uncommon in collections. And the timing means that you might have to stay up until 3am to get the species you’re looking for. If you’re lucky, it will cooperate and come in before midnight!

What you need to collect insects at night

  • Black-light or mercury vapor light, and a power source. This could be an outlet if you’re near a building, a battery, or a generator. Make sure the light you buy is compatible with your power source!
  • A white sheet. Anything with patterns or colors will make it difficult to spot insects.
  • Ropes and clothes pins. These all depend on where you want to hang your sheet.
  • Collecting jar. If you want to keep things alive for observation, any container will do. If you want to kill your specimens, use a cyanide kill jar or a plaster jar charged with ethyl acetate (you can also put a jar of insects in the freezer). Keeping a bit of tissue or paper in the container will prevent the insects from running around.
  • Headlamp or flashlight. You’re outside at night, after all.

Some tips

  • Hang the light away from the sheet. A few inches to a foot away is ideal. This prevents your sheet from overheating and allows for more reflection on the sheet.
  • Keep the sheet steady against the wind. Hold down the bottom with rocks, and generally stay out of windy areas.
  • Many types of equipment can be bought through BioQuip. If you’re looking for cheaper materials, try Amazon.
  • Only collect where it’s legal. Ask for permission to use land, and get collecting permits when needed.
  • Consider the time of year. Things are winding down here in the North East, but you need to figure out when your target species will be out and about.
  • Be patient! It’s good to go black-lighting with friends (and maybe alcoholic beverages).

A cute little mantisfly on a sheet in Arizona.

Posted on September 13, 2011, in Arizona Lep Course, Invertebrates. Bookmark the permalink. Leave a comment.

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Ryerson Lab

Functional Morphology, Sensory Biology, Behavior, Biomechanics

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Trying to make sense of the world through science and language.

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