Using Light Traps to Catch Insects

A simple insect light trap can be
constructed using these four components.
Photo by Brad Sylvester, copyright 2012

Up until now, for the most part, I have been simply recording the creatures that live in my yard as I find them, one by one. Sometimes, I go out looking for them, and I did use small insect pit traps to collect a couple samples. There's another way, however, to find some creatures that I would otherwise not be able to locate and to collect much larger numbers of species all at once.

What is a Light Trap?

That method involves using light traps. Light traps rely on the fact that many nocturnal insects are strongly attracted to light. By setting up lights to shine on white surfaces, we can induce large numbers of such insects to land on those surfaces. If the surface is slick and slanted sharply, many of them will fall to it's base where a collection bin of some kind can hold them until they can be gathered and examined. The sooner they can be collected, the better.

Many entomologists will line the bottom of the collection bin with poison that kills the collected insects quickly, before the specimens can be damaged by each other, or by struggling to escape. I'm not going to do that. Instead, I'll try to use a collection bin that minimizes such damage. One of the difficulties with live collection bins is catching live insects from the collection bin, without them either escaping once it is opened, or damaged by the collector when they are removed.

Limitations of Light Traps

These kinds of traps can not and will not catch every insect that hits the illuminated collection surface, and certainly not every species of insect in a given area. Some, if not most, will either rebound off the surface and miss the collection bin, or take flight again without falling into the bin. Some will be able to land on the collection surface and remain there due to their adhesion to smooth surfaces being stronger than gravity. Many other insects are not attracted to light at all and will be found in a light trap only by rare coincidence, if at all.

So, the absence of any particular species in a light trap does not mean it isn't there, just that it wasn't caught. Light traps do, however, provide a means of large scale species sampling of a location, and in some cases, can capture hundreds of species of insects in a single night.

The species that are caught by any given light trap will depend upon where it is placed. One placed in an open field, for example, will catch different species than one just 50 yards away in a thicket. There will, generally, be some overlapping species, but many will only be found in one habitat or the other.

I'm going to start with one light trap, placed in the woods. My time and ability to process large numbers of insects for this blog are limited, so I'll use a smaller light collection surface, and I may turn the lights out fairly early in the evening if the trap has accumulated a significant number of species. In any case, I'll post again tomorrow with an overview of the results and then I'll begin adding new species pages as quickly as I can.

How to Build a Simple Light Trap

Equipment:
1 collection sheet (A flexible sheet of white material, smooth plastic works best.)
1 collection bin, (may be almost anything with smooth vertical walls, a jar, for example)
duct tape
1 light source (This may be turned on for hours so use rechargeable batteries or an approved outdoor extension cord)

Figure 1: A small hole leads into the collection
bin. The hole is at least several inches above
the bottom of the collection bin.
Photo by Brad Sylvester, copyright 2012

Step 1:
Curl the plastic so that it forms a small opening inside the collection bin, and the sides conform to the shape of the collection bin. Use a piece of duct tape to hold the collection sheet together, as shown in figure 1.

Step 2:
Use duct tape to pull the plastic collection sheet tight ot the edges of the collection bin so that no openings remain except the one inside the curled collection sheet.

Step 3:

Figure 3: Simple, home-made light
trap for catching insects at night.
Photo by Brad Sylvester,
copyright 2012

Lean the back edge of the collection sheet against a tree or other support, so that it will not fall down in the wind. Place the flashlight so that it shines onto the fron of the collection sheet as shown in figure 2.

Collecting Insects with the Light Trap

Once the collection bin has many insects inside, you can shake the collection sheet to drop any insects still haning on into the collection bin. Then, remove the collection sheet and quickly cover the collection bin.

Converting the Light Trap Collection Bin into a Killing Jar

The collection bin will have a number of insects of unknown species. If you are unsure of the safety of handling the inssects you have caught, or have any allergies to stings or bites, you may wish to convert the collection bin into a killing jar so that the insects are dead before you attempt to handle them. This can be accomplished by using tweezers to dip a cotton ball into nail polish remover and then placing the cotton ball inside a smaller container inside the collection bin. Cover the collection jar or bin immediately.

Depending upon the size of your collection bin, you may need to use several nail polish soaked cotton balls to achieve a concentration of fumes sufficient to kill the insect inside. Allow several minutes for the fumes to take effect. Be sure to avoid inhaling the fumes yourself and follow all safety warnings from the manufacturer of the nail polish remover.