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September 21, 2020

Red light, No light

By Eli Baskir, Manager of Behavior Sciences

Think about the length of your average Saint Louis Zoo visit. Then, consider how long keepers and other Zoo staff are present on site--somewhere between 8-10 hours, depending on their exact job. These schedules mean that humans are only at the Zoo for about a third of a 24-hour day. Once all the guests and keepers head out for the night, what are animals doing with the rest of their day?

After the keepers go home, nocturnal species are just getting started! As these animals strongly prefer to move under cover of darkness, we can't leave lights on to watch them. Instead, we use cameras and special lights for overnight filming. In the Bayer Insectarium, we are trying to learn which combinations of color and bulb will least affect nocturnal insects—in short, under which lighting type will insects act as if they are outside at night?

While humans see wavelengths of light in what's commonly known as the visual spectrum—from long wavelength red to shorter wavelength violet—other animals have different sensory capabilities. For example, many insects are attracted to ultraviolet light; plants that rely on bees for pollination will often have special "pollen guides" that can only be seen under ultraviolet light.

On the other end of the spectrum is infrared light, which, just like ultraviolet, cannot be seen by humans or by many other species. Most video cameras can record footage under infrared illumination, which makes it a good choice to use for night filming. But using infrared light also has limitations. Images filmed under infrared are recorded as black and white, and the light also relies on hard surfaces from which to bounce and fill an area, so filming outside or on a soft substrate can result in dim, fuzzy, unclear images.

Bulb type is also important for filming. While using an LED at home can be good for energy bills, it also gives off less heat than incandescent bulbs and has other qualities that make an LED a better choice to use for overnight filming. We are still learning about how different species react to LED illumination when compared to incandescent bulbs. Some insects seem to be unable to see red light—especially red light from an LED—which could make this combination of color and bulb type very useful for overnight filming.

To test how red LED illumination affects the activity of nocturnal insects, we performed an experiment with dragon headed katydids. Keepers barely see this species move at all during the day, but we know they move and eat at night, since keepers arriving in the morning find chewed food and katydids in different positions. We compared the movement and behavior of three katydids during a 2-hour period starting at noon to another 2-hour period starting at midnight. While the "noon" observations occurred under the normal fluorescent lights of the Insectarium, the "midnight" observations took place over five evenings when two red LED bulbs were the only source of light for the katydids.

Our observations showed that these normally inactive and immobile insects will move and climb all over their habitat at night as they perform many active behaviors, such as eating and cleaning themselves. While we don't yet know for certain if katydids can't see the red light or if they can see it and don't react to it, it does seem like the activities we filmed are similar to what we would expect to see from katydids in darkness. We are hoping to expand this study by observing other light-sensitive insects. Some of the possible subjects live in burrows or in other areas that are difficult to film, so we are currently consulting with Insectarium staff, builders from our Facilities team, and other experts to develop the right kind of set up to collect footage from reclusive animals.

Photo: Dylan Cebulske

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