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As Cicadas Invade, Entomologists Have a Field Day

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As I wrote in Salon recently, a large part of the Eastern Seaboard is preparing for an invasion. Not from a foreign military power, but by Cicadas -- in the billions!

Cicadas have black bodies, blood-red eyes and legs, delicately veined gossamer wings and oddly ridged faces that resemble the Klingons from Star Trek. Entomologist Cole Gilbert finds them "amazing." And after listening to him discourse about the species over lunch late last month, I think I understand why. Cicadas (Magicicada septendecim) -- like many of the species Gilbert studies -- are just plain weird.

Cicada Brood 2 is preparing to emerge from the ground as the last act in their 17-year life cycle. Writing about this unique natural phenomenon made me curious about the folks who study insects and their amazing ways. So I asked Cornell's Professor Gilbert what drew him to his unusual profession in the first place. Below is a transcript of our email interview:

What are the special rewards for you of studying bugs -- what gets you excited about the field?

I like plenty of other animals as well. But the diversity of insect morphology, behavior, and life styles is simply amazing. They have been around a long time, at least 370 million years. Some have not changed much, but others that are even younger have changed quite a bit. I often find their adaptations astounding. All animals have the same basic needs: to eat, grow and reproduce. Yet insects do these things in so many different and wonderful ways. Many of them are more bizarre than any science fiction film.

Also, insects are everywhere. They're small, so they fit in anywhere. I advise one graduate student who studies ants in which the whole colony lives inside a single acorn. Their entire home range might be less than 5m x 5m in the woods. Most people don't notice most insects, because humans tend not to notice or be attracted by the small things. But they are present and can be studied anywhere. I have spent a lot of time in wild places in the Neotropics and been fortunate to lead ecotours to many exotic places around the world, but there are myriad fascinating and untold bug stories playing out in my 8 acre woodlot just out my back door in central New York state.

I also like it that insects have abilities that we don't have. For instance, most insects can see the plane of polarization of light. We can't. This isn't just a simple issue similar to their ability to see ultraviolet wavelengths and we can't. Polarization is a fundamentally different property of light from wavelength and we do not perceive it. Thus, when we see a clear blue sky, insects see that too, but they also see concentric bands of polarization circling the sun increasing in intensity as the angular distance from the sun increases to about 90 degrees; then the strength of the bands diminishes. This is obvious to them all the time. It is screaming out at them whenever a bug goes outside and looks up, but we just see uniform blue. And many insects, such as bees and scarabs beetles, use this pattern to navigate in their world.

It makes me really happy to think about different creatures inhabiting the same physical world, but perceiving it fundamentally differently because of our different sensory equipment. The great Japanese filmmaker Akiro Kurosawa approached this topic in his film Roshomon. But thinking about insects takes it to a completely different level. It leads to a sort of Zen appreciation to try to imagine their world.

Could you describe what you will look like, what equipment you will be bringing, what exactly you will be doing in the field when the cicadas come out?

We will be wearing field clothes, a little grubbier than what I wear when I lecture, but nothing extreme. We will collect lots of cicadas and keep the males and females in separate polyelthyene tubs. Then we'll measure off 50 meters with a tape measure from the woodland edge of the aggregation and set up a station. There we'll use a microphone and digital recorder to take measurements of sound intensity in all directions, probably at 15 degree intervals. We'll toss cicadas individually into the air, watch them fly until they land or vanish in the distance, and record their directional bearing. We will repeat this procedure at increasing distances from the woodland edge. I don't have a sense of how far out we will need to go, but I would like to go so far out that the cicadas fly in random directions from the release station.

From comparison of those data we should be able to answer the question of how loud does the cicada swarm need to be for an emerging cicada to locate it, fly there, and thus gain some protection from predators (because of the sheer numbers of cicadas) and possibly find a mate. This will also provide some evidence about the effect of habitat loss and fragmentation on cicada populations.

What are some of the main questions that you and other entomologists will be working on relative to the cicada population?

I suspect that some folks, especially the group in Connecticut, will be mapping closely the distribution of populations on the edge of the brood in Connecticut. We need such fine scale mapping to more directly understand the causes of shrinking distribution of cicadas who are mysteriously vanishing from some areas of their previous range. I'm not sure what other researchers will be looking at.

You mentioned that climate factors may be responsible for their decline -- will yours and others research possibly give some clues about this?

The Connecticut group published a habitat modeling study a couple of months ago that incorporated climatic variables. Their models indicated that temperature, rainfall, and seasonality were stronger predictors of where cicadas could be found were than was fragmentation or land cover (e.g., loss of forest). Unfortunately, most large-scale modeling like that does not have fine-grained climatic information, which they discuss in the paper as a limitation. Thus, I suspect that they will be trying to get such data this summer, if only as a baseline for comparison with 2030. My experiments this summer will not explicitly address the effect of climate.

What do you tell your students about why it might be a good thing to become a professional entomologist?

At Cornell we train undergraduate entomology students broadly in biology and deeply in entomology. Thus, they can get any kind of job that a biologist can get. I have worked up-- with apologies to David Letterman-- my Top 10 list of reasons to study bugs. Because species of insects are so numerous, there is hardly any question in biology that you might ask that could not be favorably approached working on an insect... There is no end to interesting and important questions that can be addressed with insects from basic biology to human health and agriculture.

As I reported in Salon, "like so many other of earth's creatures, cicadas may be ill-equipped to endure the seismic shifts in the climate system that have already begun to happen. But until more information is gathered, this is only a guess." The data gathered by entomologists in coming weeks will help to throw some light on the effect of climate change on one of America's most fascinating insects.

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