Speaking of Nature: Ever heard of an exuvia?: A triumphant use of unexpected science vocabulary

The word was “exuvia” and those of us that heard it were overcome with a mixture of surprise, confusion and skepticism. The person who dished up this scientific morsel was Brian Adams, professor emeritus of environmental science at Greenfield Community College. The setting for such an utterance was a radio studio at WHMP in Northampton, where I was sitting for an interview with Brian, Bill Newman and Buz Eisenberg on their wonderful “Talk-the-Talk” program on July 23.

Our conversation was centered around a photograph in last week’s paper that featured a fragrant water lily with a spreadwing damselfly clinging to one of the petals on the left-hand side of the photo. I then called everyone’s attention to a yellow “smudge” on the inside surface of the very same petal that was supporting the damselfly. This, I explained, was the shed skin of a damselfly nymph that had crawled out of the water, freed itself from its shell and abandoned it in order to start its adult life. Everyone was looking at the photo and then we heard “exuvia” in our earphones. It was Brian who had offered up the term out of nowhere.

As luck would have it, we were right at the point in our segment where it was time for a commercial break. The microphones went dead and every cellphone and computer in the studio was immediately activated for our combined mission to fact-check this spontaneous utterance. Was Brian a genius, or a complete lunatic? In seconds, the answer to our question was settled: Genius! Bill Newman read the search results and the studio (and the first moments of the second half of our segment) erupted with exuberant, triumphant and congratulatory laughter.

Here is what our search found: “In biology, exuviae (singular: exuvia) refers to the shed exoskeleton or outer covering of an arthropod (like insects, crustaceans, and spiders) after molting. Essentially, it’s the ‘skin’ they leave behind after growing.” Examples of this structure included cicadas and dragonflies. Jackpot! I went on to explain that the photo of the water lily was meant to show the flower, rather than the insects, but it was true that I could have zoomed in on the exuvia to reveal its details. Sometimes, a single photo has so much going on that you need to make a choice.

But, as the interview continued, I very clearly remembered a photograph that I had taken years ago while standing on the edge of a small pond. Thanks to my obsessive cataloging of my photos, I was able to enter “dragonfly” into the search field of my own database and a photo with the description “dragonfly skin” was the third item on the list. In less than 20 seconds I had the image up on my screen and I was ready to go.

So what we see in today’s photo is the exuvia of a large species of dragonfly. The nymph that may have lived underwater for a couple of years had finally reached a point where it was time to crawl up out of the water, break out of its skin one more time, and take its adult form. It is not clear in this particular photo where the exact location of the split on the nymph’s dorsal surface might be, but the presence of those white “strings” gives a hint. These white structures are called “tracheae”: which are “the internal air tubes that insects use for respiration, essentially their ‘lungs.’” Imagine pulling off your socks and having them turn inside out and you have the right idea.

The photo that showed the details of the exuvia did not show you what the plant itself looked like, so I decided to create a composite image that combined the details of two different photographs. The insert shows the blossoms of the flowering rush (Butomus Umbellatus) that the dragonfly nymph had chosen to climb. I didn’t have room for the plant’s leaves, nor for the shape of the “umbell” formed by the plant’s many flowers, but I think the detail of a single flower was the most interesting. The plant was about 4 feet tall and growing in shallow water. I took these photos on July 25, 2011, and have only just now found an opportunity to use them in tandem.

Next week I am going to introduce you to a gorgeous member of the dragonfly family that I discovered during a low-speed boat tour of a gorgeous New England lake. I will focus on the life history of dragonflies (and their allies) and then I will offer some suggestions for good places to go and look for them for yourself. Then, the rest of August will be dedicated to the plants that live in bogs. We have some wonderful bogs to explore right here in western Massachusetts, so it might be time to prepare yourself for a picnic expedition with friends and family.

Finally, I would like to thank Brian, Buzz and Bill for being such warm and generous hosts. I genuinely look forward to my annual appearance on Talk-the-Talk because these guys are simply fun to spend time with. If you would like to hear my July 23 interview, then just head over to my website (www.speakkingofnature.com) where you can find a link that will take you directly to it. Until next time, keep your eyes and ears open for Nature’s many wonders.

Bill Danielson has been a professional writer and nature photographer for 28 years. He has worked for the National Park Service, the US Forest Service, the Nature Conservancy and the Massachusetts State Parks and he currently teaches high school biology and physics. For more in formation visit his website at www.speakingofnature.com, or go to Speaking of Nature on Facebook.