A Neotropical Nomad in the Sonoran Desert

Jon Hoekstra, currently of the Center for Aquatic Ecology, Illinois Natural History Survey, Champaign, IL, was a graduate student at the University of Arizona, Tucson, who earned a master's in entomology. His primary interest is the ecology of larval aquatic insects. During 1996, he was studying the larval ecology of the recently described Argia sabino Garrison. After learning to recognize members of this complex genus, he went looking for populations of A. sabino in the far reaches of Sabino Canyon and beyond. He has successfully recognized a large percentage of the Odonata occurring in southern Arizona.

Our amazing story starts on 11 August 1996. I had received a parcel from Jon. Upon opening it, I saw a single pinned, male of a clear-winged Palaemnema. The strange part was the label accompanying it: ARIZONA: Cochise Co., Hot Springs Cyn., 11 Aug. 1996, J. Hoekstra. Nooo, I thought, this must be some kind of a joke. No member of this genus, — in fact, no member of this family, — was known from the United States. Most of its members were known from the moist rainforests of Mexico and Central and northern South America. Yet the solitary male seemed paler than any other Palaemnema I had ever seen. Within the next two days, I belatedly examined my e-mail messages (which these busy days with my two children and work always seem to mount up on my computer). Two messages were from Jon. The first asked if I could identify the specimen he sent me since he did not recognize it. His second told of having seen the new damselfly manual by Westfall and May and, from his recollection, he opined that his specimen was a Palaemnema. A Palaemnema it definitely was, but I could not yet place it to any particular species.

My next step was to notify Dr. Thomas W. Donnelly of New York, because of his extensive knowledge of and interest in this genus. I also wrote to Jon, suggesting that we take a short weekend trip to the locality to see if we could discover more of these insects. I received a favorable reply. Jon proceeded to obtain official permission to collect at the site, while I arranged to fly out for the weekend of 20-21 September, a scant 40+ days since the original find. Would we be lucky enough to see more palaemnemas? We both hoped so, for Jon told me that he had seen at least two more individuals on 11 August. After I flew to Phoenix, borrowed my parents' car and arrived at Jon's house on Friday night, we discussed his remarkable find at further length. On August 11, it had been drizzling—certainly not good conditions for collecting adult Odonata!

Muleshoe Ranch Nature Preserve is an isolated, out-of-the-way paradise owned by the Nature Conservancy at the southern end of the Galiuro Mountains. A 15-20 mile dirt road west from Willcox leads to this little-explored locality. As the settlement name implies, there are various hot springs, a perennial water source. We arrived at about 10:30 am on Saturday. Already the cool night air was vanishing, and the scorching sun, we could tell, was about to rule the day. We were both excited, but I did not realize that a two-mile trek to the capture site was necessary, and I was wearing irrigation boots (not recommended for hiking!).

Along the way to the Preserve, we were greeted with intermittent patches of water and flowing stream broken by stretches of dry, sandy arroyo. The stench of rotten eggs wafted occasionally through the air, alerting us to the unique nature of this area. Odonata were there aplenty, but we found nothing spectacular along the way. We were also in a hurry to get to "the spot."

Finally, Jon exclaimed, "This is the spot." We could tell that it was fall by the angle of the sun. It was about 2:00 p.m. What greeted us was a large pool shaded by a very tall cottonwood tree. At its base, a tangle of driftwood, roots, stumps, and smaller flotsam had piled up along most of the exposed roots. A search of this matrix revealed no Palaemnema. We looked again and again and were disappointed time and again. Both of us were tired. We sat and ate beef jerky and drank Coke while we discussed our course of action. "What can be done with one specimen? If it is new, do I describe it?" We didn't know what to think, and we were beginning to wonder is its occurrence there was due to storm winds from Mexico. We were resigned, but decided to trek on up the creek. Directly ahead was the spire of Wildcat Peak, and at its base were Arizona's characteristic saguaro cacti. The whole scene was beautiful, but it still did not assuage our disappointment.

At about 2:30, Jon reached the base of a small cottonwood tree beside a small portion of the creek. All of a sudden, he yelled, "I got one! You see, I am not crazy!" I hurried over and, sure enough, he held a freshly-caught male. It had appeared in a small, triangular orifice in the tangle of cottonwood roots and flotsam. "This is where you got it? Where exactly did you see it?" I exclaimed. I couldn't believe it. Well, where there is one, there have to be others. Our pace quickened, and excitement resurged. But checking cottonwood after cottonwood revealed no more specimens.

Finally, I came to a very large cottonwood tree shading a magnificent, deep pool. The same kind of tangled root matrix lay there as in other places. I saw nothing there, either, but then I noticed that there was a dark opening about the size of my body. I bent down and stuck the handle of my net inside and moved it. I couldn't see much of anything, because it was dark, but in a way I felt a little like Howard Carter, who stuck the candle for the first time into King Tutankhamun's chamber. I thought I saw something move. I had to take off my hat, backpack, and camera pack to squeeze into the chamber. Dirt and debris fell into my hair and down the back of my shirt. But there in front of me a scant two feet away, was the most beautiful sight of the whole day. There was a single male Palaemnema perched on a slight overhanging root. I just couldn't believe it. Slowly I pulled back out, hurriedly opened my camera, mounted the lens, and carefully maneuvered into the chamber again. I snapped off one shot for posterity. I could get no closer, because no maneuvering was possible. No net was possible in there, so I slowly stretched out my hand and picked the damselfly up by its wings. I backed out and went around the other side, where there was another smaller entrance into the same chamber. I was rewarded with another male, which, this time, sat partially exposed to the sun. Its placement allowed me to approach much more closely, and I clicked many more photographs, hoping that one would come out. I picked it up in the same way.

As I sat on the roots of the tree, it suddenly dawned on me: Jon had collected these damselflies when it was drizzling. I thought then that these shy creatures ventured into the atmosphere under such conditions. At other times, such as that Saturday, they remain secluded like troglodytes in the more humid and sheltered microhabitats at the bases of these huge cottonwood trees. These are such ephemeral habitats, prone to violent disturbances in some years of heavy rainfall and resulting floods. I have collected Odonata over much of the globe for the past 35 years. My experience in the tropics has led me to look in places where secretive species may occur. But there is no way that I would ever have looked in such a habitat in the Sonoran Desert. Jon's discovery was truly a serendipitous one. Without his alertness and curiosity, this unique riddle of the Sonoran Desert Palaemnema would still be hidden from us.

We succeeded in collecting, over the two days, seven males and three females. At the end of the second day, my feet were sore and blistered from approximately 10 miles of walking.

When I returned home, e-mail from Nick Donnelly was waiting, and we both decided that this species could be Palaemnema domina. When I sent Nick a male, he noticed some minor differences in overall body coloration and a few small structural differences. Despite these differences, Nick and I are inclined to call this taxon P. domina. The closest known populations are in Oaxaca and Chiapas, Mexico. Nick states that P. domina inhabits the most arid parts of the tropics, compared with the other members of the genus.

So the United States can now claim a new species, genus, and family to its fauna. We will continue to study the specimens and will report on further knowledge later. I thank the officials at the University of Arizona and The Nature Conservancy for their cooperation in allowing us to discover this mysterious damselfly. I especially thank Jon Hoekstra for his unflagging efforts, his enthusiasm, and his hospitality, all of which shows that you can truly make new and exciting discoveries in your own "back yard," if you look hard enough.

[NOTE: The discovery of this interesting damselfly has been published: Hoekstra, Jon D. & Rosser Garrison. 1999. Range extension of Palaemnema domina Calvert (Odonata: Platystictidae) to southeastern Arizona, U.S.A.: a new odonate family for the United States. Proc. Entomol. Soc. Wash. 101(4): 756-759]