Tuesday, July 10, 2012

Exotic dancers

The Grand River in Lake County, Ohio, as seen from Lake County Metropark's Hidden Valley Park. The Grand is a state and national treasure, and its status as an official State Scenic and Wild River is fitting. Among Ohio Ohio biologists, the Grand is fabled for its diversity of aquatic life. The stream is tops or nearly so when it comes to Lake Erie tributaries that are largely unspoiled.

Photo: Marcia Rubin

Your narrator (left) and John Pogacnik photograph a freshwater sponge, Spongilla lacustris, in shallow waters of the Grand River. John is a biologist for Lake Metroparks, and one of the finest field naturalists that I know. An outing with him is always sure to produce a bonanza of interesting finds, and I was long overdue for a Pogacnik expedition. His and others discovery of the odd freshwater sponges, as reported HERE, spurred me to arrange yesterday's Grand River exploration. We were also joined by photographer Marcia Rubin; check some of her work out HERE.

I have never been much for jazzy LL Bean-style field clothes, especially on aquatic forays. Such wear is expensive, and I'd just destroy it in fairly short order. If the weather is warm and the water nice, I prefer shorts, an old shirt, and sandals for my creek wading. And wade we did, probably covering two miles or more of river bottom sloshing.

Photo: Marcia Rubin

Of course, one can pay a price for the comfort of sandals. We had just exited the stream after our last trek, and popped into a streamside store at the campground whose owners had kindly allowed us access to their property. I was talking to the lady behind the counter, when I looked down and noticed my feet were bleeding rather profusely. We politely excused ourselves, and went outside to make photos of the leeches that were busily wolfing down my hard-earned blood before I dealt with them.

Leeches, which are segmented worms (I don't know which species these are but will look into it, of course), can cause fairly prolific localized bleeding. To encourage unfettered blood flow, the animal releases a powerful anticoagulant. Their bites are not painful, and it takes a big one 15 minutes or so to become fully sated, at which point it detaches and drops off. If you're in the water the entire time, you may well never know what bit you, until you see the bloody wound later.

A gorgeous dusky dancer, Argia translata, sports ball-shaped eyes of the deepest blue-purple. Dancers are a type of damselfly in the genus Argia, and there are seven dancer species in Ohio. With one exception, all of the dancers are species of creeks and rivers. It quickly became apparent, as predicted by John, that the Grand River would produce scores of dancers and we ended up devoting much of our time to seeking out exotic dancers and photographing them. We were quite successful, finding all six possible species. The seventh is the seepage dancer, Argia bipunctulata, which is a species of fens and marshy springfed seepages.

This dusky dancer was good enough to use Pogacnik's hand as a perch, which provides scale. All of the dancers are close to this size. This shot shows a field character for identifying Argia; dancers typically hold their wings up and slightly elevated above the abdomen, while other damselflies such as bluets hold their wings lower, so that the abdomen is sandwiched between the wings.

I had to cheat a bit on this one. We did see a number of blue-fronted dancers, Argia apicalis, as shown above, but for whatever reason I never made a photo of one. This picture is of a blue-fronted dancer that I shot  along the Scioto River near my house in central Ohio. Blue-fronts are often very common along rivers, and males are a distinctive robin's egg blue.

A miniature work of art is this male blue-ringed dancer, Argia sedula. Its deep rich turquoise eyes and upper thorax stripes contrast nicely with the paler blue thorax lateral stripes and blue-tipped abdomen. This specimen is perched on a blade of Emory's sedge, Carex emoryi. This riparian sedge forms extensive colonies along the Grand River, and its lush meadows provide an important habitat for damselflies and dragonflies.

Perhaps my favorite damselfly is the violet dancer, Argia fumipennis. One doesn't see many purple insects flying about, and the unusual color makes the adult males really stand out. This is a pair in tandem; the male (right) holding the female by her neck with his cerci, or claspers. While mating, male dancers keep a tight hold on the female lest she be snapped up by some other male. At some point, she will twist her abdomen around and connect with the male just below and aft of his thorax, and the transfer of sperm will be made.

This is the well-named powdered dancer, Argia moesta. Adult males are a distinctive whitish-blue on the thorax and abdomen tip. Powdered dancers were by far the most numerous species of dancer that we saw. Their typical perch is on a rock in the river, but animals in such a setting often don't look very good in photos. I waited until one obliging lit on some sedges; the green vegetation makes the dancer really pop.

The powdered dancers were at the peak of mating activities, and their communal ovipositing was a spectacular sight. Females have a bladelike ovipositor which they use to insert their eggs into saturated wood or other plants. There are about a dozen pairs on the branch above, which is floating in the river. The males keep a firm grip on the female as she sticks her eggs into the wood, and they project upwards like little puppets.

We noticed that floating leaves were especially coveted by the powdered dancers, and this sugar maple leaf is completely covered with ovipositing females and their attendant males. These insects are not social; it is the shared need for suitable ovipositing substrates that bring them together like this. It is an uneasy truce, and the males are constantly bumping each other and otherwise squabbling.

John's theory is that powdered dancers seek objects that can float for extended periods to lay their eggs on, as this is a very efficient way to migrate to new locales and thus expand their range. This maple leaf, which was moving downstream with the current, might end up a mile or so downstream before it lodges against something and the dancers' eggs hatch. Such a tactic is an incredibly effective way of ensuring that the species rapidly colonizes an entire stream corridor. The powdered dancers seem to be the most advanced of the damselflies in regards to "rafting migration".

All of these dancers were but a small part of the assemblage of animals and plants that we found, and I'll try and share some of the other finds later.


1 comment:

Bob (in Powell) Burgett said...

Thank you! I thoroughly enjoyed reading this post and LOVE the dancer photos. I learned some stuff, too. The foot/leech photo? Interesting, but maybe not quite as pretty as the damselfly shots... :-)