June 19, 2008
This show originally aired on August 2, 2007 and then again on June 12, 2008 on “The Rivanna Rambler,” a weekly public affairs show airing every Thursday at 11:55 a.m. on WTJU 91.1 FM or wtju.net
She fairly coos at them, these bugs, these tiny aquatic insects who, in their larval stages, can reveal much about the health of the river. Rose Brown, Program Manager and Volunteer coordinator for StreamWatch, is my companion for the morning at Rivanna Mills down in Fluvanna County. The overflow chute is now a shallow cobble filled channel below the rapid. It is here that we’ve grabbed our sample, set up our table and are culling through a net full of the results.
“I see you,” Rose says to a healthy sized stonefly that’s crawling through the wet debris away from her blue plastic forceps poised to snatch, ever so gently, the bug and place it in a white plastic ice cube tray filled with water and used for counting the specimens. I, too, am talking to them … “Here you go,” and “there you are” — especially the caddisflies and, of these, especially the more exotic casemakers.
And it is hard not to talk to them – for once you have seem the elegant home that the longhorned casemaker crafts of the detritus from the bottom of the river, you are likely to think of these tiny insects as entities worthy of respect, if not conversation, however one-sided it might be. I find individuals of this family of caddisfly in slender tapered cases the length of my fingernail and attached to the dark-green filamentous branches of the pondweed that came up in the sample net along with leaves, bugs, aquatic clams, and a few snails. The larva builds this case from small pieces of plants, fine particles of sand and rock, and the pure silk that it excretes from its mouth parts. This portable case is its protection during the larval stage – and like other caddisflies – its sanctuary during the metamorphosis into the adult hood.
The river is low – and though the last rainfall was three nights ago – it is still cloudy with sediment. Though only a foot to two feet deep in most places, I could barely see the bottom as we paddled down here by canoe. The owner of the farm where we put in reported gobs of algae growing at the small launching beach, and while we saw little of this as we paddled the mile downstream, the water felt thick and we had to navigate around dense mats of common waterweed. Everywhere, bugs were swarming, evidence of recent and prolific hatches.
So perhaps it is no surprise that we have an equally prolific net full of bugs – all told over 500 – and that a good many of them are caddises. And new to me are the micro caddisflies, their cases tiny oblong orbs smaller than a grain of rice, fashioned from sand and detritus. Through a hand lens, I can see the tiny head and forelegs emerge first at one end and then at the other. This casemaker lives its fifth and final larval stage almost entirely within the case and accommodating growth of its body parts by cutting along the bottom seam of the purse-like structure, adding material to both sides, and then gluing the two halves back together again.
While we cull and count, Rose and I share our experiences of learning to love the bugs – for each of us, it took several tries – sessions pouring over the contents of nets, with simple field references in hand to distinguish the aquatic stonefly from the mayfly, the dragonfly from the dobsonfly from the black fly. Persevering, going out with experienced samplers, and above all, taking the time to watch the critters magnified with the hand lens, crawling on my palm in a small puddle of water, is what eventually came to captivate me. The next stage – and one that I suspect will be for life-long learning – is starting to understand the life cycle of these bugs: how they mate and eat, and how they transform into life above the water’s surface, where in swarms they signal to fisherman while they tantalize fish.
Caddisflies are diverse in their habitat preference and eating habits, but most are scrapers of some kind, removing their food from surfaces of rocks and cobble, leaves of plants and strands of algae. Many species are considered facultative, meaning they occur in waters from pristine to moderately disturbed and are often found in abundance when there has been moderate disturbance of some kind. The science of using the relative abundance – or lack thereof – of these bugs to predict water quality is what has been used in upper stretches of the Rivanna in Albemarle County which are now considered biologically impaired – in other words, not meeting standards for supporting a rich and diverse assortment of aquatic life. Counting bugs with StreamWatch is one way to keep tabs on the health waters of the Rivanna.