Bugs suck - In a good way!
Last time, I talked about the how aquatic insects find refuge during high flows in the hyporheic zone, that region below the substrate. But aquatic insects have other strategies to survive in flowing water, especially fast flowing water. Imagine for a minute what it might be like for a little aquatic nymph living in a fast riffle or run. I think it would be like living in a constant sand storm. To hang on in these conditions aquatic insects have come up with some ingenious approaches. Here’s a look at a few of them.
#1 - Let the gills do the gripping
A lot of mayfly nymphs live in fast water, particularly the clinger nymphs of the family Heptageniidae. A few species in this family have come up with a unique use for their gills besides just breathing. For these species the gills overlap and form a continuous surface creating a suction cup like grip on the rocks they call home. A clever approach that becomes obvious the first time you try to remove one of these nymphs from a rock.
#2 - Velcro anyone?
Here’s another very cool idea developed by a mayfly. In this case it is the species Drunella doddsi, one of the species of Western green drakes. These large nymphs live in fast water preferring large rocks and boulders that rarely get tossed downstream during high water. To hang on Drunella doddsi invented velcro, or at least a good imitation of it. The underside of their abdomen is covered with a pile of ultra fine hairs. The hairs essentially lock into the slightly pitted surface of their rocky home much like two pieces of velcro coming together. Good idea!
#3 - How about a little silk?
Spiders aren’t the only group of Arthropods to come up with silk. The silk worm, a moth larva, is ample proof of that. In fact there are hundreds of species of insects that produce silk like spiders. Some of the most prolific silk producers are in the order Trichoptera or caddisflies. Caddis larvae are best known for constructing beautiful shelters or cases out of all types of streambed materials like sand, small gravel, little snail shells, pieces of leaves, twigs, pine needles, parts of aquatic plants, and various combinations there of. The glue that holds these materials together in such perfectly shaped little houses is silk. But besides using silk to hold their cases together many species also use silk to attach themselves to the stream bottom. Species of the genus Brachycentrus, a group commonly called the Mother’s day caddis by fly fishers, are a perfect example. Brachycentrus larvae feed by attaching themselves to the tops of rocks in fast riffles and then sticking their legs up in the current. Hairs on their legs help them catch small food items drifting downstream.
#4 - Give me suckers or give me death!
The last example I’m going to mention is also my favorite. Here’s an example where “suck” is the best word to describe the approach. The critter in question belongs to a strange family of Diptera called Blephariceridae, or commonly called the net-winged midges. The larvae love fast water sections of streams where they live on the tops and sides of large rocks in the full force of the current. Their answer to holding on is a series of disc shaped suckers that line the underside of their abdomen. Overall they look rather other-worldly, and I think worthy of a spot in the next Avatar sequel. While rarely abundant and of no real importance to catching fish, these guys are widespread in cold streams that trout and trout fishers call home. So keep an eye out for them the next time you are picking up rocks from a riffle looking for mayflies or caddis.
