Aquatic insects keep waterways active

Lake residents are happy to have the FBI on the job at area lakes — but not the famous Federal Bureau of Investigation.

The FBI that is welcomed is the Fungi, Bacteria and Insects that are important in the lake ecosystem.

The FBI are the tiny critters that decompose all of the organic waste that falls to the lake bottom. They break down dead plants and animals into simple substances that are recycled into the food web. Without decomposers, the lake would be overwhelmed by dead bodies and waste. Thanks for your service, FBI.

This article is about the “I” in FBI, the aquatic insects, which ecologists call benthic macroinvertebrates. Most aquatic insects have a life cycle that includes egg, larvae, pupae, and adult. The eggs, larvae and pupae are typically aquatic. These aquatic stages have two great benefits to humans, ecological and informational. First, they are at the base of the food web, collecting and eating all of the material processed by the fungi and bacteria, and then carrying that recycled energy up the food web to fish and fowl.

Second, the aquatic phase of the bugs can serve as biological monitors that send messages about water quality. Some species tolerate poor water quality, some don’t; biologists can read the messages in the kinds and numbers present in the benthic invertebrate community. The critters often tell a more complete environmental story than chemical analysis alone.

For example, in the northeast corner of Brookings County is 400-acre Oak Lake, home of SDSU’s Oak Lake Field Station. The land and water of the Field Station get studied a lot! The aquatic insect community in Oak Lake is typical of our glacial lakes – there are hundreds of species living on the rocks and aquatic vegetation. When sediment was added to test sites, the insect community changed to types more tolerant of sedimentation, thus showing that the bugs had a story to tell. (SD Academy of Science 87:45).

The adult insect is the life phase is more familiar to lakeside residents. The adults of some species remain aquatic, like the whirligig beetles that swim in swarms on the surface, or the water boatman (called water fleas) that dart among the rocks and plants underwater. I wrote about water boatmen this spring in Lake Campbell.

“I saw them as I waded along the shoreline casting for dinner on March 25, a calm, clear day. The water was crystal clear. As I waded, I noticed a few half-inch long “water fleas” flitting amongst the stones. With my eye trained to water fleas, I began to see more and more, even swarms and clouds moving in the water column. I captured a few. Under my microscope, these critters were an amazing sight – bug body with big eyes, hairy surface, and those paddle-shaped front legs! They were water boatman – a good name because they move by rowing with those oar-like legs. They live through the winter as adults under the ice - I bet the spring migrating ducks know about them too.”

However, it is the winged adults that emerge from the water, and get our attention because they interact with humans is good ways and annoying ways. A good bug is the dragon fly.

We notice the rapid flight of the charismatic dragon fly, which is known as a mosquito hawk. Dragon flies are voracious predators that eat mosquitoes and other flying insects.

The dragon fly nymph is also a predator, using an amazing hinged lower lip that is extended to capture prey, even small minnows.

I classify the annoying insects into two categories – slightly annoying and very annoying. Both types were recently found in a survey at Lake Campbell. The sample was collected using a small basket of rocks that was placed on the bottom for several days, which is a standard sampling method that even quantifies surface area. When the basket was retrieved, the insects that colonized the rocks were counted and identified. The Lake Campbell sample had at least 22 species. Most common were flies (family Diptera), midges (Chironomids) and worms (Oligochaetes). When characterized by feeding guild, about 60% were shredders or gatherers that were doing their decomposition duties, and 40% were predators.

In the sample was an example of a slightly annoying species – the midge or lake fly. Lake flies don’t bite, or eat, they just breed, laying masses of eggs on the water surface. After going through their aquatic phases, the winged adults emerge from the water and swarm around lights at night, sometimes covering porch posts and sides of lake cabins. These inch-long, delicate flies have big feathery antennae that distinguish them from mosquitos. The aquatic stage is fish food; the winged adults are bird and bat food.

Also in the sample were one-quarter-inch-long white worms, the aquatic stage of a super annoying species, a member of the fly family with the tongue twisting scientific family name Ceratopogonidae, which in layman’s language means “no-seeums.” These biting flies are small but yikes, do they bite.

No see-ums want your blood for egg laying The burning itch seems to last and last. I have to be generous when thinking of an ecological value for this species.

Mosquitoes are also in the very annoying category, but none were found in the samples or Oak Lake or Lake Campbell. Lakeside residents still get mosquito-bit, because the bug’s favorite habitat is stagnat water, and there is plenty of that around in ditches. The mosquito life cycle is included in every beginning biology book as the example of the insect life cycle with an aquatic and terrestrial phase. There are about three dozen species of mosquitoes in South Dakota. Most are just annoying, but some species transmit the West Nile Virus that can cause illness in about 20% of people who are bitten.

Aquatic insects are so important to understanding lake ecology that the Lake Campbell Sportsmen’s Club will be learning more about this subject at their Monday, August 3 (7 p.m.) meeting. Lake Campbell residents frequently call for some sort of mosquito control — where are all those mosquito hawks when you need them!

Guest speakers are Ms. Deb Springman, a biologist with the Big Sioux River Water Development district, and Dr. Mike Hildreth, Professor Emeritus at SDSU. The speakers will focus on the adult bugs that we see and encounter.

The meeting is also the Club’s annual Ice Cream Social.

Attendance is free and open to the public.

For more information contact Club President Chuck Berry, 690-1252.