Have you ever wondered where dragonflies and other insects go during the winter?
Most people consider dragonflies and damselflies to be terrestrial flying insects, but in fact, they spend more than half of their lives in the water. During the summer and early fall, adult Odonatans lay eggs in wetlands, lakes and streams. Once they hatch, the nymphs (which look nothing like adults) continue to live in the water for anywhere from two months to five years.
There are 140 species of Odonata in Minnesota. A handful, such as the common green darner, migrate over the winter; the rest overwinter here in their larval forms. The ebony jewelwing – a delicate damselfly with a turquois body and jet-black wings that is found along rivers and streams – only lives for two weeks in its adult form. It is a short, but brilliant life.
Odonata are not the only insects that spend a portion of their life underwater. Mosquitoes, caddisflies, mayflies, stoneflies, and many others do as well. In fact, one of the best measures of stream health is the amount and biodiversity of macroinvertebrates we can find in the water. The prefix “macro” means we can see them with our eyes – we don’t need a microscope, and “invertebrate” means they don’t have a backbone. Along with insects, other common freshwater macroinvertebrates include leeches, mollusks (mussels, clams and snails), crustaceans (fairy shrimp and water fleas), and water worms. Collectively, these little critters are foundational to a healthy aquatic food web needed to support turtles, trout, and other wildlife.
In the Stillwater area, Brown’s Creek provides a real life illustration of the importance of aquatic insects and other macroinvertebrates. Brown’s Creek, a designated trout stream, has been listed as impaired since 2002 for a “lack of cold water assemblage”. This fancy phrase basically means that conditions in the stream were no longer favorable for macroinvertebrates or the trout that eat them to survive. The water is sometimes too warm due to stormwater runoff, and for a while, there was too much copper in the water as well. Over the past 15 years, Brown’s Creek Watershed District has done a lot of work to improve the creek, and biologists are now finding more macro invertebrates in the water and more trout surviving in the creek as well.
You may be surprised to learn that high school students actually help to conduct much of the macroinvertebrate sampling on Brown’s Creek and Valley Creek through a volunteer stream monitoring program. Aaron DeRusha, the program lead at Washington Conservation District, instructs students on how to properly collect samples and identify the critters that they find in the streams. Despite a challenging year, DeRusha worked with 50 students in 2020 over the course of several limited in-person and remote sampling events.
Across the state, the Minnesota Pollution Control Agency has found that stream health varies dramatically. In the north-northeastern and Arrowhead regions, roughly 74% of rivers and streams are meeting water quality standards for aquatic life; in southern and western Minnesota, only 16% of rivers and streams are in good health. In the central region and Twin Cities metro, the best quality streams are located in less developed areas. Currently, 37% meet water quality standards, and most of those are small streams, such as the tiny tributaries that flow through woods to the St. Croix River in eastern Washington County.
The recipe for a healthy stream includes many components – protection from urban and agricultural runoff pollution; an intact buffer of bushes, trees and native plants along the water’s edge; and physical features including riffles, runs and natural bends. When the ingredients come together perfectly, we find water full of life with turtles, fish, and lots and lots of bugs.