Springtime is finally here, and with the warmer weather we will soon start to see lots of bugs—icky, stinky, stinging, and biting insects! And you may notice that the swarms of these bugs seem to be denser the closer you get to water, such as the New River. That is because many of these organisms have been living in the water, growing as larva and then pupa over the past year, until they hatch out as winged adults in the spring to live out the remainder of their lives. But as you swat that mosquito, shoe away that black fly, or close your eyes when you walk through a swarm of mayflies, do you ever wonder if these bugs might be telling you something about their environment? 

Once upon a time in the past, miners brought a canary into the mine with them as a way to detect when poisonous gases from the earth might be building up to toxic levels. When the canary died or showed signs of ill health, it was time to get out. In a similar way, certain insects collected directly from the stream can tell you about their surroundings. As the canary is sensitive to low levels of poisonous gas, many species of insects are sensitive to changes in their environment. Some have adaptations that help them resist change, for example midge fly larva (the adults look a lot like mosquitoes, but they don’t bite) have hemoglobin in their blood making it red like ours (coincidently they are sold as fish food in pet stores under the name “blood worms”). When oxygen levels in the water are lowered, often as the result from some forms of pollution, these midge flies are able to survive when other insects cannot. Similar adaptations in other insects include larger gills, smaller size, even the ability to breath air.

There is a whole science surrounding this phenomenon, called biomonitoring. Scientists collect the insects from the river or stream and identify and count what is in the sample. By looking at the community of different bugs, scientists can get an idea as to what may be going on. A healthy stream may include several different species of bugs comprising an entire ecosystem with shredders (large stoneflies) feeding on leafy plant material, scrapers and grazers eating the algae from rocks, filter feeders (some caddisflies and blackflies) collecting fine material from the water current, and of course predators (dragonflies, damselflies, and some beetles) that eat the rest.

Conversely, a potentially impacted stream will likely have fewer of the groups listed above. Also, certain bugs that are able to resist poorer conditions within the stream tend to be more numerous. Things that can negatively impair a stream are classified into two groups. The first group is called non-point, because their sources cannot be easily traced within the landscape surrounding the stream. These may include leaky septic systems, fertilizer runoff from homeowners, even runoff from agriculture (fertilizer or cattle waste). The second group, called point sources come from direct traceable inputs into a stream. These may include storm drains, erosion from poorly managed construction sites, and direct piping of wastewater from many different types of industries.

One way to monitor stream water quality is to collect water samples and submit them to a laboratory for testing. However, unless one knows specifically what to look for this type of testing can be costly. Also considering the natural function of a stream is to move water from one location to another, it is entirely possible to miss something if the water is sampled after a pollutant entered the stream. Consider chemical sampling like taking a photograph—you will see a chemical snapshot of the stream at the time the water samples were taken, and nothing else. Biomonitoring is more like watching a home video. The bugs within the stream at any given time are representative of everything that has happened to that stream up until the time of sampling.

So the next time that pesky insect is bothering you, consider its origins. While not all the bugs around you come from the nearby stream, many do. And those from the water can tell a great deal about the streams, rivers, ponds and lakes in your backyard, if you know how to listen. To find out more about your local water bugs talk to a fly fisherman, do an Internet search (for mayflies, stoneflies, caddisflies, etc.), or volunteer with any of the local citizens groups who routinely monitor local streams (such as Save Our Streams or National Committee for the New River) and you too can learn how to listen to what nature is saying about the water quality in your area.

Gerald Shepard is an aquatic entomologist with Environmental Services & Consulting, LLC in Blacksburg.