What is a benthic macroinvertebrate, you ask? The word “benthic” means “of, relating to, or occurring at the bottom of a body of water” (the lowest level of a body of water is known as the “benthic zone”). Micro is a well-known term, meaning tiny or extremely small. Macro is the opposite, meaning large in scale or scope. It’s something we can see with our naked eye, without the help of something like a microscope. And finally, invertebrates are any creatures without a backbone. So, benthic macroinvertebrates are species that live at the bottom of a creek or stream which have no backbone and are large enough that we can see them with the naked eye.
The next question you might ask is, why are they so important? Benthic macroinvertebrates are important indicators of the health of a steam and the quality of its water. This is due in part to the fact that some species can live in degraded, polluted waters, while others cannot. When we collect these diverse bugs, we are looking for and hoping to find those species that can only survive in clean, unpolluted waters. If there are many of them, and a diversity of types, it’s a good sign that the water is likely to be healthy. On the other hand, if we are not finding those intolerant species and only collect bugs that are very tolerant of pollution, it may be an indication of something deteriorating the quality and health of the water and the habitat it provides.
These species are also excellent indicators of that habitat’s health because they spend most or all of their lives in one place and cannot easily escape pollution, unlike fish, for example, who can swim away. Over time, generations of these creatures provide a long-term view of the stream, unlike the momentary snapshot of a one-time chemical test of the water. As we observe how the bug populations change with time, including population density and diversity, we can discover how the stream as a whole is changing.
Along with our volunteers, we find spots in the creek where there’s a riffle, a shallow section of the stream where the water is flowing rapidly over the rocks, gravel, sand, etc. Downstream of the riffle, one person holds a kick net with one end wide open to catch as much as possible in the net as water flows in. The other particpants then stand in the riffle and kick up as much of the stream bottom as they can. This disturbance of the creek bottom causes all of those tiny creatures living on and under the rocks, sticks, leaves, etc. to get caught up in the current and flow right into our waiting net.
We do this three times, in three different spots, preferably three areas with some variety to them, perhaps in the velocity of the water or the type of material on the creek bottom. After each kicking, the sample is gathered into a bucket so that it can be combined. A portion of that then goes into a mason jar and preserved in alcohol until we can pick through the sample at a later date. The entire process is fun and fascinating and a great way for volunteers to get an even better idea of their stream’s health. They can see for themselves just how much life is actually in their stream and how diverse that life is (or isn’t). These bugs tell us a lot and become an essential and important part of the high-quality data Blue Thumb provides to Oklahoma and the Environmental Protection Agency.
Collecting benthic macroinvertebrates to study water quality has been around for many years and is practiced around the world. The Environmental Protection Agency provides some great information on water quality monitoring - https://www.epa.gov/national-aquatic-resource-surveys/indicators-used-national-aquatic-resource-surveys
Benthic macroinvertebrates are also an important part of freshwater ecosystems and the food chain. Read more about the roles they play in this article from BioScience: