This month we’re celebrating one of Minnesota’s most prominent natural resources – our lakes! We love them for swimming, boating, fishing, sunset gazing, and so much more. In order to keep enjoying these things, we need to ensure that our lakes are clean and healthy. But how can we tell? One way to tell is to look at the bugs in the water! One of my favorite classes to teach with Happy Dancing Turtle is our Wacky Water Bugs class – here’s a short summary of what we learn.
Before we can learn how insects can tell us if the water is clean and healthy, we need to understand some basics about insect life cycles and survival strategies. Insects can have two different types of life cycles, but both types play an important role in insect survival during winter. Insects that go through incomplete metamorphosis have three stages (egg, nymph, and adult) while insects that go through complete metamorphosis have four stages (egg, larva, pupa, and adult).
Conjure up a picture of a winter scene in your head. Chances are, insects are lacking from your image of winter. So where do they go? A few, like Monarch Butterflies or Green Darner Dragonflies, actually migrate to warmer locations in the south for winter. But most insects stay here, surviving in various stages of their lifecycle. A few insects survive as adults - honeybees overwinter in their hives and some of the earliest butterflies we see emerge in the spring have spent the winter hibernating under bark or in small crevices. Winter kills all the adults of some insect species, like grasshoppers or walking sticks, which rely on eggs laid in the fall to bring the next generation the following summer. Quite a few insects survive winter by spending it in the pupa stage, giving them a nice, long time to transform into their adult shapes. However, many insects in our area survive winter by spending their nymph or larval stage in the water, beneath the frozen ice covering water in winter. In fact, in North America, there are 8,600 species of insects that rely on freshwater habitats during all or part of their life cycles!
Dragonflies, damselflies, mosquitoes, caddisflies, mayflies, craneflies, alderflies, dobsonflies, stoneflies, and snipeflies all spend their early life stages in the water before emerging as adults. Finding them during their aquatic life stage can indicate the health of our freshwater habitats if we know something about their pollution tolerance. Our Wacky Water Bug class focuses on going to rivers, streams, ponds, or lakes to look at macroinvertebrate indicators. Let’s break that term down. “Macro” means large and “invertebrate” refers to an organism without a backbone – so we’re looking for things with no backbones that we can see with our naked eye. Some examples of aquatic macroinvertebrates are insects (dragonflies, damselflies, beetles, etc.), clams, muscles, snails, and crayfish. An “indicator” species refers to a plant or animal whose presence tells us something about the environment. Aquatic macroinvertebrates vary in the degree in which they can tolerate pollution – some are very sensitive while others can tolerate high amounts of pollution. If you collect a sample of aquatic insects from a particular habitat, you can measure the health of the habitat (a process called biomonitoring). If your sample includes many species that are NOT tolerant of pollution, that indicates the water there is fairly clean and there is a healthy habitat. If you find a lot of species that CAN live in polluted water, that doesn’t necessarily mean the water is polluted, because those species can also live in clean water. So pollution intolerant species are more helpful in assessing the quality of our water.
If you’d like to try assessing the quality of a freshwater habitat near you, make sure to bring along a few guides to help you out! We’d recommend the UW Extension’s Key to Macroinvertebrate Life in the River and Key to Life in the Pond, as well as the UW Extension’s Data Collection Sheet. Here is another example of how to determine the health based on the pollution tolerance of species you find.
But it’s not just water bugs that tell us something about our aquatic environments! Other types of animals can be indicator species as well, you just have to know a little bit about the habitats they like to live in! Here are a few other indicator species to watch out for:
Common Loons - these birds can dive up to 200 feet to find their food in the water! They find it using their eyesight, so the water has to be relatively clear for them to see, and they need a healthy fish population to keep them well fed! Loons also prefer to nest on shorelines with tall, native vegetation, which also helps keep our lakes clean by filtering run-off before it enters our lakes.
Tullibee - this small fish lives in deep lakes and needs highly oxygenated water to survive. Eutrophication (excessive plant growth in lakes that depletes oxygen supplies, often due to nutrient-rich runoff entering the water) causes Tullibee populations to decrease. Lakes with a lot of Tullibee indicate good oxygenation and possibly healthy game fish populations (like walleye, muskies, and northern pike), as many of our game fish feed on Tullibee.
Brook Trout - one of Minnesota’s two native species of trout, this fish can only survive in very clean and cold water, relying on their vision to feed. When water becomes acidic due to pollution (i.e. from mine drainage or acid rain from coal power plant emissions), turbid due to erosion or runoff, eutrophic due to runoff, or warm due to deforestation (loss of shade) along the riverbank, the trout species are typically the first to decline.
Amphibians - frogs and other amphibians start out in the water using gills to breathe. As they grow into their adult forms, they still rely heavily on aquatic resources, absorbing water and sometimes even breathing through their skin! Because their skin can absorb gases and liquids, they are very sensitive to environmental changes. Large population declines in amphibians have been reported globally, as well as some species with an abnormal rate of deformities due to pollution in their habitats.
So next time you’re out enjoying your beloved lake, take a few moments to observe the animals in the surrounding habitat. What can they tell you about the health of the ecosystem you’re in? What can you do to help ensure they have a healthy habitat?