The bug of the week
Have you noticed that each week it seems like there's a different large swarm of bugs by the lake? One week it's dragonflies, one week it's mayflies, one week it's midges, and so on. The swarms are massive, and then a few days later they're all dead on the ground. These are aquatic insects that actually emerge out of the lake. Aquatic insects are insects that live in a lake or stream for some part of their life.
Aquatic insects are very diverse and abundant in lakes, although you usually don't notice them in the water. Don’t worry, the bugs in the water rarely bite or affect humans at all while swimming! In fact, most of them live burrowed into the sediments at the bottom of the lake. Most people only notice the adult forms of aquatic insects flying around by their porch lights at night, crawling on their boats or by lake vegetation during the day. Dragonflies, damselflies, mosquitoes, midges, mayflies and many more insects live in the lake during their immature life stage (nymphs and larvae) and fly on land in their adult life stage. You can think of the immature life stage and adult life stage as the equivalent of a caterpillar and butterfly. Water beetles such as whirligig beetles and water bugs such as water boatmen, water striders live in the lake all their life.
The reason it seems like there is a different mass swarm of bugs every week and then they die has to do with the aquatic insect lifecycle. The aquatic insects that live in the lake as a larva (caterpillar) often spend a year or more in the water eating and growing. When the adult emerges out of the lake, the large swarms you see are mating swarms. Once the adult mates, it dies a day or two later. Some aquatic insects such as mayflies and midges don't even have mouthparts as adults because they're only adults for a couple days to mate and then they die, so they don't even need to eat.
Aquatic insects play a major role in the lake ecosystem. They help break down and decompose the dead material at the bottom of the lake such as leaves, dead fish, and other organisms. They are also a major food source for fish, frogs, birds and other animals. Without insects in the lake, it wouldn't be a very nice place to fish or swim!
Aquatic insects are good indicators of water quality and habitat quality in lakes because they have a wide range of tolerance to pollution. Some insects can live in any type of water, even green lakes with high algal concentration and a mucky bottom (midges). Other insects can only survive in water that is very clean and clear and has a high concentration of dissolved oxygen (mayflies and stoneflies). Still others are in between (caddisflies, dragonflies). By collecting insects from the lake and identifying them to see which type they are, we can draw conclusions about the water quality of the lake. If there are a wide variety of insects in the lake that can only survive in very clean water, we can conclude that the lake is in good condition. If only a few types of insects are found and they are the ones that can tolerate poor water quality conditions, we can conclude that the lake has poor water quality.
If you would like to see pictures of these aquatic insects and their names, you can visit: http://www.entomology.umn.edu/midge/VSMIVP.htm.
Until next week, enjoy the lakes!
Moriya Rufer is the Lakes Monitoring Program Coordinator for RMB Environmental Laboratories in Detroit Lakes, 218-846-1465, lakes.rmbel@eot.com