Deep Water Chironomids Feeding and Swimming

The most productive part of a lake is the littoral zone where the penetration of sunlight allows for the rapid growth of aquatic plants and periphyton. Here is where you will find the highest level of bug biodiversity, including a hundred or so species of chironomid (midge) larvae. But this doesn’t mean that the deep water areas of a lake are devoid of life. In fact, there are some genera of chironomids (Chironomus and Glyptotendipes) that specialize in hiding in the low-oxygen layer of mud during the day, and coming out at night to forage for whatever tiny organic particles of food they can find.

While the diversity of midge larvae living in the mud 15 to over 60 feet down is low, the biomass (number of organisms) can be very high. This is because, with very little oxygen to support life in the hypoxic mud layer, there is little competition for food. The midge species that can live in this layer of mud are able to monopolize on the resources, much like the mono-culture of a wheat field.

One would think that there is not much to eat way down there in the depths, but as organisms living in the upper layers of the limnetic zone die (algae, zooplankton and cyanobacteria), or organic bits get blown onto the lake’s surface (pollen and organic dust), they settle to the bottom. This translates into a continuous shower of food for most of the year, even in the deeper parts of a lake.

This video shows midge larvae foraging for food on the lake bottom and their swimming behavior when they decide to move longer distances to find better foraging sites. Their swimming behavior is unique, and somewhat frantic, and not easily imitated by the fly angler.