StreamWatch Bugs: Midges

Non-biting midges, family Chironomidae, order Diptera

Non-biting midges or chironomids are the most diverse and abundant family of aquatic insects in the US with over 1000 species in North America. They often account for as much as 50% of the species found on the bottom of a stream or lake. It is not uncommon to find 5000 midges per square foot on the bottom of a lake. They live in a wide range of habitats – swift streams, slow moving rivers, lakes, stagnant ditches, ponds rich in decomposing organic matter, and even pools of raw petroleum. Different species of midge respond differently to impairment, ranging from very tolerant, to intolerant. If you know how to distinguish midge species, they are probably the only aquatic insect needed to characterize the health of a stream or lake.

BENEFICIAL ASPECTS

Midges are an important food source for fish and predatory aquatic insects. Larvae clean the water by consuming and recycling organic debris.

LIFE CYCLE

There are four stages in the life cycle of chironomid midges. Eggs are laid on the surface of the water. Each egg mass may contain up to 3000 eggs depending on the species. Eggs sink to the bottom and hatch within a week in the summer. After leaving the egg mass, larvae burrow into the mud and consume suspended organic matter in the water and mud. In the summer the larvae pupate after a few weeks, and swim to the surface where adults emerge after several hours. Adults do not feed. In the fall, larvae do not pupate, but suspend development and pass through the winter months as mature larvae.

REPRODUCTION

Adult males form swarms situated over prominent objects on the ground such as a fence post, or a person. Many different species may be in the swarm. When a female flies into the swarm, males of her species mate with her. The males recognize the females of their species by listening. The males have brush-like antennae with many hairs emerging from a central stem. Each hair base has a nerve that is sensitive to the wiggling of the hair which can be caused by sound. Different hairs are sensitive to different frequencies. So these antennae are external ears that are frequency-sensitive, playing the role of the cochlea in the mammal ear. Different species of midge fly with a different frequency of wing beat, making it possible for males to recognize members of their own species. When you are outdoors during a midge bloom, you can hear a high frequency hum caused by their wings. The pitch of the hum is higher in the early summer when the midges are smaller.

ANECDOTES

In urban environments where homes are built near lakes or streams, adult midges can emerge in such numbers as to be a real nuisance. They stick to wet walls of a house or car or a sweaty face.

Midges on a living room window

A recent baseball game (October 5, 2007) between the NY Yankees and Cleveland Indians, played in Cleveland near Lake Erie under lights in the evening was bothered by a dense bloom of midges, attracted by the bright lights. The TV coverage clearly showed many midges in the air and stuck to the face and neck of the infield players. The Yankee pitcher who was on the mound when the bloom appeared was so bothered he started throwing wild pitches. Yankee fans blame their loss of the game (and the series) on the midges. Joe Torre (the Yankee manager who recently lost his job), recently said one of his regrets was not to have asked the umpires to stop the game when the midges appeared.

  • Midges are sold as pet fish food.
  • Their fossils are used as indicators of past climate changes.
  • They are more sensitive to horizontally polarized light than vertically polarized light. (This may be because light reflected from a water surface at a glancing angle is mostly polarized horizontally.)
  • In Minnesota a small stream named Minnehaha flows through suburban Minneapolis into the Mississippi river. The University of Minnesota has observed 134 different species of midges in Minnehaha. When we were there, we did a brief sampling and found mainly black flies.
  • Fly fishermen tie many imitations of midges, among the smallest flies used in fly fishing. Imitations of larvae, pupae, and adults can be found in the catalogs of flies for fishermen.

Below are shown pictures of large late-summer male and female midges.


Male adult midge ~1/2 inch long
Female adult midge ~1/2 inch long

Enlargement of one of the antennae of the above male. This is a remarkable organ for any critter, regardless of size.
Same male midge illuminated from above to show color.

References

  1. Voshell Jr., J. Reese, A Guide to Common Freshwater Invertebrates of North America
  2. Apperson, Charles, Michael Waldvogel and Stephen Bambara, Extension Entomology, NC State University, Biology and Control of Non-biting Aquatic Midges