Every visit to a natural lake or pond feature is incomplete without chancing upon a few aquatic midges. These tiny creatures are fairly omnipresent in those areas, floating in the water as larvae or resting, in their adult forms, in the shadows of fallen logs and leaf litter. No one can be blamed for swatting these insects or running away from swarms as they look just like stinging mosquitoes (Culicidae) to the naked eye!
Fortunately, the resemblance between Chironomidae and Culicidae insects is strictly superficial. Also called lake flies, blind mosquitoes, or non-biting midges, chironomids have no interest in human blood. There are a few anatomical differences that may be seen through a magnifying glass. Aquatic midges lack the elongated mouthparts and the characteristic wing scales that distinguish their lookalikes.
Often used as indicators of ecological shifts, these insects are considered the most abundant type of macroinvertebrate found in freshwater systems. Aquatic midges have a widespread and cosmopolitan distribution. With species numbering in the thousands, many are found as far as the Arctic and Antarctic regions. Some have even adapted to life in marine environments.
Due to their small size and subtle variation, ecologists have resorted to studying genera or subfamilies as a whole instead of individual species. These insects significantly enrich the biodiversity profiles of almost all semi-aquatic, aquatic, and moist soil habitats.
What Do Aquatic Midges Look Like?
Adult aquatic midges widely vary in size, with some being just 1 mm long and others growing to more than 2 cm. Many common species bear an uncanny resemblance to stinging mosquitoes but lack their distinguishing mouthparts. These insects do not bite or attack humans, though they may cluster in dense swarms. Most species have scaleless wings, whereas a few (e.g. Belgica antarctica) are wingless.
Their adult fly forms are generally brown or black in color and have 3 pairs of slender legs. Two pairs are oriented at an outward angle while the third pair, which may be likened to arms or forelegs, is oriented toward the anterior and is usually held together while the body rests on the hind legs. When present, the wings of these flies are scaleless, narrow, and very thin. The presence of plumose or featherlike antennae usually distinguishes males from female chironomids.
Chances are you’ll have come across aquatic midge larvae at least once in your life. If you’ve ever had a bucket of stagnant water spontaneously become occupied by tiny, red wrigglers, you’ll understand why these are commonly called bloodworms. The red coloration is caused by the presence of a substance that is similar to hemoglobin in their hemolymph. Segmented and cylindrical, the larvae have 2 pairs of unjointed prolegs (leg precursors); one is usually located on the prothoracic or first segment behind the head, whereas the other is located on the last abdominal segment.
These pairs of legs serve as important features for accurately identifying chironomid larvae. They aren’t always pink or red-colored, as those of some species are brown, green, or white. Their head capsules tend to be sclerotized, which means they are hard and cannot be retracted.
Aquatic Midge Habitats – Where Do They Live?
Chironomids are so diverse and widespread that they are able to inhabit practically all types of freshwater and brackish water systems. Some have even evolved to withstand marine and terrestrial conditions. In natural bodies of water, their larvae may be found throughout the water column and on benthic substrates. Depth preferences are largely dependent on species and are associated with specific environmental conditions. For example, blood midges are more likely to withstand low-oxygen, heavily-polluted water due to their oxygen-rich hemoglobin.
Lakes, ponds, streams, rivers, springs, and estuaries are all common habitats. Even temporary streams and standing buckets of water can eventually become colonized by the larvae. Once they have metamorphosed into adults, the flies can take wing and navigate to other potential habitats in an effort to feed or mate. They are often found in wetland habitats, riparian forests, or corridors in between water basins. It must be noted that these flies prefer neutral water pH levels and become replaced by other insect families when the pH drops to below 6 or goes above 7.5.
Adults can breed quite effectively in isolated pockets of water as well. They may be found in the damp holes of trees, around small puddles in soil, in rain gardens and ornamental ponds, in pitcher plants, and even on mounds of dung. They can occur as swarms along highways in humid areas. They may be considered pests in these areas as their crushed bodies can accumulate on car windshields. Their droppings can also damage and stain industrial surfaces. Some of the densest and warmest cities in the world are hotspots for these flies.
What Do Aquatic Midges Eat?
Both larvae and adult forms of chironomids feed. Outdated sources may indicate that adult flies don’t consume food, but more recent studies have shown that they are able to metabolize a variety of organic food types. Some species may also function as pollinators as they consume sugar-rich substances, such as nectar, honey, pollen, and honeydew.
The importance of food consumption by adult aquatic midges is often debated, as they don’t necessarily need to feed to survive for long enough to mate. Nonetheless, feeding has been shown to contribute to a longer lifespan in female flies. Also, males can supposedly fly over longer distances if they are sustained by sugar-rich food types.
Their aquatic larvae are able to consume many types of particulate organic matter throughout the food column. Those that reside on the benthos function as detritivores that aid in the rapid decomposition of sunken plant material. Some species specialize in feeding on algae, whereas others are fungivores that favor the fungal spores and hyphae that grow on submerged surfaces. Some are specialized herbivores that can burrow into plant tissues and create tunnels as they mine for their food.
The Life Cycle of Aquatic Midges
Aquatic midges retain the life cycle trends that are common to insects of order Diptera. They are holometabolous, which means their juvenile forms must undergo metamorphosis to reach sexual maturity. Eggs typically occur as gelatin-like masses that are laid onto the water’s surface or on overhanging and emergent plants. They can also be found underwater as they may become detached from vegetation or gradually sink.
Larvae that hatch from these egg masses are very tiny and maintain a planktonic habit. They remain suspended in the water column, feeding on particulate matter. They molt to increase in size and graduate into their subsequent instars. As early as the second instar, the larvae usually sink to the benthic layer and remain there until they have stored enough nutrients to pupate.
After the fourth instar, the larvae begin to develop a protective outer shell and remain in a submerged, sheltered area. During their pupal stage, the developing fly enters a brief period of inactivity. Once they are fully developed, they exit dormancy by breaking out of the pupal cocoon. The adult fly then rises to the water’s surface and flies off in search of a mate.
Adults tend to be incredibly short-lived, but this fleeting period of maturity is common among Dipterans. In a period of about two weeks, they must be able to find suitable mates and lay their eggs. They gather close to potential sites for oviposition. They have the tendency to form swarms while mating, so it should be relatively easy to spot adults in the wild. After putting in the effort to reproduce, the adults begin to die off and can accumulate in pungent piles.
How to Attract Aquatic Midges to Ponds
As chironomids are so widely distributed and their adult forms can travel between bodies of water, they are incredibly easy to attract. If you have an outdoor pond or water feature, there is a very high chance that you already have a resident population. The more naturalized these features are, the more likely it is that adult midges can feed and lay their eggs successfully.
Open surfaces of fully inhabited ponds may not be the safest area for midge eggs or for skating adults, but marginal vegetation should help keep them protected. A structurally diverse pond can help sustain generations and allow for seasonal reproduction. These flies are most likely to travel over considerable distances during rainy periods, as more isolated water features can facilitate their spread.
Are Aquatic Midges Beneficial?
Chironomids play many vital roles in freshwater ecosystems. Their population rates are often indicative of ecological change, so they are often used as biological indicators. Their egg, larval, and pupal stages are fantastic sources of nutrients for predators.
Most secondary consumers will, at one point in their lives, likely develop a preference for one of the chironomid life stages. Surface feeders and filter-feeding organisms would likely feed on the eggs and newly hatched larvae. Benthic feeders, such as fish and crustaceans, are likely to feed on larvae. Insectivorous birds, ducks, bats, and predatory insects can also eat various growth stages.
Apart from their role as food for larger aquatic organisms, midge larvae function as decomposers by feeding on decaying plant material. As they metabolize leaf matter and create tunnels through sunken waste, the larvae help mediate the spread of oxygen molecules and are vital for nutrient cycling. Additionally, adults are ecologically valuable as they are food for terrestrial and semi-aquatic animals. Moreover, their capacity to feed on pollen and nectar can make them desirable pollinators.
Though primarily beneficial, populations that go out of control and generate swathes of swarms can be troublesome and difficult to eliminate. This may occur due to an absence of predators or a seasonal abundance of stagnant water pockets. Maintaining high biodiversity levels in the potential habitats of aquatic midges can help prevent this.
