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MIDGE LARVAE

SCIENTIFIC NAME: Chironomiidae

NUMBER OF SPECIES/DISTRIBUTION 
There are over 20,000 different midge species worldwide.
  • They can be found throughout the world on all the major landmasses, including the Arctic and Antarctic, and are even found on most islands.
DIET/FEEDING
Feeding habits vary greatly among the many thousands of midge species. They can be collectors, scrapers, shedders or predators.
  • Feeding methods and strategies of midge larvae can vary greatly depending on the size of the larvae, their stage of development, the quality of food available, the composition of sediment, and seasonal/environmental variations.

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Midge Larvae

  • Some species have larvae that are called 'collectors'; these feed on organic particles deposited along the substrate.
  • Others are called 'filter feeders', and they consume tiny particles of detritus and diatoms that are suspended in the water. They do this by using silk nets secreted from special glands.
  • There are also some types of larvae that have highly specialized feeding appendages (called 'mandibles') that they use to scrape bacteria, algae, and diatoms from various surfaces; these species are called 'scrapers'.
  • 'Shredders' is the term used to describe species that chew and bore into living plants, submerged wood, leaf litter, and macro-algae.
  • Some species can also be predatory, feeding on other midge species, aquatic earthworms, roundworms, and other small invertebrates.
  • As adults, midges often do not feed. Those that do usually feed on plant nectar.
HABITAT
Midge larvae are able to thrive in a wide range of habitats, from pristine to polluted, fast-flowing to stagnant, and fresh water to marine.
  • Larvae can be found in benthic regions among the debris and aquatic vegetation. They also dwell in soft sediment and on the surface of rocks.
  • Many species are 'burrowers'. They burrow into the bottom substrate and build small tubes or cases out of silk below the surface of the substrate.
  • Some species of midges are known as 'blood midges'. They contain the red blood pigment 'hemoglobin', which allows them to absorb oxygen from the water more readily. As a result, they can survive in habitats with very low levels of oxygen, including heavily polluted areas.
  • The midge pupa stage may be found near the surface of the water or attached to submerged substrates and in benthic debris.
  • As adults, midges tend to stay close to the larval habitat.

LIFE CYCLE
Midges undergo 'complete metamorphosis', meaning that they pass through 4 complete life stages. These are the egg, larvae pupa and adult stages.

Eggs
  • Adult female midges lay their eggs in aquatic habitats. They may scatter them over the surface of the water, or deposit them in a gelatinous mass on emergent vegetation. Some species may lay eggs in or under the water's surface.
  • Eggs usually hatch in anywhere from a few days to one month. This can depend on the species and on environmental conditions; the eggs may stay dormant for long periods of time.
  • The females generally produce one batch of eggs.
Larvae
  • Midge larvae develop through four stages before transforming into adults. The stages are known as 'instars', and can last anywhere from 2 weeks to 4 years.
  • The first instar is usually planktonic, floating in the water column. Later instars descend to the bottom and are usually benthic.
Pupal
  • When the fourth instar reaches the end of development, the thoracic segment of the larvae begins to swell as the pupa layer forms. The pupa often stays sheltered in debris or attached to the substrate or produces a cocoon as it transforms into an adult.
  • Upon completion of development to an adult, the pupa swims to the surface of the water and the adult pulls itself out of its protective pupal layer.
  • The pupa stage is short, and lasts only from a few hours or days to 1-2 weeks.
Adults
  • In most species, adults emerge from the pupa stage simultaneously, producing large mating clouds with huge numbers of mainly adult males trying to attract females.
  • These swarms last no more than a month, and may last only 1-2 weeks. In most species, adults live only for a few days; in some species they may survive for a few weeks.
  • Adult midges generally do not feed, but may drink water or nectar.
  • Most midge species have only 1 or 2 life cycles per year, but some may have up to four generations per year. In colder regions, it may take over a year to complete a life cycle, whereas tropical species may complete a life cycle in just a few weeks.
  • Species with only one generation per year usually emerge in early spring, late autumn, and winter. Species with two generations per year emerge as adults in spring and summer to early autumn.

 

 

 

ROLE IN FOOD CHAIN
Midge larvae play an essential part in many freshwater ecosystems. They often comprise a huge proportion of the primary consumers in these systems.

  • Midges are so widespread and occur in such large numbers that most predators will feed on them at some stage of development.
  • Midge larvae harvest a large amount of energy from the detritus that they consume; they help to cycle this energy back into the food chain.
  • These larvae aid in the decomposition process and the recycling of nutrients.
  • Some of the organisms that feed on them include insects, fish, birds, and other aquatic invertebrates.
INTERESTING FACTS
  • Adult midges are often confused with mosquitoes. They can be distinguished from mosquitoes because, unlike mosquitoes, they do not bite and lack scales on their wings.
  • In colder regions, the midge larvae may over-winter in the pupa stage within the sediment.
  • The larvae tend to be most active at night in the dark, which provides some protection from predators.
  • Midge larvae can range anywhere from 2 mm to 30 mm in length.

Sources
California State University (2001). Ceratopogonidae. Available here.
DMI International Corporation (2003). LaMotte Aquatic Macroinvertebrate Insect Identification Flashcards.
Murray Darling Freshwater Research Centre (2006). Chironomidae. Available here.
University of Michigan Museum of Zoology (2009). Chrionomidae. Available here.
University of Minnesota; Guide to Aquatic Invertebrates of the Upper Midwest (2004). Diptera. Available here.

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