Crane Fly Larvae

Scientific Name: Tipulidae

Number of Species/distribution
There are over 14,000 species of crane flies throughout the world.
  • This makes them the largest family of all the fly species.
Diet/Feeding
Crane fly larvae have a variety of feeding techniques, which is because they obtain nutrition from a range of different sources.
  • Some species are referred to as 'shredders' because they use well-developed specialized feeding appendages (called mandibles) to shred and feed on algae, bacteria, and diatoms from the surface of rocks, sediments, wood, and other submerged objects.

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Crane Fly

  • Other species are referred to as 'predators', using their mandibles to kill and consume other living aquatic insects and invertebrates.
  • Still other species are categorized as 'collector/gatherers', and they feed on decomposing organic material, such as bacteria and feces, which have been deposited by animals or water currents.
  • Some species tend to feed on roots and other vegetation, and may cause damage when in large numbers.
  • As adults, crane flies usually do not eat but may feed on nectar. They never bite humans.

Habitat
Crane fly larvae are found in a variety of habitats such as in ponds, marshes, and in both slow- and fast-flowing rivers and streams.
  • In the water, crane flies are 'benthic-dwelling', meaning that they live along the bottom 'floor' of the water body.
  • Benthic-dwelling crane flies can be found buried in the sand, under snags, and under or among organic material such as leaf packs and algal mats.
  • Some crane fly species do not live under water but instead live in the moist soil near the water.

Life Cycle
They undergo complete metamorphosis, meaning that they pass through four complete life stages. These are the egg, larval, pupal, and adult stages.

Eggs
  • The adult female lays her eggs directly in the water or in moist soil.
  • Egg deposition occurs very soon after mating, and the egg stage lasts one to two weeks.
Larvae
  • The larval stage can last anywhere from a few weeks to one year.
  • Longer larval life spans occur if the crane fly overwinters in larval form.
  • When overwintering as larvae, crane flies burrow into moist soil, decaying vegetation, or submerged in the water.
  • Crane fly larvae undergo four stages of development (called instars).
  • They have no legs, appear wormlike, and can be very large; sometimes up to 5 cm!
  • During the final instar, the larvae leave the water to pupate in nearby soil, moss, or leaf litter.
  • The life cycle of crane flies directly corresponds with the life cycles of its main food sources.
  • The larvae need fallen tree leaves to feed on, and must therefore mature over the fall and winter.
  • The larval stage cannot usually be seen in the spring as the larvae burrow into the sediment of the stream bed.
  • They dig deeper as the summer progresses.
Pupae
  • The crane fly larvae pupate on land, close to the water. This stage lasts for one to two weeks.
Adult
  • The adult stage only lives for a short period of time.
  • This is because its main function is to mate, and it dies shortly after mating and egg deposition.
  • Most crane fly species have only one generation per year, and are referred to as 'univoltine'.
Role in Food Chain
Crane fly larvae are very important in stream ecosystems. This is because during the process of feeding, they break down fallen leaves into smaller pieces that can then be consumed by smaller organisms.
  • Crane fly species that spend certain stages of their life cycles burrowed in the moist soil serve as prey for land animals such as spiders, centipedes, and predatory beetles.
  • Larvae that inhabit the water are prey for many aquatic animals such as fish, along with some predatory invertebrates such as dragonfly larvae.
  • As adults, crane flies make up an important source of food for spiders, praying mantises, and birds.
  • Crane fly adults do not feed on mosquitoes, but they do they bite humans.
Interesting Facts
  • Crane fly larvae can grow to be almost 5 cm (2 inches) long.
  • Larvae of some species develop a tough outer skin, which has won them the common nickname 'leatherjackets'.
  • Crane Flies are the worst fliers of all fly species. They can be 'wobbly' and fly in sporadic patterns.
  • Adults have very delicate legs which can be easily broken off.
  • Crane fly adults vary greatly in size, depending on the temperatures they encounter during development. They can range from 2 mm up to 60 mm in North America, while some species in the tropics have been recorded at over 10 cm.
  • The appearance of the abdomen can be used to determine the sex of the crane fly. Females have pointy abdomens, while those of males are blunt.
  • Adult crane flies are most active at night, although some are active in shady areas during the daytime.
  • Crane flies do not hurt humans, animals, plants, food crops or damage homes. They are still considered a nuisance, however, as a large population can cause damage to poorly-drained turf soils ie Golf courses.
  • Adult crane flies are sometimes referred to as 'daddy-long-legs', although this nick-name is also used for a certain spider species.

Sources
Absoulte Astronomy (2010). Crane Fly. Available here.
Murray Darling Freshwater Research Centre (2006). Tipulidae. Available here.
Ohio State University (2010). Midges and Crane Flies. Available here.
Texas A&M University (1999). Crane Fly. Available here
University of Kentucky Entomology (2005). Crane Flies. Available here.
Univeristy of Minnesota; Guide to Aquatic Invertebrates of the Upper Midwest (2004). Tipulidae. Available here.
DMI International Corporation (2003). LaMotte Aquatic Macroinvertebrate Insect Identification Flashcards.

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