Pond educational resource pack

CORNWALL

Flies

A true fly is distinguished by the possession of only one pair of wings, instead of the two pairs more normal in flying insects. No flies live in water as adults, but many of their larvae do.

A drone-fly is so called because it mimics a male Honey Bee. Its larvae thrive in stagnant waters with abundant rotting plant material. The larva lives within and feeds on this. In such conditions oxygen is scarce, so the larva extends a telescopic breathing tube towards the water’s surface. Its appearance earns it the delightful name of rat-tailed maggot.

Some species of horse-fly have aquatic larvae which crawl about in the mud, chewing up worms, crustaceans and insect larvae mainly but in some cases decaying plant matter. They are tapered at both ends and push their short breathing tubes through the water’s surface when they rise for air.

The larvae of crane flies, or daddy-long-legs flies, are sometimes called leather jackets because of their tough skin. Some species lay their eggs on land, giving rise to larvae which can be serious pests eating the roots of grass and crops. Those larvae which live in water are mainly scavengers of decaying plant material in the bottom mud. They surface tail-first to take in air, like many other aquatic insect larvae.

A phantom crane-fly larva differs from that of a true crane-fly in having one end of its body drawn out into a long extensible breathing tube. Larvae in this family are usually buried in the mud, where they feed on decaying plant material.

The mosquitoes form a large family of flies in which the females suck blood, which they need to nourish their developing eggs. The larvae of Culex mosquitoes can be found hanging at an angle, each attached to the water surface by a breathing tube. Anopheles mosquito larvae lie along the water surface and breathe without the aid of tubes. This latter type of mosquito includes species which can carry malaria, and which did so in Britain in former times. A mosquito larva has bristles on its mouthparts which stir up a current, carrying water from which microscopic living organisms are filtered out as food. The large-headed pupae of mosquitoes are unusually active for pupae - both larvae and pupae can dive to escape danger.

Midges are similar to mosquitoes, but not all of them bite. It should be noted that the word "midge" is a general term people use for small flies in various families, sometimes including mosquitoes, and has no precise meaning. Some people use the word "gnat" in the same way. Chironomids, dixids and phantom midges are all commonly occurring groups of non-biting midges.

Chironomid larvae are often red in colour, in which case they are called bloodworms. Their colour comes from a blood pigment similar to our own, which helps them to absorb as much as possible of the limited oxygen in the mud where they live. The larva often constructs a tube through which it makes a current flow by waving its body. Oxygen and tiny particles of food are extracted from the current. A chironomid pupa can be distinguished from those of other midges by the feathery tufts on its head. Dixid midge larvae and pupae are characterised by their U shape when at rest. The larva lies at the waters surface, vibrating the bristles around its mouth to cause a current from which minute food particles can be filtered.

Phantom midge larvae and pupae are difficult to see, as their bodies are very transparent. At rest the larva hangs under water, parallel to the surface. When disturbed it moves rapidly by sudden flicks of its body. It feeds by snatching small insects and crustaceans as they swim by.

Drone-fly Larva (Rat-tailed Maggot)	Horse-fly Larva

[15mm (75mm with tube extended)]	[Up to 25mm]
Crane-fly Larva	Dixid Midge Larva

[Up to 50mm]	[4-8mm]
Black-fly Larva	Phantom Crane-fly Larva

[Up to 10mm]	[Up to 35mm]
Phantom Midge Larva	Culex Mosquito Larva

[Up to 14mm]	[Up to 10mm]
Anopheles Mosquito Larva	Culex Mosquito Pupa

[Up to 10mm]	[Up to 10mm]
Chironomid Midge Larva	Chironomid Midge Pupa

[Up to 30mm]	[Up to 30mm]