Eco Bites

Mosquitoes

Mosquitoes belong to the Insect order Diptera (meaning two-wings) of which the most well known members are flies – there are about 120 000 species in this order. Mosquitoes are in the family Culicidae which is represented world-wide, the most common species is one of the so-called “house mosquitoes”, Culex pipiens – it occurs on every continent except Antarctica.

Mosquitoes lay their eggs singly or in rafts on water, preferably water contaminated with organic matter – this could be a pond, or a container with a bit of water in the bottom; some species lay the eggs in very damp soil or in small puddles. The larvae that hatch are air-breathers, breathing from the surface through a siphon at the tail-end; they feed on organic matter in the water. The pupae are lighter and float just beneath the surface breathing through thoracic breathing horns. After hatching the adults will rest on the surface to dry and harden. The stages from egg to adult normally takes about 14 days, but it can be up to 30 days – although in some species it can be as little as 4 days. In colder climates mosquitoes will overwinter in the egg phase, in some instances overwintering takes place in the pupal phase or even as an adult. The adult’s life span can be from two weeks to two months.

Raft of mosquito eggs Mosquito larva Mosquito pupa Female mosquito feeding

In most species female mosquitoes feed on blood to support the development of their eggs. Culex spp feed on various mammals, including humans, as well as on birds. They feed at night, most often in the evening and at dawn, during the day they will rest somewhere cool, but will bite if disturbed. Mosquitoes usually fly quite close to the ground, their flying speed is only about 1-2 km/h; but they can fly up to 4 hours continuously and can travel up to about 10km in a night. They are not strong flyers, and even moderate winds will blow them long distances.

Mosquitoes locate their prey through scent; they are extremely sensitive to carbon dioxide in exhaled breath, as well as several substances found in sweat and body odours. Once they get close enough, they use the prey’s body heat to locate it.

Most mosquitoes can transmit diseases. Each female needs from one to three meals to complete development of one clutch of eggs, and they develop several clutches during a season. Feeding on more than one ‘victim’ transmits disease organisms from one to the other. However, the disease organism must be present in the host animal; at present there are no known major mosquito-borne diseases affecting humans in the Western Cape.

Mosquito control

In the past mosquitoes were controlled by spraying the water bodies they used for breeding with insecticide or oil to kill off the larvae and pupae. But this is also ecologically disastrous if used on ponds and natural water bodies as it kills off all other animals in the water, including the predators that would normally feed on mosquito larvae like dragonfly nymphs, various fish species and frogs. Spraying also has long term negative effects on the environment, and is most definitely not recommended these days.

Unless disease is a factor, the best way of dealing with a mosquito problem is using repellents or putting up mosquito netting to keep them out of residences. Most repellent insecticides used today are specific to insects and will not in any way affect humans or pets in the house; in particular the evaporative repellents (those that are plugged into a wall plug) are very effective to keep a room clear of mosquitoes.

And those midges?

One last word. Mosquitoes are often confused with adult Chironomids, commonly known as midges or ‘miggies’ (‘muggies’). These are not biting flies, but can be a nuisance as they swarm in large numbers; they form swarms day and night and are attracted to lights at night.

» Click here to read more about midges «

» Click here to read more about aquatic insects.