Mosquitoes belong to a family of flies called Culicidae. There are over 3,000 species of mosquitoes worldwide and 300 species in Australia.
Although mosquito species are very diverse in habits, behaviour, flight range, diet, habitat and impact on humans, all species do share some characteristics. They are all small slender insects with 6 legs, 2 scale-covered wings and have a four stage life cycle – egg, larva, pupa and adult, of which the first three stages are aquatic, only the mature adult is terrestrial.
Mosquito eggs are laid in an aquatic habitat, the emerging larva are legless, segmented with well developed heads and mouth brushes for feeding on algae, bacteria and microbes. They feed continuously and grow through four different instars or moults. The final instar develops into a comma shaped pupa which floats on the water surface until the adult insect emerges.
The male and female of all mosquito species consume sugary fluids such as nectar, but it is only the female of the parasitic species which will seek a blood meal as a protein source for egg development.
These female mosquitoes have receptors which enable them to locate a potential host by detecting carbon dioxide, scent, air movement and heat. They can respond to the slightest amount of exhaled carbon dioxide and the olfactory receptor neurones in their antennae sense a wide range of chemicals, however it is the host's nonanal, a powerful semiochemical, that seems to provide the strongest trigger which leads a mosquito to its host and bite site.
The mosquito pierces the host's skin, taps into an underlying blood vessel and pumps up the blood which is stored in the mosquito's abdomen, once the storage capacity is reached the mosquito withdraws and flies away.
The female's specially adapted mouth consists of a sheathed proboscis enclosing six specialised parts. Two pointed mandibles and two blade like maxillae are rocked back and forth to pierce the host's skin; the hypopharynx and labrum are hollow structures which are pushed down into the wound where they form a closed tube. The mosquito then injects its saliva, a complex fluid containing a mix of proteins, anticoagulant, antiplatelet and vasodilatory agents to promote blood flow and prevent disruption to feeding by the host's immune response.
Some saliva always remains in the wound, its proteins promote an immune response which causes inflammation and itching until the immune system breaks down the saliva proteins.
Mosquitoes can be vectors of some diseases. When they bite hosts infected with certain viruses and parasites, the insect acts like a contaminated syringe and transmits the damaging organism from host to host without exhibiting symptoms itself.
Mosquitoes use their beating wings to create their characteristic whine which is part of an acoustic courtship, male and females adjust their pitch until they harmonise at about the same frequency of 1,200 hertz.
Although always irritating, and sometimes dangerous, these minute lady vampires are remarkable creatures.