Mosquito

Mosquitoes are small dipteran insects belonging to the family Culicidae, comprising around 3,600 species. The English word derives from Spanish and Portuguese, meaning “little fly”. Recognised by their slender bodies, long legs, and elongated piercing–sucking mouthparts, mosquitoes occupy a unique ecological role as both nectar-feeding insects and, in many species, blood-feeding ectoparasites. Their evolutionary success dates back to the Cretaceous period, and they remain notable both for their ecological importance and their role in transmitting disease-causing organisms.

Structure and General Biology

Adult mosquitoes possess one pair of narrow, scale-covered wings and three pairs of long, delicate legs. Their bodies typically measure 3–6 mm in length, although larger forms exist, such as species of Toxorhynchites, which reach up to about 12 mm in length. Males and females resemble each other but differ in behaviour and diet. Both sexes consume nectar and plant juices for energy, but females of many species have specialised mouthparts that allow them to pierce skin and feed on the blood of vertebrates. This blood meal supplies proteins necessary for egg development.
Mosquitoes exhibit indirect flight facilitated by thoracic muscles vibrating within the exoskeleton. The beating of their wings can range from 450 to 600 beats per second in males. Some species, particularly in the genus Anopheles, are capable of sustained flight for several hours and can travel significant distances in a single night.

Life Cycle

Like all true flies, mosquitoes undergo complete metamorphosis with four distinct stages: egg, larva, pupa, and adult.
EggsMost species lay eggs on or near stagnant water such as ponds, marshes, rain-filled tree holes, or artificial containers. Oviposition strategies vary widely:

• Anopheles species deposit cigar-shaped eggs directly onto water surfaces.
• Aedes species lay drought-resistant eggs on damp substrates, which hatch only when flooded.
• Culex and Culiseta species produce floating rafts of eggs.
• Some specialised species lay eggs on aquatic vegetation.

Egg-laying capacity ranges widely, with Anopheles females often laying 100–200 eggs in a lifetime.
LarvaeLarvae, known as “wigglers”, are aquatic and feed on algae, bacteria, and organic matter at the water’s surface. They breathe atmospheric air through a siphon or other specialised structures and exhibit characteristic wriggling movements. Larval development progresses through several moults or instars. Some Aedes larvae can survive dry conditions for extended periods, entering diapause when their breeding sites dry out.
PupaeMosquito pupae, called “tumblers”, are active swimmers but do not feed. They breathe through respiratory trumpets and remain near the surface unless disturbed. After completing metamorphosis, the adult emerges from the pupal case at the water’s surface.
AdultsAdult males typically live for a few days to a week, while females may survive for up to three weeks depending on environmental conditions and access to food. Mating usually occurs shortly after emergence, often in male swarms during dusk or dawn. Females generally mate once and use stored sperm to fertilise multiple batches of eggs. After taking a blood meal, a female rests for two to three days while her eggs develop, repeating this cycle several times.

Feeding Behaviour and Host Interaction

Although nectar is the primary energy source for both sexes, many female mosquitoes are haematophagous. Blood meals provide essential amino acids for egg production. Some species require blood for every clutch of eggs, while others need it only after their first batch.
Mosquitoes exhibit diverse host preferences. Different species specialise in feeding on amphibians, reptiles, birds, or mammals, and shifts in host selection can influence disease transmission. For instance, Culiseta melanura typically feeds on passerine birds but may attack horses and humans when populations rise, contributing to outbreaks of equine encephalitis.
The saliva injected during feeding contains anticoagulants and enzymes, triggering characteristic itching and inflammation. In addition, the ingestion of pathogens enables certain species to transmit disease-causing organisms between hosts.

Disease Transmission and Public Health Impact

Mosquitoes are among the most significant disease vectors in the world. By transmitting protozoan pathogens and arboviruses, they contribute to a substantial global disease burden. Their role in the spread of illnesses such as malaria, filarial infections, yellow fever, and dengue fever leads to high mortality, with mosquito-borne diseases responsible for hundreds of thousands of deaths annually.
From a biological perspective, mosquitoes are classified as micropredators because they feed on larger organisms without killing them. Parasitologists, however, identify them primarily as vectors that facilitate pathogen transmission.

Host Detection and Behavioural Ecology

Most mosquito species are crepuscular, feeding at sunrise or sunset and resting during the day. Others, such as the Asian tiger mosquito (Aedes albopictus), feed aggressively during daylight hours.
Mosquitoes locate hosts using a combination of cues:

• Chemical signals, notably carbon dioxide, 1-octen-3-ol, nonanal, and sulphur-containing compounds
• Heat emitted by warm-blooded animals
• Visual cues, particularly relevant at short range

Their antennae contain numerous specialised odour receptors, many tuned specifically to detect components of vertebrate breath or skin emissions.

Ecological Roles

Beyond their role in disease transmission, mosquitoes contribute significantly to freshwater ecosystems. Larvae provide food for fish, amphibians, aquatic insects such as dragonfly larvae, and certain bird species. Adult mosquitoes also act as pollinators, particularly for plants producing nectar at dusk or in shaded habitats.