The different species of the Anopheles gambiae  complex (or Anopheles gambiae sensu lato) have in common a very similar, almost identical morphology: there are referred to as twin species. Determination within the complex is based essentially on three criteria:

- Criteria of reproduction in an insectarium, with reference species. Crosses between different species give birth to hybrid but sterile live males. On the contrary, the females, even hybrids, are perfectly fecund.
- Cryogenetic criteria using the sequence of light and dark strips of special chromosomes, the giant chromosomes or polytenes. These chromosomes are observed either in the salivary glands of the larvae, or in the food cells of the ovaries of the semi-gravid female.
- Molecular criteria, such as the polymorphism of the length of microsatellite DNA sequences revealed by the PCR technique. 

Seven species are to be found in this complex, all of which are African: 

Anopheles gambiae sensu stricto and Anopheles arabiensis present the greatest areas of distribution.

Distribution of Anopheles gambiae
and Anopheles arabiensis

(source : J. Brunhes et al.,
Les anophèles de la région afro-tropicale,
software ORSTOM Ed., 1998) 

These two species live almost everywhere in the northern part of Sub-Saharan Africa. They are not to be found at altitudes in excess of 1,000 meters. Anopheles arabiensis is absent from the dense forest areas. These two species have a large ecological amplitude. Classically, Anopheles gambiae dominates in forest and damp savannah zones, whereas Anopheles arabiensis is more at home in the drier savannas, the steppes and at times the towns, especially in Southern Nigeria..

The larval breeding grounds are relatively shallow collections of water, well-exposed to the sun: footprints, puddles, small ponds, managed marshlands, rice paddies, residual puddles from watercourses following the drop in water levels after flooding. The Anopheles gambiae and Anopheles arabiensis  larvae are also to be found in other types of breeding grounds, but more rarely. They are rarely to be found in heavily shaded, alkaline or polluted waters, or where there is a strong current,.

The density of the populations varies according to the rainfall. Thus, in savanna areas with just one rainy season, it increases rapidly with the first rains and the maximum density is reached in the second half of the rainy season. It subsequently decreases.

The females bite preferably at ground level, inside houses (this is referred to as an endophagous bite). But exophagous bites are not rare, in particular among the Anopheles arabiensis. The two species are extremely anthropophilic, except when there is an abundance of cattle in the vicinity (especially bovines, but also goats and sheep) when they become zoophilic. Classically, the biting activity increases during the first half of the night, reaches its maximum level between midnight and four in the morning, then subsides, persisting until dawn. 

Anopheles arabiensis and especially Anopheles gambiae like to spend their time within dwellings (this is referred to as endophily). Endophily-exophily is variable according to the season, the trophic preferences, the habitat, etc. Generally, endophily is preferred in the cold season, anthropophilism and the arid zones without favorable places outside for their daily rest. 

The active dispersion is around 2 km. The gonotrophic cycle lasts three to five days for the nulliparous females and from two to three days for the parous females
Among the other species of the complex, only Anopheles bwambae, Anopheles melas and Anopheles merus play a role, albeit secondary, in the transmission of malaria. Anopheles bwambae is found in the forest of Uganda, Anopheles melas on the Atlantic coast littoral, Anopheles merus on the Indian Ocean coast. These three species use larval breeding grounds with a high salt level: the Anopheles bwambae larvae develop in mineral water springs, those of Anopheles melas and Anopheles dirus in brackish water (lagoons). 

Distribution of Anopheles melas

(source : J. Brunhes et al.,
Les anophèles de la région afro-tropicale,
software ORSTOM Ed., 1998) 

Distribution of Anopheles merus

(source : J. Brunhes et al.,
Les anophèles de la région afro-tropicale,
software ORSTOM Ed., 1998)

The species Anopheles funestus is spread throughout the whole of Sub-Saharan Africa. It is abundant in the open savannas. It reaches 2,000 meters in mountainous regions, where its density is often greater than that of Anopheles gambiae s.l.

Its larval breeding grounds are typically in clear, permanent or semi-permanent deep waters, shaded by vegetation (grasses, floating vegetation). These are ponds, marshes, the edges of lakes and water courses. Rice paddies are used by this mosquito in East Africa and Madagascar, but not in West Africa.

The density of the imaginal population varies with rainfall, but with a certain delay compared with Anopheles gambiae s.l.. This delay is due to two factors: one the one hand, the conditioning of the deep water breeding grounds, and on the other hand, the relatively slow pre-imaginal development. In savanna areas, the density of the adult populations increases well after the beginning of the rains and reaches its maximum at the beginning of the dry season, at the moment when the Anopheles gambiae s.l. populations have already considerably reduced. In more regularly and better-watered forest areas, the densities are more stable and generally lower. 

This species, like Anopheles gambiae and Anopheles arabiensis, much prefers to bite Man, but a certain opportunism tends to increase their zoophilism when there is an abundance of sensitive cattle: this is referred to as trophic deviation. Endophagous biting  is very noticeable. Generally, the biting activity starts at dusk and reaches its maximum in the final four hours of the night. In the cold season, this peak is to be found at the start of the night, despite a very small drop in temperature.

The females usually rest inside dwellings. However, the nulliparous females are more exophilic. The gonotrophic cycle generally lasts four to five days with the nulliparous females and two to three days with the parous females. The flight distance between biting and egg laying is around 2 km, but it may reach 7 km. 

Distribution of Anopheles funestus

(source: J. Brunhes et al.,
Les anophèles de la région afro-tropicale, 
software ORSTOM Ed., 1998) 

Another species belonging to this group, Anopheles rivulorum, albeit slightly anthropophilic, has proven to be a malaria vector in Tanzania. 

Anopheles nili   is very widely spread throughout Africa and is located around permanent or semi-permanent water courses in which the larvae develop. 

In savanna areas, it is abundant during the second half of the rainy season. Along the Congo river, its maximal density is observed during the dry season, with the larvae carried away by the current in the rainy season. Along the Sanaga river, in the south of the Cameroon its density is proportional to the flow of the river. 
This species bites Man in preference. The biting activity becomes fairly rapidly obvious as night falls and has a more precocious peak than those of Anopheles gambiae and Anopheles funestus. Anopheles nili is much more ectophagous and exophilic than the latter pair.

Distribution of Anopheles nili

(source : J. Brunhes et al.,
Les anophèles de la région afro-tropicale,
software ORSTOM Ed., 1998) 

Anopheles moucheti  is limited to the forest area of Central Africa and to the forest galleries which extend it to the North and especially to the South. It is known in the South of the Cameroon, in Gabon, in the south of the Central African Republic as well as in the Congo. The larvae are to be found along the relatively wide watercourses,  in apparently motionless waters where the vegetation is abundant. In the vicinity of the villages, the adult females bite as much inside as outside the dwellings, throughout the night. Exophily is often very noticeable. 

Distribution of Anopheles moucheti

(source : J. Brunhes et al.,
Les anophèles de la région afro-tropicale,
software ORSTOM Ed., 1998)