Seven things worth knowing about mosquitoes

Anopheles Gambiae, one of three mosquitoes found in Africa that transmit malaria. shutterstock

This article is part of a series The Conversation Africa is running as part of the South African Development Community malaria week. You can read the rest of the series here.

1. Not all mosquitoes bite.

The female mosquitoes are the dangerous ones. They bite and draw blood. Male mosquitoes feed on flower nectar. Males have very hairy and fuzzy antennae (like a powder puff) whereas females have less hairy antennae.

2. There are three types of malaria carrying mosquitoes.

The top three malaria transmitters in Africa are Anopheles gambiae, Anopheles funestus and Anopheles arabiensis. The first two live in areas of Africa where there is higher rainfall while the third, Anopheles arabiensis, is a more savanna-based, arid zone species.

Gambiae and funestus prefer to feed indoors and are strongly attracted to humans, but arabiensis feeds as easily outdoors as indoors and also as easily on cattle and other animals as humans. This means it is easier to target gambiae and funestus using indoor methods such as spraying walls with insecticides and using insecticide-impregnated bed nets. The outdoor-feeding arabiensis is far more difficult to control.

In most areas all three species have a peak of biting in the early hours of the morning when people are in their deepest sleep and less likely to disturb mosquitoes during the feeding process. There are also other important species of malaria-transmitting mosquitoes but they are more localised in distribution.

3. Mosquitoes have started to change their feeding patterns.

Because of the strong focus on indoor strategies to fight malaria transmitting mosquitoes using bed nets and indoor spraying, genetic selection is resulting in some populations of these mosquitoes biting outdoors and earlier at night when people are not protected by bed nets. It means these mosquitoes are more difficult to reach with insecticides, just as is the case with Anopheles arabiensis.

4. Most mosquito bites are harmless. It’s only the ones that carry certain types of parasites that lead to malaria, and potentially death.

In Africa, there are four known species of microscopically small parasites that can cause the disease we call malaria. All four belong to the group Plasmodium. The most common of these parasites in Africa is Plasmodium falciparum, which is the most deadly of the four species.

Birds and some other groups of animals carry their own species of Plasmodium, which is also transmitted by mosquitoes, but they do not cause malaria in humans. Mosquitoes also carry many other disease-causing organisms such as yellow fever virus, West Nile virus, Rift Valley fever, and the worms that cause the dreaded disfiguring elephantiasis (filariasis).

5. Mosquitoes select where they feed on the body. They have very acute sensory mechanisms (like heat-seeking missiles) that lead them to select particular parts of the body (such as ankles) to feed from.

All three of the main malaria carrying mosquitoes have similar biting preferences. If you are sitting or standing outside in the evening the overwhelming majority will try to feed on your ankles and feet - so make sure you cover these areas with repellent or wear socks and shoes.

The antennae of mosquitoes are highly specialised sensory organs that can detect very small amounts of chemical cues that lead them to food and mates. Various chemicals, of which carbon dioxide is one, help female mosquitoes track down their hosts. Pheromones, which are hormones secreted as odours into the environment, enable males and females to meet and mate. They are also detected by the antennae.

6. Malaria mosquitoes do not like wind.

Using a fan over you when going to bed will lessen your chances of being bitten. These mosquitoes don’t like flying when there is even a slight breeze.

7. 97 countries and territories still face ongoing malaria transmission.

According to the World Health Organisation, an estimated 3.2 billion people, or just under half the world’s population, are at risk of getting malaria. The bulk of the malaria burden is shouldered by Africa where 89% of cases and 91% of deaths occur.