A species of spiders found only around Lake Victoria in East Africa, called Evarcha culicivora, is adapted to hunt female Anopheles mosquitoes that transmit malaria parasites.
“This is unique. There’s no other animal that targets its prey based on what that prey has eaten,” says Fiona Cross, an arachnologist at the International Centre of Insect Physiology and Ecology (icipe) in Kenya, who co-authored a study on the spiders.
“This is unique. There’s no other animal that targets its prey based on what that prey has eaten.”
Fiona Cross, International Centre of Insect Physiology and Ecology
Cross says that these spiders “love” feeding on human blood as it gives them an odour that renders them sexually attractive to potential mates.
But the spiders pose no danger to humans, the researchers say. Even though the spiders like human blood, they lack specialised mouth parts to pierce people’s skin. Instead, to get the nutritious blood meal, the spiders feed on the female mosquitoes that carry blood they suck from humans.
“Their compound eyes give them clear eyesight. And just like a cat, they stalk their prey and pounce on them at the right moment,” she says.
The study, published in the current issue of Journal of Arachnology, says that the spiders identify female Anopheles mosquitoes through their up-tilted abdomens — a resting posture they adopt after feeding on human blood.
Another species, from Malaysia, P. wanlessi also specialises in eating mosquitoes, but it prefers to live in bamboo culms and likes to feed on mosquito larvae lurking in pools of water.
In contrast, E. culicivora spiders live on walls of people’s homes. Cross urges communities to embrace the spiders to harness their potential in malaria control, but she understands that many people loathe spiders and would need time to accept them.
“People need to know that these organisms are harmless and will not attack them,” Cross says. The World Health Organization (WHO) estimates that malaria causes over half a million deaths annually, mostly among African children. But between 2000 and 2013, death rates have fallen by 54 per cent in Africa as a result of several malaria control interventions.
Njagi Kiambo, a malaria expert at Kenya’s Ministry of Health, says that since malaria is a complicated disease, it cannot be fought using a single approach.
Kiambo advises that biological control methods embracing mosquito eaters – such as ticks, lizards, crustaceans or fish – should be encouraged. “But we cannot solely rely on them as their impact is minimal compared to chemical interventions like insecticides put on bednets,” he says.