Insecticide resistance is growing; ‘biological control’ of mosquitoes is becoming more commonplace in response. Communities are increasingly employing small creatures to help in their fight against dengue. Previously, we’ve looked at how people in Cambodia have used guppy fish, and also tried using crustaceans, to help reduce Aedes mosquito numbers.
A recent study decided to review a completely new type of biological mosquito control: mosquito-eating spiders!
Spiders as mosquito predators
You may well be asking yourself why the team from the Bindura University of Science Education in Zimbabwe specifically chose to examine this particular creature. Their research paper explains: “Spiders have a wide insect host range and thus can act as biological control agents of insect pests.”
With various species of spider known to prey on different species of mosquito, the paper goes on to note: “Spiders have largely been overlooked as predators of mosquitoes and its larvae in various ecosystems, yet they play an important role as stabilizing agents or regulators of insect populations in agro-forest and other terrestrial ecosystems.”
Aiming to get a better understanding of how spiders and mosquitoes interact, the team examined previous research into mosquito-eating spiders. They looked at both web-building spiders and hunting spiders, some of which actively search and chase mosquitoes as well as ones that lie in wait and seize their prey.
The East African mosquito-eating jumping Evarcha culicivora spider targets its prey based on their last meal. Commonly known as the ‘vampire spider,’ it has a distinct liking for adult female mosquitoes with a belly full of human blood.
To decide whether a particular mosquito is worth pursuing, the spider uses its unique, complex eyes to “see prey in remarkably fine detail” along with olfaction (sense of smell) to work out whether a mosquito “has just taken a blood meal based on the tilt of their abdomens.” If the prey looks interesting, it “pounces,” the researchers reveal.
For these particular mosquito-eating spiders, eating blood-filled mosquitoes isn’t just about nutrition – it’s also about sex. According to the study, eating blood-filled mosquitoes gives them a “perfume” that makes them more attractive to a potential mate.
Also from the same Salticidae spider family but this time found in Southeast Asia, the Paracyrba wanlessi “lives in the hollow internodes of fallen bamboo,” note the team. Unlike E. culicivora, P. wanlessi doesn’t have a preference for the age or sex of its prey – or what’s in its belly.
Weaving a mosquito trap
The team also looked at mosquito-eating spiders from the Pholcidae family. The long-legged Crossopriza lyoni is a common inhabitant of homes in the rural villages of Thailand “where dengue fever, transmitted by the Aedes aegypti mosquito is endemic,” states the report.
After moulting, young spiderlings are already able to overpower the adult Aedes aegypti mosquito, even though it is “many times their own size”. The spiders use their hind legs to throw silk, immobilising the mosquitoes by “entangling them in the standing web”. The report suggests “C. lyoni could be an important component of integrated control of Aedes aegypti and help reduce dengue transmission.”
The review concludes that “spider predation could be of great ecological significance in suppressing mosquito populations. Management of spider populations could provide the
additional control of adult mosquitoes needed to reduce the transmission of mosquito-borne diseases.” Its final recommendation is rather startling: “Perhaps, it would behove human communities to foster
spiders in and around their homes.”
Would you introduce spiders or other biological mosquito controls in your area?