for National Geographic News
Scientists have discovered a spider in East Africa with a craving for human blood.
They say the spider, which hunts blood-sucking female mosquitoes, is the only animal known to select its prey based on what the prey has eaten.
The spider is the also first known predator that deliberately feeds on vertebrate blood by eating mosquitoes.
The finding raises the possibility that other spiders also have a taste for human and mammal blood, the researchers add.
The blood-hungry spider, Evarcha culicivora, is found only around Lake Victoria in Kenya and Uganda. A species of jumping spider, or salticid, it usually hunts insects on tree trunks and buildings. It stalks its prey rather than trapping it in a web.
The study team says the jumping spider uses both its acute eyesight and its sense of smell to seek out the mosquito Anopheles gambiae, a notorious blood-sucker that is the main carrier of malaria in Africa.
The team's findings are published this week in the online edition of Proceedings of the National Academy of Sciences. The research was partly funded by the National Geographic Society.
Smell of Blood
Lab experiments conducted near Lake Victoria showed the spider preferred female mosquitoes fed with human blood over all other prey, including male mosquitoes, which don't feed on animal blood.
Tests of the spider's prey preferences showed it went for blood-engorged female mosquitoes in 83 percent of cases when offered a choice of two similar-size insects.
When it came to making a choice based on smell alone, with the two meal options hidden from view, around 90 percent of jumping spiders selected the blood-filled mosquito.
Although no other predators are known to choose prey based on the prey's last meal, other spiders may also select their victims this way, says study co-author Ximena Nelson, who conducted the research while at the University of Canterbury in New Zealand.
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