'Vampire' spiders use blood as perfume

Jumping spiders use blood they get from eating mosquitoes as a perfume to attract the opposite sex, researchers investigating the African spiders say.

The jumping spider, Evarcha culicivora, lives in East Africa and feeds on mosquitoes, especially those that have recently fed on blood from mammals or other vertebrates.

Spider biologist Fiona Cross of the University of Canterbury in Christchurch, N.Z., found that spiders that have recently eaten blood-engorged mosquitoes are especially attractive to other jumping spiders.

Jumping spiders are about a half a centimetre long and are so named because they can leap about 40 times their own body length. They live around Lake Victoria, the largest lake in Africa, bordering on Kenya, Uganda and Tanzania.

Jumping spiders are the only animals to indirectly feed on vertebrate blood, Cross said.

Cross and her colleagues fed male and female spiders a variety of different meals. Some were given blood-fed female mosquitoes (the researchers themselves sacrificed their blood to feed the bugs). Others were given sugar-fed female mosquitoes, male mosquitoes that eat flower nectar, or non-biting lake flies.

Preference tested

The researchers tested the preference of the spiders by measuring how long they spent near a vent carrying a stream of air blowing over other spiders with different diets.

The jumping spiders that ate the blood-engorged mosquitoes were more attractive to spiders of the opposite sex than those that had other meals.

Cross said that because blood-fed mosquitoes are the preferred meal for this species, jumping spider may be selecting their mates based on their ability to catch this prey.

The fact that spiders were only attracted to members of the opposite sex suggest that the odour associated with eating blood is associated with the odour that identifies the gender of the spider.

However, the attractiveness of the spiders quickly faded if they fasted or their diet was switched, and spiders given the sugar-fed mosquitoes found themselves more popular if they started eating the blood-fed mosquitoes.

The researchers said the next step in their research is to see whether spiders that eat blood-fed mosquitoes are more successful at mating or produce higher quality eggs or sperm.

This isn't the first time that animals have been seen using "perfume" for the purposes of mating. Male fruit flies use ginger root oil to attract mates and male European starlings add sweet-smelling plants to their nests to attract females.