It’s no mystery that spiders have a penchant for liquid food; that is how they eat after all. But what about a spider with a particular affinity for the blood of vertebrates? We’re not talking about the spiders that catch bats or the Goliath Bird-Eater (Theraphosa blondi) which enjoy whole vertebrates (so to speak), but rather one that is after vertebrate blood specifically.
Meet Evarcha culicivora, known colloquially as the “vampire spider”, which inhabits the area around Lake Victoria in Kenya and Uganda. E. culicivora is a member of the Family: Salticidae (jumping spiders), a group of generally diurnal hunters with very well-developed visual capabilities which capture prey by…well…jumping on it. By altering the pressure of the hemolymph within their legs, they are capable of making bounds several times their body length with amazing speed and accuracy.
In the case of E. culicivora, the prey of choice is mosquitos and not just any mosquitos, but female mosquitos which are full of vertebrate blood from a recent meal. Research has shown that the spiders use a combination of visual cues (specifically mosquito abdominal and antennae morphology) and olfactory signals to help them discern full female mosquitos over other available prey items like male mosquitos, empty female mosquitos, and midges. Furthermore, it is has been shown through miscroscopy that once the spider captures the full mosquito, it prioritizes the fresh blood within the unfortunate mosquito rather than the mosquito as a whole.
This is also not a matter of simply taking advantage of the fact that freshly-fed female mosquitos are a little clumsy or the fact that all spiders appear have an evolutionary drive to preference prey items which optimize their amino acid intake. Rather, it appears to be a very clear affinity for vertebrate blood meals that it would otherwise not be able to obtain without the mosquito actings as an (unwilling) intermediary transporter (sort of like a flying, blood-filled tanker truck).
But why the love of blood? As with many animal behaviors, research seems to point to mating as a key underlying motivator. It turns out that when an E. culicivora consumes a blood meal, it becomes significantly more attractive to members of the opposite sex and thus increases its chances of successfully securing a mate. This attractiveness apparently comes in the form of an odor produced by the spiders after blood-meals, though the exact molecular signature of the odor seems to be unknown at this time.
So the next time you are bitten by a mosquito while visiting Lake Victoria, know that aside from possibly getting malaria, you may also very well be helping two lonely, lovesick, blood-thirsty E. culicivora find one another.
- Cross, F. R., Jackson, R. R., & Pollard, S. D. (2009). How blood-derived odor influences mate-choice decisions by a mosquito-eating predator. Proceedings of the National Academy of Sciences, 106(46), 19416-19419.
- Jackson, R. R., Nelson, X. J., & Sune, G. O. (2005). A spider that feeds indirectly on vertebrate blood by choosing female mosquitoes as prey.Proceedings of the National Academy of Sciences of the United States of America, 102(42), 15155-15160.
- Nelson, X. J., & Jackson, R. R. (2012). The discerning predator: decision rules underlying prey classification by a mosquito-eating jumping spider. The Journal of experimental biology, 215(13), 2255-2261.