Spiders obviously have a penchant for liquid food. Usually, that takes the form of dissolved invertebrate insides, but at least one spider has 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, but rather one that is after vertebrate blood specifically.
The “Vampire Spider”
Meet Evarcha culicivora, known colloquially as the “vampire spider.” This little arachnid 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 used to help them stalk and ambush prey. By altering the pressure of the hemolymph within their legs, they can make spring forward in leaps several times their body length.
In the case of E. culicivora, the prey of choice is female mosquitos full of vertebrate blood from a recent meal. Research has shown that the spiders use a combination of visual cues (e.g. mosquito abdominal and antennae morphology) and olfactory signals to help them distinguish full female mosquitos from other available prey items like male mosquitos, empty female mosquitos, and midges. It has also been shown through miscroscopy that once the spider captures the full mosquito, it prioritizes the fresh blood within the abdomen rather than the mosquito as a whole.
These spiders aren’t simply taking advantage of the fact that freshly-fed female mosquitos are a little clumsy or the fact that all spiders appear to prefer prey items that optimize their amino acid intake. Rather, it appears to be a very clear affinity for vertebrate blood meals – meals that it would otherwise not be able to obtain without the mosquito actings as an intermediary.
What’s with the Blood Fixation?
But why the love of blood? As with so many behaviors, research points to reproduction as a key underlying motivator. It turns out that when E. culicivora consumes a blood meal, it becomes significantly more attractive to members of the opposite sex. That 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.
You read that right. Blood cologne.
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 E. culicivora find each other. Adorable.
Further Reading
- 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.