Life Science

Evarcha culicivora – A Spider With A Taste for Blood

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 jumping spider (Evarcha culicivora) eating a mosquito
The “vampire spider” (Evarcha culicivora) Photo Credit: Robert R. Jackson
The vampire jumping spider (Evarcha culicivora) eating a mosquito
The “vampire spider” (Evarcha culicivora) uses mosquitos as a source of vertebrate blood. Photo Credit: Robert R. Jackson

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.

Evarcha culicivora photograph taken during an experiment
Evarcha culicivora photograph taken during an experiment. Photo Credit: Robert R. Jackson

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

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