As a child, the mere glimpse of a spider used to send me screaming and running for cover. I was convinced that spiders were my enemies. I thought they were out to get me.
These days, I run towards spiders, not away from them. I can partly thank a spider for helping me with that. This is a special spider affectionately known as the mosquito terminator.
Mosquito terminators (Evarcha culicivora) are small spiders, about 5mm long. They are a species of jumping spider from the family Salticidae, the largest family of spiders. Like all jumping spiders, these little predators have good eyesight and they hunt for their prey like stealthy cats.
Jumping spiders live almost everywhere around the world (even on Mount Everest) and they are found in a variety of shapes, sizes and colours. The quickest, most convenient way to identify a jumping spider is simply by looking at it: if it looks back at you with two big eyes in front of its face, it’s a jumping spider.
Most jumping spiders mainly eat insects. Mosquito terminators are no exception, eating a wide range of insects. But they do have a distinct prey preference. Just like Arnold Schwarzenegger of The Terminator fame, these little predators are on a mission to seek and destroy — in their case, they target mosquitoes.
Fiona Cross, CC BY-NC-ND
Mosquito terminators take this preference to an extreme. They particularly like the mosquitoes they eat to be full of blood. If they are presented with a blood-carrying mosquito alongside another kind of insect, even a mosquito not carrying blood, they will choose the blood-carrying mosquito nine times out of ten.
Blood-carrying mosquitoes are an important part of this spider’s diet. They can also help mosquito terminators attract mates. After dining on a blood-carrying mosquito, these spiders acquire a blood perfume that then attracts the opposite sex.
An antidote to malaria?
These spiders are found in the Lake Victoria region of Kenya and Uganda. Mosquito-transmitted diseases, such as malaria, are prevalent in this part of the world. These diseases kill hundreds of thousands of people each year.
Anopheles mosquitoes, which can transmit malaria, are known to be anthropophilic – they like being in the company of people. They are attracted to our breath and the smell of our feet. Being near us helps these mosquitoes to find blood meals.
Mosquito terminators also live near people, and it turns out they like the smell of our feet, too. Just like Anopheles, these spiders are more attracted to our previously-worn socks than to unworn socks. Mosquito terminators are currently the only spiders known to be anthropophilic. Being near us might help these spiders to find their favourite prey.
My research has further investigated this prey preference and how these spiders use their tiny brains. Amazingly, they can identify a blood-carrying mosquito by either smell or sight, even if they have never eaten or seen a mosquito before. This suggests that their penchant for blood-carrying mosquitoes is hard-wired or innate.
Fiona Cross, CC BY-NC-ND
My research has also explored whether the colour red is of special importance to these spiders. The redness of a blood-carrying mosquito darkens over time as the blood gets digested. This darker colour becomes less attractive to these spiders.
The importance of redness extends to the spiders’ bodies too. A female mosquito terminator is mostly brown in colour, but the males have little bright red faces. Cover that bright red face with black eyeliner, and males are less certain that they are encountering a potential rival. Females are also less inclined to choose a male with a concealed red face, preferring those with bright red faces instead.
Mosquito terminators are not harmful to people and nor are they vampires – they cannot bite us directly to drink our blood. They also cannot rid the world of malaria. For one thing, releasing mosquito terminators in different habitats will not work. Yet these and other jumping spiders play an important role in nature. So, next time a spider turns and looks back at you, watch closely – your new eight-legged friend may be a jumping spider.
Fiona Cross receives funding from the Royal Society of New Zealand Marsden Fund.