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If you know one thing about mosquitoes, it’s probably their lust for blood. But there’s actually one species that almost never bites, even though it can. Could finding out why help us combat blood-borne diseases?
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If you know one thing about mosquitoes, it’s probably their lust for blood. And if you know two things about mosquitoes, the second is probably that they can carry diseases, like dengue, malaria, Zika, and West Nile.

Now, the culprits here are really the female mosquitoes. While males never feed on blood, the females do so for an extra nutritional boost, in order to lay eggs. But there’s actually one species that almost never bites, even though it can.

And understanding why could help us combat these deadly illnesses. Overall, non-biting mosquitoes aren’t that special. They’ve evolved multiple times from their blood-drinking relatives.

But there’s only one mosquito species we know of that has some populations that bite and some that… just don’t! It’s called the pitcher plant mosquito — because its larvae live inside pitcher plants, where they feed on bacteria and other microscopic creatures. Then, once they develop into adults, they fly away and start looking for a spot to lay eggs.

Now, some populations of this species in the southern US have pretty high energy needs. When they transform from larvae, their ovaries are still underdeveloped, so they have to devote a good deal of their energy to producing eggs as adults. At first, that goes okay, because they still have enough energy stored from their larval stage.

But when that runs out and it’s time for the second batch of eggs, these populations need an extra boost of energy. And to get it, they resort to sucking blood. On its own, this isn’t that weird.

The strange thing is that northern populations of the same species can produce multiple rounds of eggs without any blood at all. The key is, their ovaries begin to develop much earlier in their life cycle. This means they don't need to devote as much energy to that development later — so they don’t need to go after blood for extra nutrients.

In fact, scientists observing these mosquitoes both in nature and in the lab found that they’ll snub blood when it’s offered! The researchers think it may be because blood-feeding is pretty demanding, physiologically. In their study, they observed that blood-drinking mosquitoes kick their bodies into high gear before they even take a sip — in part, because they have to be able to handle and break down some toxic byproducts from digesting blood.

The insects also produce extra odor receptors to help them hone in on their blood source. Meanwhile, in non-biting populations, the insects never have to make that kind of push… so they don’t go to the trouble. At least, that’s the hypothesis.

Besides just being fascinating, research like this could really help us solve our mosquito problems. Because even though this pitcher plant mosquito doesn’t carry deadly human diseases, it could help us find ways to curb blood cravings in other mosquito species. Like, if this business about ovary development comes down to some universal genes, modifying those genes could keep mosquitoes from biting — which would stop them from spreading disease!

This kind of approach could be a gentler, and maybe more ecologically conscious solution than some current methods of disease control — like just killing the insects. For now, scientists are still working on figuring out exactly which genes are involved in the pitcher plant mosquito. But in the long run, they might hold a key to the fight against mosquito-borne illness.

Thanks for watching this episode of SciShow! If you want to learn more about mosquito science, and what would happen if we did kill all the mosquitoes, you can watch that episode after this. {♫Outro♫}.