Bill Gates called mosquitoes “the deadliest animal in the world” for their incessant spreading of deadly diseases like malaria, which killed an estimated 429,000 in 2015 alone. Nearly half the world lives at risk of the disease, said the World Health Organization, which made the estimate.

Depending on where you live, mosquitoes may range from an itch-inducing annoyance to a constant threat. That’s led scientists to ask: What if we killed them all?

We just don’t know, many of those experts have concluded. But they can imagine.

More than 3,500 mosquitoes species exist, but only a few affect our health. The Anopheles gambiae carries malaria, for example. The Aedes aegypti came to the U.S. aboard slave ships, spreading yellow fever and, as seen last year, Zika.

So we need not end all mosquitoes to reduce mosquito-related deaths, as Cameron Webb, an etymologist at the University of Sydney, told Motherboard last year. And that may be preferable, said Webb, who had “little doubt” their full extinction could have indirect effects.