Researchers are warning that firefly populations are dying out and that human causes are to blame, according to an article by the Asbury Park Press.

The article reports that large-scale construction and development projects have decreased their marsh and wetland habitats, with further threats posed by the use of pesticides and weed killers.

While there is not yet quantitative data to determine population loss, entomologist Christopher Heckscher with Delaware State University says that certain firefly species common several decades ago are now nowhere to be found.

Ben Pfeiffer, a master naturalist who founded firefly.org, said he began to notice certain populations were disappearing near his home in south Texas back in 2008. He says the issue is not just about a decline in terms of numbers but that there’s less firefly diversity than there used to be.

There are roughly 2,000 firefly species around the world, with 200 of those detectable in the U.S. Adult fireflies only survive for a few weeks and must mate during their short lifetimes. They spend up to a year in larvae form, eating slugs and snails while living on the ground.

Lightning bug populations often reflect the environment around them, and while no one knows for sure what is causing population drops, researchers suspect light pollution is also to blame. Researchers say that the use of pesticides and weed killers can also threaten their young forms.