A new study found that honey bees have been dying due in part to a Monsanto product called Roundup, which is a weedkiller that contains a chemical that is deadly to bees.

The study was released today and it found that the weedkiller contains glyphosate, which is a chemical that lowers the amount of microorganisms in honey bee guts. This worsens the creatures’ immune systems, thus leaving them more susceptible to die from natural causes.

Nancy Moran, the senior author of the study and evolutionary biologist with the University of Texas, said that honey bees that were exposed to glyphosate on a regular basis had a lower amount of microbiota in their gut, which highly increases their chances of dying early.

“Gut microbiota is involved in nutrition for bees, helping break down components of cell walls in pollen grains and protecting against different pathogens,” she said. The health of honey bees is directly linked to how healthy these organisms in their gut are.

These microbiota help to improve bees’ metabolism, while also helping them gain weight and bolster their immune system. Monsanto had previously claimed that glyphosate does not hurt wildlife, but the new study from the University of Texas shows that this isn’t the case.

The researchers collected hundreds of honey bees from a single hive and exposed them to glyphosate, finding that they were more likely to die when exposed to the chemical.