YORK, Pa. (WHTM) – A helicopter will be flying across Pennsylvania communities on Monday conducting spraying for flies.

The York County Office of Emergency Management says Helocopter Applicators Inc. will be dispersing Vectobac 12AS, a bacterial larvicide, for black fly (gnat) suppression.

Vectobac 12AS is not a chemical and is a thick brown liquid resembling chocolate milk. The Office of Emergency Management says Vectobac 12AS is a Bti product, which stands for Bacillus thuringiensis var. israelensis, and is the “only product used in Pennsylvania’s waterways for black fly suppression.”

You may see the helicopter in areas including York near creeks with a tail number of N651HA. It’ll be flowing low near tree tops and releasing the Vectobac in predetermined locations on creeks.

The spraying began at 7 a.m. on Monday.