PRAIRIE GROVE, Ill. (AP) -- A dog in northern Illinois has discovered an extremely rare rattlesnake.

A yellow Lab named Whoop was bitten on the stomach by an Eastern Massasauga rattlesnake in Prairie Grove. The veterinarian examining the dog discovered a golf-ball-sized lump on the dog's left side late last week.

Scott Ballard is a biologist for the Illinois Department of Natural Resources. He says the Eastern Massasauga rattlesnake is critically endangered and lives in wet grassy fields.

Ballard says the snake has struggled to survive as fields are filled in for farmland or development.

It generally isn't an aggressive snake.

The dog's owner Chris Frye says Whoop is recovering. Whoop spent one night hooked up to an I-V and he's now taking antibiotics and a painkiller.