Could be nudis. You would see them, especially at night. Anything nearby that could sting it? Anything get dropped on it? I've had nudis. If they are there, you'll know soon enough. They are easy to see wiht the naked eye, especially when they get big. Look like little white hairy demons, LOL! If you have other montis that are doing good, may want to get this out and dip ASAP.