Sounds like u have dreaded Cutworm. They can be a total disaster!!! When they get bigger they will chew around the main stem of small plants until they fall over dead. They only attack at night, so if u are finding some during the day I bet they are plentiful.
BT does work, but it can be very stressfull to certain strains, mainly indicas. I would apply at less than recomended dosages if u decide to stick with it.
IMHO, there are much more reliable organic methods and Im not an organic person, I grow with chemicals, so Im not just saying this.
Dry Corn meal circled around the main stem will help, it must stay dry. They eat the cornmeal and it expands in their stomach and they die.
What I did was made plant protectors. U can use a toilette paper roll (for small plants u can slip it over the plant, for larger plants u have to cut the roll and then tape it shut after it is around the plant) , or anything that u can make into the shape of a toilette paper roll, center it around the main stem, making sure it is not touching the stem but it is about a centimeter or two away from the stem on all sides . Then u bury it one inch into the soil, leaving 2 inches above ground.. Pics and more tips are on the web if u look up homemade cutworm traps.