Can a Garter Snake live off of fish and insects

Minnows & guppies r fine, as r baby mice if they will eat them. Mine do, but I had to rub guppies on them the first several times. They do not need rodents in their diet. It is optional. A diet of the right kinds of fish will be fine on its own.
Goldfish r not a good food item. They will eat them, but a long term diet of them can cause health problems due to certain vitamin deficiencies. The petstore folks will probably tell u goldfish r fine, but remember, they most likely dont actually study gartersnakes- they just work there.
Garters do not eat insects. Many will also eat slugs, worms, & frogs, although u should be careful about any wild food items as they may have been exposed to pesticides or herbicides, & wild frogs r often high in internal pesticides. I'd stick to guppies/minnows, cut up trout, or pinky mice, or a combination of those things.
If interested, here is a forum all about garters, & the people r very freindly. http://thamnophis.com/

Hope this helps.

no they do not eat bugs.but you can feed them feeder fish witch is baby gold fish.and who ever said you can not feed them that well they are wrong i had one many years ago before i turned it lose because it was hurt and i feed it feeder fish,worms and live pinkie mice from time to time.oh by the way when they bite it does not hurt one little bit.well good luck.

Garter Snake dont eat insects.minnows and guppies are fine..DONT FEED IT GOLDFISH.they also eat frog.and o heard they eat slugs.mines wont..