My experience with multi-species cohabitation.

[Bogertophis]

Just a few more afterthoughts that I didn't have time for this morning:

Quoting ..."I live in Idaho, so reptile mites aren’t a concern"
FYI- Reptile mites are not indigenous in the U.S. They're shared among captive animals in the pet trade, & great care should always be taken to see that they are never spread to our native wildlife. So if you go into pet stores in Idaho, you can conceivably bring home reptile mites if there's any in the store on their animals, as there often is. They can sometimes hitch a ride home with you on your clothing if you've handled or been close enough to their affected reptiles, & some report they've even come home with them in the substrates they bought. But native wildlife in the U.S.- so far as I'm aware- is not known to harbor these nasty disease carriers at this time. They are a shared plague of pet stores, reptile expos, careless breeders & all the hapless pet-buyers & shoppers.


However- there's just no end to the pathogens that wild snakes can harbor (yet appear "healthy") but which can nevertheless sicken or kill non-native snakes, and vice-versa. Mixing wild-caught & captive-bred or non-native snakes is just so far off the beam I'm nearly speechless... Just like humans can get very sick & die when newly- exposed to pathogens they've never contacted previously & have no resistance for. You're playing with fire. And incidentally, this is why it's a huge no-no to release non-native species into the wild, or to release even native species after they've been exposed to others while in captivity- even when they "seem healthy". So PLEASE keep this in mind.

Snakes are very stoic, & stress is not always visible until it's resulted in disease. Stress lowers their immune function, just as it does ours. Competition for certain optimal spots causes stress, even among members of the same species that are housed together. Garter snakes prefer much cooler temps. than do BPs, so either your BP is too cool or your garter snake is much too warm- I'm thinking that it's no wonder he loves to come out.

Another big misconception you have (or had?): snakes DO NOT size up their prey- when they're hungry & they get the cues they're looking for* they just go for it. They may kill prey only to discover "oops, it won't fit". *Depending on the species, the cues may include motion, heat & odors, & if they're hungry enough, some cues may be overlooked just in case it works. So forcing an assortment of predators to live in such CLOSE proximity is a very bad idea. Accidents DO happen.

Your set-up reminds me of the old saying "I'm not completely useless, I can always serve as a bad example!"