Well, here's a couple of quick thoughts:
1) USFWS and DNR folks will oftentimes strike up conversations in hopes of finding out who may be keeping certain wildlife illegally - this even includes sounding a bit uneducated. Stings/busts are set up in this manner and it's usually those folks who talk too much that end up getting nailed.
2) Although venom production is very complex, and in the case of gila monsters not necessarily directly linked to obtaining certain substances from the food it eats, it does require an energy source and that starts with food - w/out it, an organisms ability to generate energy to produce venom and every other bodily function becomes diminished. So, in its most simplistic terms, I suppose the USFWS employee wasn't completely wrong.
>>The other day I was in my buddy's pet store talking to him and a couple of other people. We just happened to be on the topic of Arizona's venomous snakes and also gila monsters. In walks this woman who works for Wildlife & Fisheries. I've seen her before and knew who she was. She was buying some feeders for some of her personal animals. The topic had now turned to the venom of gila monsters. She overheard and decided to get in on the conversation. This was her exact quote "Well I know that gila monsters get their venom from what they eat". Did I mention that she works in the education division?
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Rob Carmichael, Curator
The Wildlife Discovery Center at Elawa Farm
Lake Forest, IL