I am positive that venoms can vary from location to location.

In SoCal there are isolated populations of Southern Pacific Rattlesnakes whose venom evolution is off the chart. Some groups have more myotoxins and neurotoxins than others. Arizona's rattler populations are also suspect. Both CA and AZ have had cases where Crofab (anti-venin) almost wasn't enough to combat the new strains.

Here in the Northwest we also have varied populations of newts and common garters that have unique co-evolutionary toxins and immunities. Interestingly, in some spots common garters have a low immunity to the toxic effects of eating newts; concurrently these newts tend to be less toxic (no need to produce more toxins if the snakes can't deal with it in the first place). In some areas however, garters have evolved a high level of immunity and do survive eating newts; concurrently these newts are usually highly toxic. It's an arms race, and there are trade-offs. Newts that produce more defensive toxins produce fewer eggs. Garters that have a high immunity move slower than those with low immunity. So, if you're a resistant garter who can supplement your diet with newts, you have to sacrifice speed (probably because newts toxin is a type of neurotoxin similar to that of the puffer fish) to do so, thus the snake with a tummy full of newts is less likely to evade a hungry heron!