Venom Denaturing with Heat
Regarding snake venoms, they tested 28 snake venoms at 100'C: 19/28 of the venoms were still very dangerous after 5 minutes at 100'C.

"Heating all venoms led to the denaturation and loss of some proteins; however, most of the venoms retained a significant number of proteins. Seventeen venoms contained more than seven proteins after heating, whereas five venoms contained only one to three proteins. All but nine of the heated venoms had substantial hemorrhagic activity, and Agkistrodon piscivorus piscivorus venom had very high activity, almost four times that of the second most hemorrhagic venom from Crotalus viridis lutosus."

There is a good chance that land animals have higher heat tolerance spiders and snakes can experience a lot higher heat than marine organisms. 

study of marine venoms and hot water says:
Sting ray venom is especially fast to denaturize in heat, and most fish spine venoms are. HWI hot wat immersion is recommended for fish spine stings by some organizations. They did tests to find that box jellyfish, sting rays and other sea creatures stings react significantly to HWI. 

They tested that 122/138 marine envenomations were improved by HWI from a variety of surveys. 

there are 50,000 marine stings a year from 2000 species and 
about 5 million snake bites, 2mn envonomings and 20-125,000 deaths by snakes every year from 400 species out of 3000 species of snakes which are dangerous to humans. 

Dangerous snake and spider bites are generally treated in hospital, and the only wise thing to do is not to not make your blood go around your body very fast by being active after a bite, stay calm and alert.