About Russia I am not really informed but I guess Wolves and bears are probably the most dangerous animals you can find there. As for Mexico, there are some dangerous insects and snakes. In Mexico city it is hard to find dangerous animals. The most dangerous you can find here are tarantulas and scorpions (dark scorpions, that are actually not as dangerous as the yellow scorpions). In other states you can find yellow scorpions, black widows (their poison is more powerful than the poison of a cobra), rattlesnakes.