Insects such as mosquitoes and flies carry diseases by biting an infected host, then biting you. West Nile virus has been an issue for years, and now the new Zika virus is spreading through Florida and other states thanks to infected mosquitoes. Rats also carry diseases such as rabies as do opossums.
Pests such as moles and groundhogs dig holes in your pasture and either eat the beneficial bugs in the dirt or cause holes that can break the legs of livestock. Bugs eat your leaves and birds eat your berries and cherries. That’s just not acceptable after all of your hard work!
All of these issues can be serious now. But if SHTF, these critters can each be lethal in their own way. And so are the bigger predators that attack your crops.