One of the dumbest pieces of bad advice I’ve ever heard anyone give in the context of wilderness foraging is: “Watch what the animals eat… If they can eat it, so can you”. That is no way, I repeat NO WAY to determine whether a wild plant is edible or not.
Animals have different physiologies than humans and what may be harmless to a deer, bird or other woodland creatures may be a deadly poison to humans.
“Deer eat strawberry bush twigs, and birds eat the fruits, but both parts are deadly to humans, causing vomiting, diarrhea, irregular hearbeats, convulsions, coma, and death. Scientists don’t know what type of poison it is. Strawberry bush is also poisonous to livestock. It was advantageous for deer to evolve the ability to digest a plant that was likely poisonous to competing herbivores of the Pleistocene, such as bison and horses.
Buffalo nut is toxic to humans, rabbits, and pigs, but not deer, cattle, horses, sheep, and mice. Its poison is an amino acid similar to that found in cobra poison. The protein stimulates growth hormone in deer and may facilitate antler growth.”
While there are far more plants in the wild that are safe to eat than poisonous ones, the only failsafe way to be sure which wild plants are edible is to educate yourself on the native plant life in your area. There are many books available that will teach you how to identify wild plants that are safe to eat. You should also learn how to test plants if you’re not sure. This takes a bit of time, though, and involves first tearing off a piece of the plant and testing it on your skin for a reaction. If there’s no skin reaction after 8 hours, rub some of the plant on your lip. If there’s no tingling, numbness or reaction after 8 hours, put a small piece in your mouth. If still nothing happens after 8 hours, try swallowing a small bit of it. If that doesn’t make you sick or give you the runs, try eating a little more, etc.
However, this is no substitute for KNOWING. For example; if you can’t visually identify poison ivy, oak or sumac, you don’t want to go rubbing it on your skin to find out if you should eat it or not.
Also, in a survival situation, dehydration is a major risk and you should avoid ingesting anything that will make you vomit or give you diarrhea. But if you’re not sure, or you find yourself in an area where you’re unfamiliar with the local vegetation, it’s good to know how to test a plant before eating it.
While I’m on the subject of the foolishness of taking cues from the animals to determine what’s safe to ingest; the same goes for water… Just because you see an animal drinking from a natural water source, that doesn’t mean it’s safe to drink untreated. That’s like saying it’s safe to drink water from the toilet because your dog can.
No matter how clean or clear the water LOOKS, there are microscopic buggers in there that you can’t see, which don’t bother the critters none, but will put you in a world of hurt. In the wild, water should ALWAYS be filtered AND sanitized before drinking.
For further reading, here’s an interesting article I came across from a blog called: Georgia Before People.