One of the dumbest examples of wilderness survival folklore ever espoused is the notion that to determine whether a potentially edible plant is poisonous or not, a person should observe an animal consuming the plant. The logical fallacy is the assumption that if the animal could eat the plant and not die, than it would be safe for humans to eat. This is a stupid assumption for 2 reasons: First, the animal could crawl off in the bushes and die later out of sight. Second, and more importantly, all animals have completely different physiologies than humans. There are many plants highly poisonous to humans but perfectly edible to many species of mammals, birds, and especially insects, such as caterpillars which consume poisonous plants that make them inedible to birds when the caterpillars become butterflies. Below are 2 species of common plants found in Georgia that are favorite foods of deer but are poisonous to humans.
Strawberry bush–Euonymous americanus. Naturalist refer to the plant as “ice cream” for deer. But it is poisonous to humans. It’s in the bittersweet family.
Buffalo nut–Pyrularia pubera. Also a favored deer edible that is poisonous to humans. It’s in the sandalwood family.
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. I wonder if other browsing Pleistocene herbivores (mastodons, tapirs, Jefferson’s ground sloths) could also eat strawberry bush without ill effect. Browsers tend to be more resistant to plant poisons because they eat small amounts of a great variety of foods and don’t concentrate the poison in their systems. Grazers eat large quantities of fewer species of plants, making it more difficult to evolve the ability to eat toxic vegetation. Deer probably evolved the capacity to survive eating toxic plants because they only nibbled on the plant, and individuals that could survive eating small quantities passed this characteristic on to the next generation, unlike bison which ate such large quantities that no individuals survived consuming the toxins. Gradually, each generation of deer had a growing inherited capacity to digest this toxic plant with no ill effects.
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. In addition to harboring plant toxins, buffalo nut is a parasite, living on nutrients from other tree’s roots. The roots of a buffalo nut “kiss” the roots of other species forming a hausteum, an attachment that helps them leech nutrients absorbed by the other tree. Many species of trees serve as host species for buffalo nut, including oak, chestnut, and hemlock.
Both strawberry bush and buffalo nut grow as understory trees in disturbed moist woodlands–a habitat that expanded during interstadials and interglacials but decreased during stadials. Grazers always became more abundant during stadials when arid cool climates fostered the growth of grasslands but decreased the abundance of toxic woodland plants. Browsers increased when forests expanded. Strawberry bush and buffalo nut are known as “gap phase” species, thriving in areas of the forest disturbed by fire, storm, or human activity.
Like most plants, strawberry bush and buffalo nut are invisible in the Pleistocene fossil record, but they must have been present then or they wouldn’t be here today.
Speaking of (or rather writing of) ice cream for deer, I tried growing fava beans in my garden 2 years ago. Fava beans are a cold hardy legume. I read they could survive temperatures as low as 15 degrees F. Because winters in Augusta, Georgia seldom get that cold, I predicted they would do well. I had a great stand of fava beans in my backyard by early December. One afternoon while taking a walk in broad daylight, I saw a deer. It stopped about 20 yards from where I stood. It seemed unafraid and even stomped its hooves as if attempting to intimidate me. I resumed walking up the street until I heard hooves hitting pavement behind me. I realized it was heading straight for my fava bean patch. I raced back to scare it away but 2 big dogs came out of nowhere and chased the fleeing deer from my garden for me. My fava beans were safe but nor for long–a few days later the temperature dropped below 15 degrees, an unfortunate stroke of luck because temps here get that cold maybe once every 10 years. The favas did sprout back from the roots but production was meager compared to what would have been from the lush first growth.