A common misconception is anything "natural" is healthy and beneficial.
Nothing could be further from the truth!
The dominance of humans on planet Earth is primarily linked to cultivation and domestication of a small number of plants and many of the rest are toxic.
Milkweed tussock moth caterpillars are covered with hairs and bristles to discourage predators.
In some tropical environments humans only exist in primitive circumstances by figuring out how to remove the toxins from starchy plants (manioc and sago palm, for example).
It has even been suggested that the evolution of the human brain came about because early plant-eating primates required a complex brain to remember what to eat when, and some plants countered with mind-altering chemicals that interfered with such thought.
Examples of the continued evolutionary arms race between predator and prey and herbivores and their food plants ensue.
William Dunson, Ph.d., professor emeritus of biology at Penn State University, splits time between Southwest Florida and his farm in Galax, Va. He can be reached at firstname.lastname@example.org.
In mid-summer, pastures are often covered with an exotic but beautiful blue flower: chicory. Cattle do not eat it so it thrives in pastures and on the sides of roads where it has less competition with grasses.
A similar situation occurs with the spectacular but apparently toxic cardinal flower, which thrives only in disturbed waterside habitats or in wet meadow pastures where competition with grasses is reduced by horse and cattle grazing.
Many animals reduce their chances of being eaten by using camouflage.
The katydid is an astonishing mimic of green leaves; it even has leaf vein-like structures indicating how there has been selection for color and fine leaf-like structure.
Similarly a moth caterpillar on ironweed is a mimic of brown leaves and twigs. When discovered it rears up and assumed a threatening pose; it was also hard to tell the head from the tail. Bird predators carefully examine plants for insect food and only the best mimics survive to pass on adaptive traits to their progeny.
Some toxic insects advertise their distastefulness to potential predators. Monarchs and their brightly colored toxic caterpillars derive their protection from chemicals in their food plant.
Another of the milkweed-dependent group of insects is the milkweed tussock moth; the caterpillars are brightly colored and covered with hairs and bristles to discourage predators with their food-derived toxicity.
Advertisement of toxicity is somewhat less common in vertebrates but red salamanders are famous for their bright red color, which warns of toxic mucus, and in their mimic resemblance to the even more toxic red eft stage of the newt.
Probably the most interesting and surprising strategy used by some insects is the bluff or "scary eyes" tactic. The common buckeye butterflies fly slowly and stop often to bask.
They are not protected by toxins so how do they deter predators?
Are birds really afraid of these tiny but distinctive eye marks?
Or is the purpose of the eye spots to direct attacks to the spots rather than the vulnerable head and body of the butterfly?
An older buckeye does not show large bird peck marks on the wings, just some fraying edges. Insects using eye spots show predators (especially birds) are quite alert to anything unusual about prey that might indicate poison or the ability to fight back. This apparently led to the evolution of "eye spots."