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Whereas bright colors in flowers and fruits are generally designed to attract pollinators or potential seed dispersers, bright insects or amphibians often signal toxicity or venom. Isn't it interesting that birds that are not renowned for their intellect are able to discriminate among these conflicting signals? In other words they will eat a red fruit but avoid a red insect. Here are a few examples of such warning colors in animals that I have come across recently.
Many caterpillars are defended by spines and toxicity such as this Baltimore checkerspot. In most cases the toxicity is due to compounds derived from plant food. This is also the case for the milkweed bug, the elderberry borer beetle, and the juvenile giant sweet potato bug (found feeding on deadly nightshade). The evolutionary processes by which insects developed means of overcoming plant toxicity and then using this plant defense as part of their own protection are fascinating. The metallic green tiger beetle is an exception in that it is a predator and the purpose of its bright color is unknown.
Possibly an energetically cheaper means of defense is mimicking another species that is toxic by adopting its color and pattern. The spicebush swallowtail is one of a group of butterfly species that resemble the toxic pipevine swallowtail that derives its protection from eating pipevine as a caterpillar. Several kinds of salamander (such as the northern red found in our VA yard) mimic the toxic land phase of the spotted newt, the red eft, and thus gain protection from predators. The eft has tetrodotoxin in its tissues which is a very potent neurotoxin similar to that found in the deadly puffer fish (which amazingly is eaten by some Japanese as fugu). Tetrodotoxin is the most toxic non-protein substance known and acts by blocking the membrane channels by which sodium enters nerves, thus stopping nerve transmission to muscles. It is unclear at present whether this remarkable and most efficient toxin is produced by the amphibian or symbiotic microorganisms.
What can we learn from the astonishing adaptations of animals to protect themselves with poisons, and to advertise this danger to potential predators? Obviously be careful what you touch and be aware of how the poisons are transmitted. I have often picked up red efts without any problem. But do not put them in your mouth as fraternity boys have done at some college campuses! Another lesson that can be learned from toxic insects is to avoid the toxic plants they are consuming. For example I first realized that dog fennel was toxic by observing that the toxic salt marsh caterpillar feeds on this plant, which is sometimes recommended as a flavoring in cooking. Just remember that "natural" substances can be incredibly toxic; it is a jungle out there where the survival of the fittest requires great care if you choose to eat wild foods.
Bill Dunson Englewood, FL, and Galax, VA