LITTLE THINGS

during the four years i spent as caretaker at canelo hills cienega, a nature conservancy preserve in southern arizona, one of the many natural events that marked the cycle of seasons was the arrival of monarch butterflies, which lay their eggs on milkweed plants. monarchs are famous for their astonishing transcontinental migrations -- those living east of the rocky mountains fly to central mexico. their milkweed diet provides monarchs with a foul taste, an effective defense when coupled with the distinctive colors and markings which advertise their toxicity to would-be predators.

monarchs can be confused with viceroy butterflies, a non-toxic species whose coloration resembles that of the monarch, thereby benefitting since predators avoid both. this apparent mimicry, or aposematism, is a fairly common natural event. over the course of evolutionary generations, a trait is accidentally introduced by genetic variation during reproduction. if that trait confers a survival or reproductive advantage (in this case, visually resembling a toxic species), the organism survives to reproduce, and the gene is passed to succeeding generations, eventually spreading throught the non-toxic species until the trait becomes a defining feature.