The monarch butterfly is native to North, Central, and northern South America and has been accidentally introduced to numerous islands in the Pacific and Atlantic. In spring and summer, it lives in open fields with milkweed, and in fall it seeks forested areas with a specific microclimate, with overnight temperatures above freezing but cool daytime conditions. Monarch butterfly larva feed only on milkweed, while adults gather nectar from flowers and water, and because most milkweeds contain bad-tasting chemicals called glycosides that are incorporated into the adult, monarchs are distasteful to predators. Monarchs first mate when they are three to eight days old, pairs may remain together for up to 16 hours, both sexes mate several times during their lives, and females prefer to lay eggs on young milkweed plants, most often on the underside of a leaf, scattering eggs over many plants to increase the chance that some offspring survive. The egg hatches in three to four days, the young caterpillar eats its own eggshell as its first meal, and the larva then devours milkweed leaves. As it grows, the caterpillar molts four times and passes through five instars, with the body growing during each instar while the head size stays constant, and after about two weeks it reaches approximately two inches in length. The fully grown larva then seeks a place to begin pupation, attaching itself under a leaf or over an overhang with hooks in the last pair of legs to a silken pad, forming a pre-pupal j, shedding its skin for the last time, and revealing the pupa, whose cremaster hooks into the silk pad as the larval skin is shed. The chrysalis stage lasts about two weeks, the mature butterfly becomes visible through the pupal cuticle during the last twenty-four hours, and the fully developed butterfly performs contractions that split the covering and allow it to emerge. After emergence, it inflates its wings to full size, and within a few hours the adult begins to fly and gather nectar. The life cycle from egg to butterfly takes approximately four to five weeks, and the adult’s main function is reproduction through mating and laying eggs that become the next generation. Males have thin veins on the wings and a pronounced black spot, while females have thick veins and no black spots.