The primary job of the adult stage is to reproduce—to mate and lay the eggs that will become the next generation. Monarchs do not mate until they are three to eight days old. When they mate they remain together from one afternoon until early the next morning—often up to 16 hours! Females begin laying eggs immediately after their first mating, and both sexes can mate several times during their lives. Adults in summer generations live from two to five weeks.
Each year, the final generation of monarchs, adults that emerge in late summer and early fall, has an additional job. They migrate to overwintering grounds, either in central Mexico for eastern monarchs or in California for western monarchs. Here they spend the winter clustered in trees until weather and temperature conditions allow them to return to their breeding grounds. These adults can live up to nine months.
Male and female monarchs can be distinguished easily. Males have a black spot on a vein on each hind wing that is not present on the female. These spots are made of specialized scales which produce a chemical used during courtship in many species of butterflies and moths, although such a chemical does not seem to be important in monarch courtship. The ends of the abdomens are also shaped differently in males and females, and females often look darker than males and have wider veins on their wings.
1) Male monarch abdomen 2) Female monarch abdomen
3) Female monarch wings 4) Male monarch wings
The body of an adult butterfly is divided into the same major parts as the larva: head, thorax, and abdomen. There are four main structures on the adult head: eyes,antennae, palpi, and proboscis. A butterfly’s relatively enormous compound eyes are made up of thousands of ommatidia, each of which senses light and images. The two antennae and the two palpi, which are densely covered with scales, sense molecules in the air and gives butterflies a sense of smell. The straw-like proboscis is the butterfly’s tongue, through which it sucks nectar and water for nourishment. When not in use, the butterfly curls up its proboscis.
1) Adult monarch compound eyes, 2) Adult monarch tarsus (Photos: Michelle Solensky)
3) Adult monarch proboscis (Photo: Sonia Altizer), 4) Adult monarch wings scales (Photo: Michelle Solensky)
The thorax is made up of three segments, each of which has a pair of legs attached to it. The second and third segments also have a pair of wings attached to them. The legs end in tarsi (singular, tarsus), which grip vegetation and flowers when the butterfly lands on a plant. Organs on the back of the tarsi "taste" sweet liquids. Monarchs and other nymphalid butterflies look like they only have four legs because the two front legs are tiny and curl up next to the thorax.
1) Monarch aposematic coloration 2) Monarch nectaring 3) Monarch on Aster