Adult
Egg | Larva/Caterpillar | Pupa | Adult
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, (which emerges 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 survive the long winter until conditions which allow
them to return to their breeding grounds. These adults can live up to eight
or nine months.
Male
and female monarchs can be distinguished easily. Males have a black spot
(indicated by red arrow in image above) 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.
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 (see image below), 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.
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.
