Danaus plexippus
Copyright, T. W. Davies, California Academy of Sciences
The Monarch is one of our
best-known butterflies. It is a large insect, growing up to
four inches wide. Monarchs are bright orange with black
veins and white dots. Underneath their wings, they are much
paler. You can tell males from females, because males have
thinner veins and two black spots on their hind wings. These
spots release a smell to attract females. Monarchs are usually seen
in weedy fields, meadows, marshes, roadsides, and near
water, such as streams, ponds, and lakes. Copyright, Will
Cook Dale Clark After mating, female
Monarchs lay eggs, one at a time, on certain plants. They
only lay eggs on plants in the milkweed family. These host
plants are the only food Monarch caterpillars will
eat. Caterpillars hatch from a
pale green egg and eat their own egg shell before starting
on the host plant. Caterpillars continue to eat and grow,
only leaving their host plant if they've eaten all the
leaves and need to find a new milkweed. Caterpillars grow up to
two inches long. They are white with black and yellow
stripes. The leaves of milkweed
plants are poisonous to most animals, because they contain
chemicals called "cardenolides." Monarch caterpillars are
not affected by cardenolides; in fact, they store these
chemicals inside their bodies, which makes the caterpillars
poisonous to most animals. Later, when the caterpillars turn
into adult butterflies, the cardenolides stay
inside. Very few vertebrates
(animals with backbones, such as mammals and birds) eat
Monarch caterpillars or adults, although many will give them
a try before spitting them out. From then on, the animal has
learned that Monarchs aren't good to eat and they avoid
them. Invertebrate predators
(animals without backbones, such as other insects), don't
seem to mind the cardenolides so much. Therefore, Monarchs'
main predators are insects, such as wasps, ambush bugs, and
some species of stink bugs. Spiders also eat Monarchs. It is
believed that some lizards and frogs (even though they're
vertebrates) eat them too. Mark Moran Copyright, Dale A.
McClung Copyright, Dale A.
McClung When a caterpillar has
had its fill of milkweed leaves, it looks for a place to
pupate (resting stage). The name for a butterfly pupa is a
chrysalis. A Monarch chrysalis is almost an inch long, jade
green with gold spots, and plump. The adult Monarch
butterfly will emerge from the chrysalis in a few
weeks. Adult butterflies drink
flower nectar for food. Milkweed flowers are one good source
of nectar, but these butterflies visit many other flowers
too, including: clovers, thistles, goldenrods, ironweed, and
sunflowers. Monarchs are also
interesting, because they are one of the few butterflies
that migrate. In early Fall, all of the
Monarchs in our area form large groups and head South. They
travel over 2000 miles to Mexico, where they will spend the
winter. These butterflies will not make it back North.
Instead, they mate, lay eggs, and die in Mexico. The Monarch eggs laid in
Mexcio hatch into caterpillars, which then pupate and become
new Monarchs. In the spring, the young Monarchs begin flying
North. These Monarchs won't make it to our area either, but
they will mate and lay eggs along the way. It is the next
generation of butterflies that makes it to us. Mark Moran
Mark Moran
Some Monarchs live for
months, and some only live for a few weeks. The butterflies
that migrate South in the fall live the longest, up to eight
months. Monarchs born here in early Summer only live a month
or so, since they do not have to make a journey. Monarchs are used as
hosts by certain parasites, including tachnid flies and
braconid wasps. Monarchs also help some
other species of butterflies. Some orange-colored
butterflies, especially the Viceroy, are mimics of Monarchs.
This means, even though Viceroys aren't poisonous, predators
avoid them, thinking they are Monarchs. Viceroys gain
protection just by looking like a Monarch. Copyright, Will
Cook
