The Milkweed Butterflies
- The family is known
as the Milkweed butterflies because the caterpillars of most of its members
feed on some variety of milkweed (Family Asclepiadaceae). When feeding
on these plants, the caterpillars obtain certain chemicals which remain in
their bodies. The chemicals cause them to be distasteful to predators,
both as caterpillars and later as adults, and through experience, potential
predators learn to avoid these species.
- Some authors consider
this group of butterflies to be a subfamily of the Nymphalidae, the Brush-footed
butterflies, because the Danaidae, like the Nymphalidae, have forelegs that
are reduced in size. However, unlike the Nymphalidae and most of the
other butterflies in our region, the Danaidae are unique in that their antennae
are not covered with scales.
- Most members of this
family occur in Asia; only four species occur in North America, one of which
is the well-known Monarch. Two species occur in Idaho, and both belong
to the Subfamily Danainae.
- In additon to the traits
described above, this family is also characterized by: 1) large size, with
a wingspan typically of three inches or more; 2) orange, brown, or black coloration
in North American species; and 3) a hair
pencil, a brushy
extension from the rear of the abdomen in males, which is used to direct pheromones
towards a female during courship.
- Eggs are typically elongated
and ribbed. Caterpillars are typically brightly colored and without
hair or spines but
bearing a pair of long filaments
at each end. Pupae form no cocoon,
have a cremaster
but no silk girdle,
and may be spotted.
Danaus plexippus- Monarch