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Butterflies reproduce by laying eggs, typically on
leaves of plants. The number of eggs lain by a butterfly
at one time varies between species. Butterfly eggs
are protected by a hard and often ridged outer layer
of shell, called the chorion. Butterfly eggshells
are each lined with a thin coating of wax, which prevents
the egg from drying out before the larva can finish
developing. The surface of each egg features several
small, funnel-shaped openings at one end, called micropyles,
the purpose of which is to allow sperm to enter and
fertilize the egg. Butterfly eggs vary significantly
in size between species, and may also vary in texture
and colour. However, all butterfly eggs are either
spherical, cylindrical, or oval in shape.
For most species, developing larvae remain in eggs
for a few weeks. However, eggs lain shortly before
winter, especially in temperate regions, undergo a
resting stage before the eggs finally hatch in the
spring. Other butterflies may lay their eggs, which
will not hatch until the summer, in the spring. Though
most butterfly eggs are lain on plants, each species
of butterfly has its own range of host plants. Some
species of butterfly are confined to only one species
of plant, while others use a range of plant species.
The latter species of butterflies, however, still
tend to be more or less confined to host plants of
a certain family.
Butterfly eggs are fixed to the leaf on which they
are lain with a glue-like substance that the mother
butterfly secretes. This "glue" hardens rapidly, contracting
as it does so and deforming the shape of the egg.
This glue forms a meniscus, and is conspicuously visible
on the base of every butterfly egg. This material
is not only used to adhere eggs to the leaf on which
they are lain; butterflies also use this material
while forming a chrysalis. The glue is produced by
a pupa to secure the setae of the cremaster, the small
hook-like structure that connects the chrysalis to
the branch that supports it. This glue becomes so
hard that the silk pad to which the setae are glued
cannot be separated from the setae. As the nature
of the glue is unknown, it is a proper subject for
potential research.
Butterfly larvae, or caterpillars, bite their way
out of their eggs in order to hatch. Immediately after
hatching, caterpillars continue to eat the eggshell
from which they came, and begin eating the leaf to
which it was attached; from the time that they are
hatched, caterpillars spend the vast majority of the
duration of the larva stage in search of food. Many
species are even considered pests among farmers because
of their voracious eating. Most caterpillars subsist
on a diet of only plant leaves. However, some species
eat insects; these include Spalgis epius and Liphyra
brassolis, which both belong to the lycaenids family.
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