Butterfly Life Cycle: Egg
Excerpted from: Facts About Butterfly Eggs
Butterflies may be small-winged insects, but butterflies are among the world’s most interesting members of the
animal kingdom.
Butterflies are found everywhere in the world and contain thousands of different species, with
750 species found in the United States. Their sizes vary from less than half an inch long, to some species
that can reach up to 10 inches long between wing tips. We may know much about their size, color and habitats
but lesser is known about butterfly eggs.
Butterfly Eggs — Just The Facts
Eggs are usually laid on tender young leaves or buds
Eggs are attached to a leaf using an adhesive-like substance that glues the egg to the plant leaf
Each egg is surrounded by a chorion, a hard outer shell that protects the larva
Small funnel-shaped openings called micropiles are on top of each egg where water and air enter
Butterflies lay an average of between 100 to 300 eggs
The butterfly's eggs usually hatches after 3 to 8 days
Painted Lady
Butterfly Egg
Butterflies grow through a four-stage process known as complete metamorphosis, changing from egg to
larva to pupa and finally to adult. The eggs hatch into a larva, which we know commonly as a caterpillar.
The caterpillar then grows by molting its outer exoskeleton. Larvae can do this a few or several times
before they enter into the next phase of development — the pupa.
The pupal stage, known as a chrysalis in
butterflies, the insect is typically non-mobile and appears to be resting. During this stage the pupa is
changing drastically, forming the often colorful, scaly wings that butterflies exhibit. Once the mature adult
emerges from the pupa, it is ready to find a mate for producing offspring.
The larvae of most species will only eat the leaves of one or two species of plant and will die if they find
themselves on the wrong type of tree, bush or herb. Even oligophagous species, those that are able
to feed on more than one type of plant, have a hierarchal order of food plant preference, only accepting
less nutritional species if they are unable to locate their preferred food plant.
It isn't just enough to locate the correct species of plants, the eggs usually have to be laid on tender
young leaves or buds, as the older leaves often contain toxins that can kill them.
Monarch Butterfly Eggs
Butterflies therefore spend a great deal of time checking various leaves to ascertain whether they are
of the correct species for egg-laying.
Studies have shown that butterflies initially determine leaf choice
by shape and size, but use taste and smell to confirm that the leaf is chemically 'correct'.
It is common to see butterflies flitting from plant to plant, alighting momentarily on leaves, tasting
the foliage using olfactory sensors on their feet. All female butterflies have spines on the underside
of their forelegs. When they land on a leaf these spines puncture the surface, releasing aromas that
are detected by the olfactory sensors.
It isn't just enough to locate the correct species of plant. The eggs usually have to be laid on tender
young leaves or buds, as the older leaves often contain toxins that can kill them.
They also have to be laid on plants that are growing in very precise conditions — just the right degree
of shade, just the right conditions of temperature and humidity, and at a height on the plants where they
will not get eaten by browsing herbivores.
Eggs are often laid on the tips of buds, usually quite high up on the tree or bush.
This way they are less likely to be found by ants. Female butterflies often spend long periods probing
about with the tips of their abdomens, being extremely careful about the positioning of each individual
egg.
To protect the egg and embryo that is forming, the eggs are attached to a leaf by the butterfly using an
adhesive-like substance that glues the egg to the plant leaf. The nature of the 'glue' is still fairly unknown
in the scientific community. This glue holds the eggs to the leaf in such a way that they cannot be
separated without destroying the eggs.
Small funnel-shaped openings called micropiles can be found
on top of each egg. This is where water and air enter while the egg is developing. Each egg is surrounded
by a chorion, a hard outer shell that protects the larva. Some shells have raised ribs.
Question Mark
Butterfly Eggs
Butterflies are oviparous, meaning they lay eggs. Eggs from the female
butterfly are fertilized by sperm from the male. The female butterfly stores the male’s sperm in a bursa, or sac,
until she is ready to lay eggs.
Depending on the species, females lay eggs one at a time, in clusters, or in
batches of hundreds. Butterflies lay an average of between 100 to 300 eggs, although some species may
only lay a few dozen, others can lay as many as a 1,000 or more.
The butterfly egg is spherical or ovate shaped, varying in color and size. It is covered by chorion, a hard
shell that protects the egg, and is lined with a waxy layer that prevents dehydration. It is full of nutrients
and is commonly the he newly hatched larva. There is a small opening called a 'micropyle' which allows
sperm to enter the egg for fertilization while inside the female.
Butterfly eggs vary in size from about 1 to 3 mm in diameter. The eggs can be smooth or textured, their
shapes can be oval or round and their colors can be yellow, white, green or other shades, depending
on the species.
The Zebra Longwing butterfly, for instance, produces eggs that
look like tiny cobs of corn while the eastern Black Swallowtail butterfly
produces smooth, pale-green, globe-shaped eggs.
The egg shell also is peppered with thousands of microscopic pores called aeropyles.
Examination of the eggs reveals them to be adorned with hundreds of minute hexagonal pits. Tiny hollow
spines emerge at the intersections of each hexagon. These are also aeropyles, and act as breathing
tubes for the developing larva.
Orange Tip Butterfly
Emerges From Egg
A female butterfly lays a great number of eggs. They also take special care of their eggs. The eggs need to
be kept warm and must have the appropriate moisture or they will either rot or dry out. A big portion of
these eggs will not hatch to become butterflies as they are vulnerable to many predators such as birds,
spiders, other insects and small mammals. Of the few hundred butterfly eggs laid, very few will reach
adulthood.
Inside each egg, a yolk can be found that serves as nourishment for the developing larva. A butterfly egg
hatches after 3 to 8 days depending on temperature and season of the year. A change in the egg’s
color before hatching is normally visible. After hatching, some caterpillars eat their own eggshells as their
first meal but most of them eat parts of the plant that the eggs were laid on.
The average time for the embryo to develop is 7-14 days but in instances where the egg is the overwintering stage,
the embryo may take months to develop.
The eggs of butterflies and moths are valuable sources of protein. In addition to the threats from birds,
snails, reptiles, amphibians and grazing mammals already mentioned, they are prone to parasitization by
microscopic wasps and flies. It may seem surprising that something as small as a butterfly egg has its
own parasites, but these cause high losses. The main parasites are wasps — as many as 60 of these can
emerge from a single butterfly egg!
Vocabulary |
Aeropyle |
Aeropyles are microscopic holes that dot the surface of the egg. Aeropyles let oxygen
into the egg. |
Bursa |
Opening allowing copulation by the male butterfly and entry of sperm into the copulatory
bursa. |
Chorion |
Each butterfly egg is surrounded by a hard outer shell, called the chorion, to protect
the developing larva. |
Chrysalis |
The transformation stage between the larva and the adult. |
Exoskeleton |
A butterfly's skeleton is not inside their body, but on the outside and is called the
exoskeleton. It's like having skin made of bones. |
Micropyle |
Each egg contains a number of tiny funnel-shaped openings at one end, called micropyles. |
Oligophagous |
Feeding upon a limited variety of food, as certain caterpillars whose diet is restricted to
a few related plants. |
Butterflies and Moths of North America
WisconsinButterflies.org
Southern Wisconsin Butterfly Assn (NABA)
The Butterfly Site