Butterfly eggs come in many shapes and colors. The shapes include spherical, oval, and pod-shaped; the colors include white, green, and yellow.
The eggs have a thin, tough, protective shell, the chorion. This shell has raised ribs or pits (reticulations).
At the top of each egg is a micropyle, a small pit that marks where the sperm enters the egg. While the egg is developing, air and water also enter the egg through the micropyle. In addition, aeropyles (microscopic holes that dot the surface of the egg) let oxygen into the egg.
There is a yolk inside each egg that nourishes the developing larva. When it is time to hatch, the larve gnaws open the egg shell with its jaws. After hatching, most caterpillars finish eating their egg case as their first meal. After this, the plant upon which the egg was laid is usually the larva's
Caterpillar Anatomy
Caterpillar Printout
caterpillarA caterpillar is the larval stage of butterflies and moths. This stage usually lasts from about two weeks to a month, and is the longest life stage for many lepidoptera (butterflies and moths). During this stage, the caterpillar can grow in size more than 30,000 times.
Caterpillars have a segmented body consisting of a head, a thorax (with three pairs of jointed legs with hooks), and an abdomen (usually with five pairs of stumpy prolegs). Its primary function is to eat and grow in preparation for pupating.
Eating, Tasting, and Smelling
caterpillar head The caterpillar will spend most of its time eating, and has powerful jaws that will serve this purpose. These well-developed jaws (mandibles) have very sharp cutting surfaces that easily chop leaves. The mandibles bite off plant material and tear it into small, easily digestible pieces. Underneath the mandible are the two maxillae, smaller mouth parts that guide the food into the mouth. The caterpillar holds onto the food with its thoracic legs.
The maxillae also have taste cells; these chemical detectors tell the caterpillar to eat when the food is appropriate, and not to eat when the food is not appropriate. The tiny antennae, which are near the mouth parts, sense smells.
Caterpillars are very limited in their diet; many species will only eat the leaves of a single type of plant.
Digestion
Most of a caterpillar's body is filled with intestines that quickly digest its food. Since the caterpillar is growing amazingly quickly and must also store enough food energy to fuel its pupal stage, digestion nourishment is a primary function.
Cells, Growth, and Imaginal Discs
Usually when organisms grow and develop, the number of cells in their body increases. This is NOT so with caterpillars. The newly hatched larva has the same number of cells as the large caterpillar which is ready to pupate.
For the most part, the cells that comprise the caterpillar are not the cells that will become the adult (butterfly or moth). The caterpillar has imaginal discs within its body. Different clusters of these cells will develop into different adult body parts. For example, one cluster will develop into the adult's compound eyes.
Molting and Instars
As caterpillars grow, their exoskeleton becomes tight on them, so they molt (lose their old exoskeleton). Ecdysone is the molting hormone of insects. It causes an insect to molt.
After the molt, while the new skin is still soft, they swallow a lot of air, which expands their body. Then, when the cuticle hardens, they let the air out and have room for growth. Caterpillars molt four or five times as they grow. Each different caterpillar stage is called an instar.
Coloration
Monarch larva
The Monarch caterpillar is brightly colored and is poisonous.
Caterpillars come in many colors and patterns. Many caterpillars are camouflaged to blend into their surroundings (the host plant), thus hiding them from predators. Generally, the brightly colored larva are poisonous; their color is a reminder to predators about their toxicity.
Protection from predators
Caterpillars are soft bodied and slow moving. This makes them easy prey for predators, like birds, wasps, and mammals to mention just a few. Some caterpillars are even eaten by their fellow caterpillars (like Zebra swallowtail larva which are cannibalistic).
In order to protect themselves from predators, caterpillars use different strategies, including:
* Poison Some caterpillars are poisonous to predators. These caterpillars get their toxicity from the plants they eat. Generally, the brightly colored larva are poisonous; their color is a reminder to predators about their toxicity. Some poisonous caterpillars include the Monarch and the Pipevine Swallowtail.
* Camouflage Some caterpillars blend into their surroundings extraordinarily well. Many are a shade of green that matches their host plant. Others look inedible objects, like bird droppings (the young Tiger Swallowtail larva).
*
tiger swallowtail larva
The Tiger Swallowtail caterpillar has large eyespots.
Eyespots Some caterpillars have eyespots that make them look like a bigger, more dangerous animal, like a snake. An eye spot is a circular, eye-like marking found on the body of some caterpillars. These eyespots make the insect look like the face of a much larger animal and may scare away some predators.
* Hiding Some caterpillars encase themselves in a folded leaf or other hiding place.
* Bad smells Some caterpillars can emit very bad smells to ward off predators. They have an osmeterium, an orange, y-shaped gland on their neck which gives off a strong, unpleasant odor when the caterpillar is threatened. This keeps away dangerous wasps and flies that try to lay eggs in the caterpillar. Many swallowtails have an osmeterium, including the Zebra Swallowtail.
Legs
Caterpillars have two types of legs which perform different functions.
* Thoracic legs: Caterpillars have three pairs of jointed legs with hooks; these are attached to their thorax. Caterpillar's thoracic legs hold onto its food.
* Prolegs: The prolegs are stumpy legs that let the caterpillar climb very well, even up vertical surfaces. Caterpillars usually have five pairs of stumpy prolegs on the abdomen. These prolegs have crochets (small grasping hooks) on them. The last pair of prolegs are called anal prolegs; they are at the very end of a caterpillar's abdomen (hind region). These prolegs disappear in the adult.
Locomotion
A caterpillar moves in a rippling fashion. It contracts the muscles in its rear segments, pushing blood into the forward segments, which lengthens the front part of the body. The legs hold onto the forward position and then the front muscles contract, pulling the rear segment forward.
Breathing
Spiracles are an insect's breathing pores. They are usually located on the thorax and abdomen.
Sight
Caterpillars have six pairs of simple eyes (ocelli). Ocelli (also called stemmata) are small, simple eyes that can detect changes in light intensity, but cannot form an image. Ocelli are composed of photoreceptors (light-sensitive cells) and pigments. Ocelli are usually located in two clusters of six eyes on the sides of a larva's head.
Sense of Touch
Caterpillars sense touch through tiny hairs (setae) that are all over the caterpillar's body. These tactile hairs grow through holes in the pinaculum (dark, flattened plates on a caterpillar's body) of the exoskeleton. These hairs are attached to nerve cells, and relay information about touch to the insect's brain.
A chalaza (pl. chalazae) is a raised sclerotized (hardened by scleroproteins) portion of the cuticle of a caterpillar that bears one to four setae (tactile hairs); each seta arises from a separate raised area.
The tentacles are also sense touch.
Silk Production
A spinneret is a tube-like structure on a larva's lower lip (labium) that contains the spinning apparatus (the silk glands) of the larva. The caterpillar draws silk (which is made in the salivary glands) from a tube in the spinneret. The silk dries when exposed to the air. Caterpillars use this silk to support themselves and to make webs and cocoons
Life Span
Most caterpillars live from about two weeks to a month. For many lepidoptera, this is the longest part of the life cycle.
PUPA ANATOMY
pupa The pupa is the stage in a butterfly's (or moth's) life when it is encased in a chrysalis and undergoing metamorphosis. Wings develop during this stage.
About a day before the adult butterfly emerges, the chrysalis becomes transparent.
The pupa of the Zebra Swallowtail butterfly attached to a branch.
A cremaster is a support hook (or a cluster of small hooks) at the abdominal (hind) end of a pupa. Some butterflies (like the Monarch butterfly) are supported by only the cremaster; others, like the Zebra Swallowtail butterfly attach to the support with the cremaster and bands of silk (called the girdle) around the mid-section.
The Head
Butterfly headThe butterfly's head is the location of its feeding and sensory structures. The almost spherical head contains its brain, two compound eyes, its proboscis, pharynx (the start of the digestive system), the point of attachment of its two antennae, Johnston's organ, mustache-like sensory palps, etc.
Butterflies have no jaws; they sip liquid food through the proboscis, which uncoils for feeding. The proboscis is a a tube-like, flexible "tongue" that butterflies and moths use to sip their liquid food (usually flower nectar or the liquid from rotting fruits). The proboscis uncoils to sip food, and coils up again into a spiral when not in use. The lepidopteran with the longest proboscis is the hawk moth.
Compound eyes are made up of many hexagonal lens/corneas which focus light from each part of the insect's field of view onto a rhabdome (the equivalent of our retina). An optic nerve then carries this information to the insect's brain. Butterflies and moths see very differently from us; they can see ultraviolet rays (which are invisible to us).
Antennae (singular antenna) are sensory appendages attached to the head of butterflies and moths. Antennae are used for the sense of smell and balance. Butterflies have two segmented antennae with a small club at the end of each. Moths have antennae without the club. Johnston's organ is an organ located at the base of a butterfly's antennae. This organ are responsible for maintaining the butterfly's sense of balance and orientation, especially during flight.
Palps are the mustache-like scaly mouthparts of adult butterflies that are on each side of the proboscis. These palps are covered with sensory hairs and scales, and test whether something is food or not.
Butterfly Wing Anatomy
Butterfly wings A butterfly has four wings, two forewings and two hindwings. They are attached to the second and third thoracic segments (the meso- and meta-thorax). Strong muscles in the thorax move the wings up and down in a figure-eight pattern during flight.
When the fully-grown adult butterfly emerges from its pupa, its delicate wings are crinkled, wet, and uninflated. The butterfly hangs upside-down and pumps blood into the wings to inflate them. It must then wait for the wings to dry before it can fly. When the fragile wings fray or are torn, they do not repair themselves.
Butterfly veinsWing Structure and Scales: Butterfly wings are made of two chitonous layers (membranes) that are nourished and supported by tubular veins. The veins also function in oxygen exchange ("breathing"). Covering the wings are thousands of colorful scales, together with many hairs (setae). The name Lepidoptera (which includes butterflies and moths) means "scale wing" in Greek. These wing scales are tiny overlapping pieces of chitin on a butterfly or moth wing. The scales are outgrowths of the body wall and are modified, plate-like setae (hairs). The front and back of the wings usually have different patterns.
Scent scales are modified wing scales on the forewing of male butterflies and moths (on the costal fold) that release pheromones. These chemicals attract females of the same species. Scent scales are also called androconia.
WINGSPAN
Wingspan is the distance measured across a butterfly's (or moth's) wings. The butterfly with the biggest wingspan is the Queen Alexandra's Birdwing, which has a wingspan up to 1 ft (30 cm) wide.
Color: Many butterflies and moths are brilliantly colored, while others are drab. There are often ultraviolet patterns in the wings that we cannot see, but which may be seen by other butterflies. Even many of the colorful species have drab-colored outer wings (that are visible when the animal is at rest). The coloration of these insects serves many purposes, including:
* Camouflage, in which the color of the animal helps it blend into the environment, hiding the insect. The Australian leafwing butterfly, for example, is shaped and colored like a leaf.
* Warning (or aposematic) coloration: brightly-colored butterflies and moths are either bad-tasting or a mimic of similar-looking bad-tasting butterflies.
* Attracting and finding mates, who look for certain colors and patterns.
* Deceiving predators into thinking they're bigger than they really are. Some wings have large "eyespots" which make the butterfly or moth look like the face of a larger animal (like an owl), scaring away some predators.
* Soaking up heat: dark-colored scales soak up heat very well when the butterfly suns itself. Like all insects, butterflies are cold-blooded. When they get too cold, they warm themselves in the sun.
Thorax
The thorax is the locus for locomotion. The thorax is divided into three segments; on each segment is a pair of jointed legs. The four wings of the butterfly (or moth) are also attached to the thorax. The thorax contains the muscles that make the legs and wings move.
THE LEGS
Butterflies have six segmented legs. The two front legs of about half the butterfly species are very short. The front pair of legs are frequently used to clean the antennae. Each foot ends in a pair of grasping claws. The feet are also studded with sense organs and are used to taste food.
THE WINGS
The wings are attached to the second and third thoracic segments (the meso- and meta-thorax). During flight, the wings are held together because a lobe on the hindwing presses against the forewing.
