Metamorphosis

Metamorphosis is the change in shape that insects undergo as they grow. There are two types of transformations: complete, like that of monarch butterflies, and incomplete, like that of dragonflies or grasshoppers. Insects with complete metamorphosis pass through an immobile state (called the pupal, or chrysalid, phase) in which their body is transformed by hormones within a cocoon. •

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j Larva or caterpillar I^H

makes its entry into the world by eating its shell. From then on, eating and growing will be its main activities. Every time it sheds its skin, the old exoskeleton is broken. The insect forms a new, soft exoskeleton, which is gradually expanded by blood pressure. The exoskeleton then undergoes a chemical reaction that hardens it.

3 weeks

IS THE AMOUNT OF TIME THE INSECT LIVES IN THE LARVAL STAGE.

In the Beginning, the Egg

The adult female lays eggs among the leaves, where they will be protected. Monarch butterfly eggs have colors ranging from grayish-white to cream, and they are shaped like barrels, 0.1 inch (2 mm) in diameter. The larvae grow inside the egg until they hatch; after hatching, they eat the shell.

MATING AND EGG LAYING

When monarch butterflies mate, they stay joined all afternoon and evening, until the next morning, for a total of 16 hours. After their first mating, the females lay eggs.

MATING AND EGG LAYING

When monarch butterflies mate, they stay joined all afternoon and evening, until the next morning, for a total of 16 hours. After their first mating, the females lay eggs.

7 days

AMOUNT OF TIME THE LARVA LIVES INSIDE THE EGG

FIVE CHANGES

When it hatches, the insect is shaped like a worm. This caterpillar will molt its exoskeleton five times as it grows in size. Its internal structure will not change, however. Each new exoskeleton is larger than the one before.

Hatching from the egg

The exoskeleton hardens. As the insect grows, the exoskeleton becomes too small. Eventually it splits and falls off.

>* Second shedding

Simple Metamorphosis

Also called incomplete metamorphosis, because, unlike complete metamorphosis, it does not include a pupal phase. The wings and legs develop gradually, so that the insect does not need to spend a certain amount of time immobile. Locusts, cockroaches, termites, and dragonflies have this type of metamorphosis. From an evolutionary standpoint, it corresponds to ancient or primitive insects. One of its characteristics is the nymph stage of young insects. The nymph gradually changes in shape as it grows. When it sheds its exoskeleton, the adult emerges.

Hatching from the egg

The exoskeleton hardens. As the insect grows, the exoskeleton becomes too small. Eventually it splits and falls off.

>* Second shedding

EMPEROR DRAGONFLY

Anax imperator

INSIDE THE LARVA

The insect's heart, nervous system, and breathing system are almost completely developed during the larval stage, and they change very little afterward. The reproductive system is formed later.

A SIMPLE ASSIGNMENT

In the caterpillar phase, the insect focuses solely on eating leaves. In this way it accumulates the necessary energy for the physiological processes of metamorphosis. For digesting the leaves, the caterpillar has a very simple digestive track.

CREMASTER

The caterpillar secretes a fibrous cushion that sticks to the stalk of a plant. It hangs from the cushion with hooks on the end of its abdomen.

EXOSKELETON

Crossed with yellow, black, and white stripes, it is soft after every shedding and later hardens. The insect always emerges head first.

EMPEROR DRAGONFLY

Anax imperator

INSIDE THE LARVA

The insect's heart, nervous system, and breathing system are almost completely developed during the larval stage, and they change very little afterward. The reproductive system is formed later.

INTESTINE

INTESTINE

PREPARATION FOR THE PUPAL PHASE

Before passing to the next stage, the larva stops eating and eliminates any food left in its digestive tract. The juvenile hormone, which keeps the transformation of the body in check, starts to become inhibited.

TO THE OLD BODY

The larva's last exoskeleton begins to fall off and is replaced by a greenish tissue that will form the cocoon, or chrysalis.

TO THE OLD BODY

The larva's last exoskeleton begins to fall off and is replaced by a greenish tissue that will form the cocoon, or chrysalis.

72 INSECTS

Pupa (chrysalis) IHI

After getting rid of its larval exoskeleton, the insect hangs immobile from a branch, protected by a cocoon. Inside, it will develop its distinctive butterfly form. Although it does not eat during this period, it is intensely active biologically and undergoes considerable change. Histolysis, a process in which the larva's structures are transformed into the material that the insect will use to develop adult structures, takes place at this time.

HISTOGENESIS

New tissues are generated from hemolymph (the equivalent of blood), the Malpighian tubules (the energy-producing organ in insects), and histolyzed tissue, including the larva's muscles. The monarch butterfly pupa is called a chrysalis because of the color and structure of the capsule that protects it. It is oval-shaped with gold and black spots.

LENGTH OF THE PUPA, ^^ OR CHRYSALIS, PHASE

Adult

After reaching its final shape, the butterfly will not grow any more. When the butterfly emerges from its cocoon, its wings are still wrinkled and damp. It will need to hang upside down to stretch them out to dry, so that they will be useful for flying. This will take several hours of waiting and struggling. From then on, the butterfly will feed on nectar.

BUTTERFLY SHAPE

The adult butterfly's wings and legs develop from the cuticle, or skin tissue, which is composed mostly of chitin. Other organs are preserved or rebuilt from regenerative cells.

-CAMOUFLAGE

The chrysalid capsule has shapes, textures, and colors that help keep it from being noticed, to protect it from predators. The capsules typically resemble leaves or bird droppings.

HORMONES IN FULL

SWING

Metamorphosis is governed by three hormones. One is the cerebral (brain) hormone, which stimulates the prothoracic gland. This gland produces the molting hormone ecdysone, which causes the loss of the old skin. The third hormone is the juvenile hormone, which slows down the transformation to the adult stage.

WITHIN SIGHT

As the time draws near for the adult to emerge, the chrysalis becomes thinner, changes color, and becomes transparent. The transformed insect can be seen inside.

BREAKING FREE

To permit the butterfly to emerge, the mature capsule splits along its length. The insect gradually stretches its new body and activates the circulation of the hemolymph.

FLY AWAY, BUTTERFLY

The lifespan of this insect in its adult phase will depend on its luck, its migrations, and the attacks of predators . . .

from 5 to 7 weeks

YOUNG ADULT

Once free of its covering, the adult is usually pale in color, and its wings are soft and folded. After about 40 minutes the wings expand, harden, and take on their full color.

ELIMINATING WASTES

While emerging, the butterfly secretes a fluid containing the waste produced during the chrysalis phase. This fluid, called meconium, is considered rather foul-smelling.

INTERNAL ORGANS

Inside the chrysalis, the insect's body is changing into that of an adult. The intestine rolls into a spiral shape to assimilate liquid food, and the reproductive organs are developing for the adult stage.

INTESTINE

TRANSFORMATIONS OF THE FLY

This side diagram shows the changes in the organs of a fruit fly (Drosophila sp.) from the pupa stage to the adult stage. The cuticle of the last larval stage protects the pupa. This transparent membrane allows the wings, the antennae, and the folded legs to be seen while they are forming. The pupa already has the dimensions of the adult flying insect, and it will not grow any bigger during the rest of its life.

Mouth_

. Antennae

' Wings

Vi fi1

■ Reproductive organs w

JOINED, BUT NOT FOREVER

After leaving the chrysalis, monarch butterflies from the same litter stay together for a period of three to eight days before they go their separate ways.

UPS AND DOWNS OF LIFE AS AN ADULT

Mating, reproducing, and laying tiny eggs to give rise to new generations will be the main activities of the adult insect. Each female lays an average of 100-300 eggs during her life.

Order and Progress

Ants are one of the insects with the highest social organization. In the anthill, each inhabitant has a job to do. The head of the family is the queen, the only one that reproduces. All the rest of the ants are her offspring. During mating, queens and drones (males) from various colonies mate on the wing. The queens need to mate several times, because the sperm they receive will have to last their lifetime.®

The Castes

Each ant plays a role in the nest and is assigned its role at birth. Drone, soldier, worker, and replete worker (which stores food reserves) are the castes that distinguish what chores each ant will have.

perceive odors and transmit messages.

The Castes

Each ant plays a role in the nest and is assigned its role at birth. Drone, soldier, worker, and replete worker (which stores food reserves) are the castes that distinguish what chores each ant will have.

perceive odors and transmit messages.

The most widely used defense is biting and spraying streams of formic acid. Soldier ants have the job of scaring away the enemy because they have larger heads than worker ants.

American farmer ant

Clamping jaw

EGGS LARVAE NYMPHS

may contain formic acid and can kill or paralyze the prey. It comes from special glands in the lower abdomen.

NYMPHS

COCOON

The most widely used defense is biting and spraying streams of formic acid. Soldier ants have the job of scaring away the enemy because they have larger heads than worker ants.

American farmer ant

Clamping jaw

EGGS LARVAE NYMPHS

LARVAE

are carried to another chamber to grow.

are laid by the queen in the lowest area.

are laid by the queen in the lowest area.

are fed and taken care of in another area.

INTERCHANGE OF FOOD

Having two stomachs, an ant can share food. The transfer begins when the receiving ant uses its front legs to touch the lip of the donor ant.

Stomach

Individual pouch may contain formic acid and can kill or paralyze the prey. It comes from special glands in the lower abdomen.

SOUTHERN WOOD ANT

Formica rufa

The new ants hatch ready to work.

LO sti

Poisonous stinger

Abdomen

TRAP-JAW ANT

Odontomachus bauri

NYMPHS

COCOON

COCOONS

QUEEN ANT

76 INSECTS

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