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Biology
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28–3 Insects
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28–3 Insects
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Insects
Class Insecta contains more species than any other group of animals.
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28–3 Insects
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What Is an Insect?
What are the distinguishing features of insects?
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28–3 Insects
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What Is an Insect?
What Is an Insect?
Insects have a body divided into three parts—head, thorax, and abdomen. Three pairs of legs are attached to the thorax.
Head Thorax Abdomen
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28–3 Insects
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What Is an Insect?
Insects have a segmented body, an exoskeleton, and jointed appendages.
A typical insect also has:
• a pair of antennae
• a pair of compound eyes
• two pairs of wings on the thorax
• tracheal tubes that are used for respiration
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28–3 Insects
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What Is an Insect?
Responses to Stimuli
Compound eyes made up of many lenses detect minute changes in color and movement.
The brain assembles information from the eye and directs the insect’s response.
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28–3 Insects
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What Is an Insect?
Insects have chemical receptors for taste and smell on their mouthparts, antennae, and legs.
Insects have sensory hairs that detect movements in the surrounding air or water.
Many insects also have well-developed ears.
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28–3 Insects
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What Is an Insect?
Adaptations for Feeding
Insects have three pairs of appendages that are used as mouthparts, including a pair of mandibles.
Insect mouthparts are specialized for feeding.
Many insects produce saliva containing digestive enzymes that help break down food.
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28–3 Insects
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What Is an Insect?
Specialized Mouthparts
Mandibles used to
saw and grind food Ant
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28–3 Insects
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What Is an Insect?
Specialized Mouthparts
Tubelike mouthpart used to suck nectar
Moth
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28–3 Insects
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What Is an Insect?
Specialized Mouthparts
Spongelike mouthpart used to lap up food
Fly
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28–3 Insects
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What Is an Insect?
Movement and Flight
Insects have three pairs of legs, which are used for walking, jumping, or capturing and holding prey.
The legs of many insects have spines and hooks that are used for grasping and defense.
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28–3 Insects
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What Is an Insect?
Flying insects typically have two pairs of wings made of chitin.
Flight has allowed insects to disperse long distances and to colonize a wide variety of habitats.
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28–3 Insects
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What Is an Insect?
What two types of development can insects undergo?
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28–3 Insects
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What Is an Insect?
Metamorphosis
The growth and development of insects usually involve metamorphosis, which is a process of changing shape and form.
Insects undergo either incomplete metamorphosis or complete metamorphosis.
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28–3 Insects
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What Is an Insect?
Immature insects that undergo incomplete metamorphosis look very much like the adults.
These immature forms are called nymphs.
Nymphs lack functional sexual organs and other adult structures, such as wings.
Nymphs gradually acquire adult structures as they molt and grow.
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28–3 Insects
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What Is an Insect?
Adult
Nymph
Nymph
Nymph
Eggs
Adult
Incomplete Metamorphosis
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28–3 Insects
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What Is an Insect?
In complete metamorphosis, animals hatch into larvae that look and act nothing like their parents.
They feed and grow rapidly and molt a few times.
They undergo a final molt and change into a pupa—the stage in which an insect changes from larva to adult.
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28–3 Insects
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What Is an Insect?
pupa
Adult Larva
Larva
Pupa
Complete metamorphosis
Adult
Eggs
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28–3 Insects
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Insects and Humans
Insects and Humans
Many insects are known for their negative effects.
Termites destroy wood structures.
Desert locusts cause billions of dollars in damage to livestock and crops.
Mosquitoes can infect humans with microorganisms that cause disease.
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28–3 Insects
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Insects and Humans
Insects also contribute to the richness of human life.
One third of the food you eat depends on plants pollinated by animals and insects.
Insects produce silk, wax, and honey.
They are considered a food delicacy in certain countries of Africa and Asia.
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28–3 Insects
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Insect Communication
Insect Communication
Insects communicate using sound, visual, chemical, and other types of signals.
Much of their communication involves finding a mate.
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28–3 Insects
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Insect Communication
Visual Cues
Male fireflies use visual cues to communicate with potential mates.
A light-producing organ in the abdomen is used to produce a distinct series of flashes.
When female fireflies see the signal, they flash back a signal of their own, inducing the males to fly to them.
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28–3 Insects
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Insect Communication
Chemical Signals
Many insects communicate using chemical signals.
The chemicals are called pheromones.
Pheromones are specific chemical messengers that affect the behavior or development of other individuals of the same species.
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28–3 Insects
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Insect Communication
Some pheromones function to signal alarm or alert other insects to the death of a member of the colony.
Other pheromones enable males and females to communicate during courtship and mating.
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28–3 Insects
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Insect Societies
What types of insects form societies?
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28–3 Insects
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Insect Societies
Insect Societies
Ants, bees, termites, and some of their relatives form complex associations called societies.
A society is a group of closely related animals of the same species that work together for the benefit of the whole group.
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28–3 Insects
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Insect Societies
Castes
Within an insect society, individuals may be specialized to perform particular tasks, or roles.
These are performed by groups of individuals called castes.
Each caste has a body form specialized for its role.
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28–3 Insects
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Insect Societies
The basic castes are:
• reproductive females (queens)
• reproductive males
• workers
Most insect societies have only one queen.
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28–3 Insects
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Insect Societies
A tropical leaf-cutter ant colony is one example of an insect society.
Individuals in the colony have specific tasks or roles.
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28–3 Insects
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Insect Societies
Major workers gather leaf tissue to use as a food source for fungus. The fungus provides food for the colony.
Smaller worker ants ride atop the leaf, keeping alert for potential threats.
Major Workers
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28–3 Insects
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Insect Societies
The queen’s sole purpose is to lay eggs.
Most of the eggs become worker ants.
Females that will become queens leave the nest to start a new colony.
Queen
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28–3 Insects
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Insect Societies
Minor worker ants chop the leaves into a fine paste, tend to the gardens, and harvest fungus for other members of the colony.
Minor Workers
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28–3 Insects
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Insect Societies
Soldier ants guard the nest from potential attackers.
Soldiers
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28–3 Insects
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Insect Societies
Communication in Societies
Each species of social insect use visual, touch, sound, and chemical signals to communicate information among members of the colony.
Honeybees communicate information about food through a series of complex movements.
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28–3 Insects
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Insect Societies
The round dance indicates that food is fairly close to the hive.
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28–3 Insects
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Insect Societies
The waggle dance indicates that food is farther away from the hive. It also indicates the direction of the food.
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28–3
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28–3
How many body parts do insects have?
a. two
b. three
c. four
d. five
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28–3
Which group contains the most species?
a. vertebrates
b. nonvertebrate invertebrates
c. noninsect arthropods
d. insects
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28–3
Characteristics shared by typical insects include
a. six walking legs and one pair of wings.
b. six walking legs and two pairs of wings.
c. eight walking legs and one pair of wings.
d. eight walking legs and two pairs of wings.
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28–3
The immature form of an insect that undergoes incomplete metamorphosis is called a(n)
a. larva.
b. nymph.
c. pupa.
d. embryo.
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28–3
Which of the following species form complex societies?
a. butterflies
b. ants
c. locusts
d. flies
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