28–3 Insects
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28–3 Insects
What Is an Insect?
What Is an Insect?
Class Insecta contains more species than any other
group of animals.
The number of living orders varies from 26 to more
than 30 because biologists cannot agree on how to
classify them.
Insects have a body divided into three parts—head,
thorax, and abdomen. Three pairs of legs are attached
to the thorax.
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28–3 Insects
What Is an Insect?
Insects have a segmented body, an exoskeleton, and
jointed appendages.
A typical insect also has:
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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
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.
Compound eyes produce an image less detailed
than what we can see, however they are far better
at detecting movement.
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28–3 Insects
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 that
hear sounds far above the human range, located in
odd places (behind the legs in grasshoppers).
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28–3 Insects
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
What Is an Insect?
Specialized Mouthparts
Mandibles used to
saw and grind food
Ant
Tubelike mouthpart
used to suck nectar
Moth
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Spongelike mouthpart
used to lap up food
Fly
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28–3 Insects
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.
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
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
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
What Is an Insect?
In complete metamorphosis,
animals hatch into larvae that
look and act nothing like their
parents.
They feed voraciously, 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
Insects and Humans
Insects and Humans
Many insects are known for their negative effects.
Termites destroy wood structures, bees and wasps
give painful stings, moths eat through clothing, etc.
Mosquitoes can infect humans with microorganisms
that cause disease such as malaria.
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
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
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
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.
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
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
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
Insect Societies
The basic castes are:
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reproductive females (queens) – lay eggs
reproductive males – fertilize eggs
workers – feeding, building, protection
Most insect societies have only one queen, which is
typically the largest individual of the colony.
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28–3 Insects
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
Insect Societies
The round dance
indicates that food
is fairly close to
the hive.
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28–3 Insects
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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