Entomology is the study of insects. Insects have three body segments - head, thorax, and abdomen. They belong to the phylum Arthropoda, whose members have jointed appendages, an exoskeleton, and segmented bodies. The major classes of arthropods are crustaceans, myriapoda, arachnids, and insects. Insects are divided into two subclasses - Apterygota, which lack wings, and Pterygota, which are winged or secondarily wingless. Important orders of insects discussed include Hemiptera, Odonata, Orthoptera, Isoptera, Coleoptera, Diptera, Lepidoptera, and

1. ENTOMOLOGY
 Entomology is defined as the study of insect
 Insect are those creatures which have three
pair of legs and the body of which is divided
into three segments i.e head, thorax and
abdomen

2. CHARACTERISTICS OF ARTHROPODA
 They have chitinous exoskeleton that shed
during growth
 Paired appendages i.e legs and antenae are
jointed
 Segmented body
 Bilateral symmetry
 Open circulatory system

3. MAJOR CLASSES OF ARTHROPODA
 Crustacean: Five or more legs, two antenae
Wings absent i.e crabs
Myriapoda: Many legs, one or two per
segment
Wings absent i.e milipede and centipede
Arachidae: Four pair of legs, No antenae,
Wings absent i.e ticks, mites and scorpion
Insecta: Have head, thorax and abdomen,
three pair of legs, paired antennae, wings

4. APTERYGOTA
 The name Apterygota is sometimes applied to a subclass of small,
agile insects, distinguished from other insects by their lack of wings in
the present and in their evolutionary history. Their first known occurrence
in the fossil record is during theDevonian period, 417–354 million years
ago.
 The nymphs (younger stages) go through little or even
no metamorphosis, hence they resemble the adult specimens. Their skin
is thin, making them appear translucent.
 Currently, no species are listed as being at conservation risk.
 Characteristics of Insect Class Apterygota
 1. Wings are primarily absent.
2. Metamorphosis is absent / slight.
3. Adults possess one or more pairs of pregenital appendages.
4. Mandibles are articulated at single point. E.g. Bristle tail, Silverfish,
Proturans, Diplurans, Japyx, and Spring tails.

5. PTERYGOTA
 The Pterygota are a subclass of insects that includes the winged
insects. It also includes insect orders that are secondarily
wingless (that is, insect groups whose ancestors once had wings
but that have lost them as a result of subsequent evolution).[1]
 The pterygotan group comprises almost all insects.
The insect orders not included are the Archaeognatha (jumping
bristletails) and the Thysanura (silverfishes and firebrats), two
primitively wingless insect orders. Also not included are the three
orders no longer considered to be insects: Protura, Collembola,
and Diplura.
 Characteristics of Insect Class Pterygota
 1. Adults are winged or secondarily wingless.
2. Metamorphosis is always present.
3. Adults do not moult and do not have pregenital appendages.
4. Mandibles are articulated with head capsule at two points.

6. ORDER HEMIPTERA
 Characteristics
The insects in this order are extremely diverse in their size, shape and colour.
The name Hemiptera means 'half wing' and all hemipterans share the following
features:

2 pairs of wings, although some species may be wingless and others have only
forewings. Wings are generally membranous but in some species the forewings
may be hardened at the base
 Piercing or sucking mouthparts appearing as a sharply pointed tube known as
a proboscis or rostrum, which extends from the underside of the head
 Compound eyes of various forms
 Antennae vary and may be either short, or long and conspicuous
 The young of hemipterans look like small adults. Some bugs may be mistaken
for beetles but can be distinguished by their mouthparts as beetles
have mandibulate mouthparts while bugs have sucking/piercing mouthparts.
 Hemiptera: bugs, aphids and cicadas

8. IMPORTANT ORDERS OF INSECTS
 Order Thysanura
 The silverfish and firebrats are found in the
order Thysanura. They are wingless insects
often found in people's attics, and have a
lifespan of several years. There are about
600 species worldwide.

9.  . Order Odonata
 Two physical features identify most members of the
order Odonata - extremely large eyes (in proportion
to its head) and a long, slender abdomen.
 Odonates are predacious as naiads and adults.
Dragonflies and damselflies have tiny antennae, so
vision is their primary means of navigating and
capturing prey. Odonates can rotate their heads
nearly 360 degrees, giving them an almost limitless
field of view.
 Several differences in wing structure separate the
Odonates from other insect groups.

10. CONT..
 Odonate eggs are laid in water, where they
hatch into wingless naiads. The naiads have
gills, and will molt up to 15 times, depending
on the species. Some naiads remain in their
aquatic environment for as long as two years
before reaching adulthood. The final molt
produces functioning wings, and the adult
dragonfly or damselfly can hunt over water or
land.

11.  Order Orthoptera
 These are familiar insects - grasshoppers,
locusts, and crickets - and one of the largest
orders of herbivorous insects.
Incomplet metamorphosis. Nymphs look
similar to mature adults, but lack fully-
developed wings.

12. CONT..
 Powerful hind legs built for jumping characterize
the Orthopteran insects. The muscular legs
propel grasshoppers and other members of the
order for distances up to 20 times their body
lengths.
 Insects in the order Orthoptera are known for
more than their jumping skills, however. Many
are accomplished singers as well. Males of
some species attract mates by producing
sounds with their legs or wings. This form of
sound production is called stridulation, and
involves rubbing the upper and lower wings or
the hind leg and wing together to create a
vibration.

13. ISOPTERA
 These social insects feed on the cellulose in
wood and wood by-products, including the
structural lumber of buildings. Termites of the
order Isoptera first appeared over 250
millions years ago. The name Isoptera
means equal wing; primary reproductive
adults have two pairs of wings, equal in
length.

14. CONT…
 Isopterans play a major role in decomposition on the
planet.
 They have pale, elongate bodies, and are sometimes
called “white ants.” Reproductive individuals have two
pairs of membranous wings, all of equal length. Termites
shed their wings after mating. To consume fibrous plant
matter, termites have chewing mouthparts.
 Their antennae are roughly the length of their heads.
 As with honeybees, the termite queen controls
reproduction. However, in the termite world, the male
reproductive or king, stays with the queen and continues
to fertilize her eggs for life.
 Termites undergo simple metamorphosis.

15. COLLEOPTRA
 Beetles have hardened forewings, called elytra,
which protect the delicate hind wings folded
beneath them.
 Beetles feeding habits are widely varied, but all
have mouthparts adapted for chewing. Many
beetles are herbivores, feeding on plants.
 Predatory beetles attack other invertebrates in
the soil or vegetation. Parasitic beetles may live
on other insects, or even mammals. A few
beetles scavenge decaying organic matter or
carrion.

16. Diptera
 Diptera is one of the largest orders, with
nearly 100,000 insects named to the order.
These are the true flies, mosquitoes, and
gnats. Insects in this group have modified
hindwings which are used for balance during
flight. The forewings function as the
propellers for flying

17.  Order Lepidoptera
 The butterflies and moths of the order
Lepidoptera comprise the second largest
group in the class Insecta. These well-known
insects have scaly wings with interesting
colors and patterns. You can often identify an
insect in this order just by the wing shape
and colo

18.  order Hymenoptera
 The order Hymenoptera includes many of the
most common insects - ants, bees, and
wasps. The larvae of some wasps cause
trees to form galls, which then provides food
for the immature wasps. Other wasps are
parasitic, living in caterpillars, beetles, or
even aphids. This is the third largest insect
order with just over 100,000 species.

19. INSECT LEGS

20. INSECT LEG CONT..
 Three pairs of jointed legs are virtually
always present in adult insects and each leg
is normally comprised of five major
segments: coxa, trochanter, femur, tibia and
tarsus. The tarsus may be further divided into
2-5 smaller segments called tarsomeres, the
last of which may bear a pair of claws.

21. INSECT LEG CONT..
 In some insects, pads (pulvilli) located beneath
the claws enable them to have greater purchase
on smooth surfaces. This may be enhanced by
densely packed small hairs on the pulvilli and in
some species, like the house fly, these hairs
exude a sticky secretion that permits them to
walk vertically up a smooth surface such as a
window pane and upside down on a ceiling.
 The coxa is attached to the thorax and the leg
segments are attached to each other by
intersegmental membranes at the joints.

22. TYPES OF INSECT LEG
 1. Cursorial legs. These are the types of legs
most people likely think of if they’ve ever
pondered insect legs before. Cursorial is a
fancy word for running, so these are the kinds of
legs you see on swiftly moving insects such as
roaches and tiger beetles. Cursorial legs tend
to be long and narrow and are designed so that
the insect can move very quickly. Things with
this type of leg are often hard to catch – or hard
to step on if you’re dealing with roaches.

23. CURSORIAL

24.  Saltatorial legs. Saltatorial legs are jumping
legs. You’ve all seen these kinds of legs
before! Grasshoppers are the poster insects for
saltatorial legs, but other jumping insects like
fleas have them as well. Saltatorial legs work
well for jumping because they are enlarged legs
filled with bulky, strong muscles. All those
muscles allow insects with this type of leg to
jump, propelling themselves forward very long
distances very quickly. Saltatorial legs are
usually hind legs.

25. SALTATORIAL

26. RAPTORIAL
 Raptorial legs. You are likely familiar with this
sort of leg too. Raptorial legs are hunting legs,
the kinds of legs you see on predatory insects
such as mantids and giant water bugs. Like the
saltatorial legs, these are enlarged legs full of
strong, powerful muscles. However, these legs
are usually at the front of the insect and are
used to grab and hold prey while they
eat. Many insects with raptorial legs hold them
out in front of their bodies, positioned so that
they can strike at prey at any time.

27. RAPTORIAL

28. NATATORIAL
 Natatorial legs. Natatorial is another word for
swimming, so insects with natatorial legs are aquatic
insects that require modified legs to move easily
through water. Natatorial legs are often flattened,
broad, and fringed with dense hairs, as in the image
of the predaceous diving beetle hind leg pictured at
right. These adaptations have the same sort of effect
as a human wearing flippers as they swim – they
increase the surface area of the legs as they kick,
allowing the insect to move more easily through
water. Many aquatic insects exhibit natatorial legs,
especially in the hind and middle pairs of legs, but not
all of them do. They are especially common in
aquatic beetles and bugs.

29. NATATORIAL

30. FOSSORIAL
 Fossorial legs. Insects with fossorial legs live
underground and use their highly modified legs,
usually the forelegs, to dig burrows. The mole
cricket, the forlegs of which are pictured at left,
are a prime example. Fossorial legs tend to be
very broad, very flat, and very dense. They
often have big, strong claws. Fossorial legs
work somewhat like shovels to rip soils apart
quickly and easily and allow the insect to bury
itself in the ground surprisingly quickly. This type
of leg is much less common than the others, but
it’s a thrill to find an insect that has them

31. FOSSORIAL

32. METAMORPHOSIS
 Metamorphosis is a biological process by
which an animal
physically develops after birth or hatching,
involving a conspicuous and relatively abrupt
change in the animal's body structure
through cell growth and differentiation
 Insect can be divided into species that
undergo complete metamorphosis
("holometaboly"), incomplete metamorphosis
("hemimetaboly"), or no metamorphosis
("ametaboly")