This document discusses insects and their characteristics. It begins by defining insects as arthropods in the class Insecta, having a three-part body, six legs, two antennae, and sometimes undergoing complete metamorphosis. It notes that insects are among the most diverse and numerous animal groups, living in most habitats except the ocean. The life cycles of insects typically involve hatching from eggs and developing through molting or metamorphosis until reaching the adult stage.

3. The study of these traditional
reptile groups, historically
combined with that of modern
amphibians, is called
herpetology. Birds are also often
included as a sub-group of
reptiles by modern scientists.[1]
Some early examples include the lizard-like Hylonomus and
Casineria. In addition to the living reptiles, there are many
diverse groups that are now extinct, in some cases due to
mass extinction events.
are a group (Reptilia) of tetrapod animals
comprising today's turtles, crocodilians,
snakes, lizards, tuatara, and their extinct
relatives.

4. Some birds, especially corvids and parrots, are among
the most intelligent animals; several bird species make
and use tools, and many social species pass on
knowledge across generations, which is considered a
form of culture.
Birds have wings which are more or less
developed depending on the species; the
only known groups without wings are the
extinct moas and elephant birds.
Wings, which evolved from forelimbs, give most birds the ability to fly,
although further speciation has led to some flightless birds, including
ratites, penguins, and diverse endemic island species of birds.

5. The digestive and the aforementioned flightless
penguins, and also members of the duck family, have
also evolved for swimming. Birds,
specificallrespiratory systems of birds are also
uniquely adapted for flight. Some bird species of
aquatic environments, particularly y Darwin's finches,
played an important part in the inception of Darwin's
theory of evolution by natural selection.

6. Animals are divided into various sub-groups, some of which are:
vertebrates (birds, mammals, amphibians, reptiles, fish); molluscs
(clams, oysters, octopuses, squid, snails); arthropods (millipedes,
centipedes, insects, spiders, scorpions, crabs, lobsters, shrimp); annelids
(earthworms, leeches); sponges; jellyfish. and Animals
Animals are multicellular, eukaryotic organisms
of the kingdom Animalia (also called Metazoa).
All animals are motile, meaning they can move
spontaneously and independently, at some point
in their lives.
Most known animal phyla appeared in
the fossil record as marine species
during the Cambrian explosion, about
542 million years ago

7. The word "animal" comes from the Latin word animalis, meaning
"having breath", "having soul, and, "living beings".[1] In everyday non-
scientific usage the word excludes humans – that is, "animal" is often
used to refer only to non-human members of the kingdom Animalia;
often, only closer relatives of humans such as mammals, or mammals
and other vertebrates, are meant.[2] The biological definition of the
word refers to all members of the kingdom Animalia, encompassing
creatures as diverse as sponges, jellyfish, insects, and humans.[3

8. They are among the most diverse groups of animals on the planet,
including more than a million described species and representing more
than half of all known living organisms.[2][3] The number of extant species
is estimated at between six and ten million,[2][4][5] and potentially
represent over 90% of the differing animal life forms on Earth.[6] Insects
may be found in nearly all environments, although only a small number of
species reside in the oceans, a habitat dominated by another arthropod
group, crustaceans.
Insects (from Latin insectum, a calque of Greek
ἔντομον [éntomon], "cut into sections") are a class
of invertebrates within the arthropod phylum that
have a chitinous exoskeleton, a three-part body
(head, thorax and abdomen), three pairs of jointed
legs, compound eyes and one pair of antennae.

9. The life cycles of insects vary but most
insects hatch from eggs. Insect growth
is constrained by the inelastic
exoskeleton and development involves
a series of molts. The immature stages
can differ from the adults in structure,
habit and habitat, and can include a
passive pupal stage in those groups
that undergo 4-stage metamorphosis
(see holometabolism).
Insects that undergo 3-stage metamorphosis lack a pupal stage and
adults develop through a series of nymphal stages.[7] The higher level
relationship of the hexapoda is unclear. Fossilized insects of enormous
size have been found from the Paleozoic Era, including giant dragonflies
with wingspans of 55 to 70 cm (22–28 in). The most diverse insect
groups appear to have coevolved with flowering plants.