See text .
INSECTS or INSECTA (from
Latin insectum, a calque of Greek
ἔντομον , "cut into sections") are by far the largest group of
hexapod invertebrates within the arthropod phylum . Definitions and
circumscriptions vary; in one approach insects comprise a class within
Phylum Arthopoda. As the term is used here, it is synonymous with
Insects have a chitinous exoskeleton , a three-part body (head ,
thorax and abdomen ), three pairs of jointed legs , compound eyes and
one pair of antennae . They are the most diverse group of animals on
the planet, including more than a million described species and
representing more than half of all known living organisms . The
number of extant species is estimated at between six and ten million,
and potentially represent over 90% of the differing animal life
forms on Earth.
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 .
The life cycles of insects vary but most 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
Insects that undergo 3-stage metamorphosis lack a
pupal stage and adults develop through a series of nymphal stages.
The higher level relationship of the
Hexapoda is unclear. Fossilized
insects of enormous size have been found from the
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 .
Adult insects typically move about by walking, flying or sometimes
swimming (see § Locomotion below). As it allows for rapid yet stable
movement, many insects adopt a tripedal gait in which they walk with
their legs touching the ground in alternating triangles.
the only invertebrates to have evolved flight. Many insects spend at
least part of their lives under water, with larval adaptations that
include gills , and some adult insects are aquatic and have
adaptations for swimming. Some species, such as water striders , are
capable of walking on the surface of water.
Insects are mostly
solitary, but some, such as certain bees , ants and termites , are
social and live in large, well-organized colonies. Some insects, such
as earwigs , show maternal care, guarding their eggs and young.
Insects can communicate with each other in a variety of ways. Male
moths can sense the pheromones of female moths over great distances.
Other species communicate with sounds: crickets stridulate , or rub
their wings together, to attract a mate and repel other males.
Lampyridae in the beetle order communicate with light.
Humans regard certain insects as pests , and attempt to control them
using insecticides and a host of other techniques. Some insects damage
crops by feeding on sap, leaves or fruits. A few parasitic species are
pathogenic . Some insects perform complex ecological roles; blow-flies
, for example, help consume carrion but also spread diseases. Insect
pollinators are essential to the life cycle of many flowering plant
species on which most organisms, including humans, are at least partly
dependent; without them, the terrestrial portion of the biosphere
(including humans) would be devastated. Many other insects are
considered ecologically beneficial as predators and a few provide
direct economic benefit. Silkworms and bees have been used extensively
by humans for the production of silk and honey , respectively. In some
cultures, people eat the larvae or adults of certain insects.
* 1 Etymology
* 2 Definitions
Phylogeny and evolution
* 3.1 Evolutionary relationships
* 3.2 Taxonomy
* 4 Diversity
* 5 Morphology and physiology
* 5.1 External
* 5.2 Segmentation
* 5.3 Internal
* 5.3.2 Digestive system
* 126.96.36.199 Midgut
* 5.3.3 Reproductive system
* 5.3.4 Respiratory system
* 6 Reproduction and development
* 6.1.1 Incomplete metamorphosis
* 6.1.2 Complete metamorphosis
* 7 Senses and communication
* 7.1 Light production and vision
* 7.2 Sound production and hearing
* 7.3 Chemical communication
* 8 Social behavior
* 8.1 Care of young
* 9 Locomotion
* 9.1 Flight
* 9.2 Walking
* 9.2.1 Use in robotics
* 9.3 Swimming
* 10 Ecology
* 10.1 Defense and predation
* 11 Relationship to humans
* 11.1 As pests
* 11.2 In beneficial roles
* 11.3 In research
* 11.4 As food
* 11.5 In culture
* 12 See also
* 13 References
* 14 Bibliography
* 15 Further reading
* 16 External links
The word "insect" comes from the
Latin word insectum, meaning "with a
notched or divided body", or literally "cut into", from the neuter
singular perfect passive participle of insectare, "to cut into, to cut
up", from in- "into" and secare "to cut"; because insects appear "cut
into" three sections.
Pliny the Elder
Pliny the Elder introduced the
as a loan-translation of the Greek word ἔντομος (éntomos) or
"insect" (as in entomology ), which was
Aristotle 's term for this
class of life, also in reference to their "notched" bodies. "Insect"
first appears documented in English in 1601 in Holland 's translation
of Pliny. Translations of Aristotle's term also form the usual word
for "insect" in Welsh (trychfil, from trychu "to cut" and mil,
Serbo-Croatian (zareznik, from rezati, "to cut"), Russian
(насекомое nasekomoje, from seč'/-sekat', "to cut"), etc.
The precise definition of the taxon Insecta and the equivalent
English name "insect" varies; three alternative definitions are shown
in the table.
Definition of Insecta
Insecta sensu lato
Diplura (two-pronged bristletails)
Archaeognatha (jumping bristletails)
Insecta sensu stricto
Pterygota (winged insects)
Insecta sensu strictissimo
In the broadest circumscription , Insecta sensu lato consists of all
hexapods . Traditionally, insects defined in this way were divided
into "Apterygota" (the first five groups in the table) – the
wingless insects – and
Pterygota – the winged insects. However,
modern phylogenetic studies have shown that "Apterygota" is not
monophyletic, and so does not form a good taxon. A narrower
circumscription restricts insects to those hexapods with external
mouthparts, and comprises only the last three groups in the table. In
this sense, Insecta sensu stricto is equivalent to Ectognatha. In
the narrowest circumscription, insects are restricted to hexapods that
are either winged or descended from winged ancestors. Insecta sensu
strictissimo is then equivalent to Pterygota. For the purposes of
this article, the middle definition is used; insects consist of two
Archaeognatha (jumping bristletails) and Zygentoma
(silverfish), plus the winged or secondarily wingless Pterygota.
PHYLOGENY AND EVOLUTION
This section needs to be UPDATED. Please update this article to
reflect recent events or newly available information. (July 2017)
Evolution of insects
Crustacea (crabs , shrimp , isopods , etc.)
Arachnida (spiders , scorpions , mites , ticks , etc.)
Eurypterida (sea scorpions: extinct)
Xiphosura (horseshoe crabs)
Pycnogonida (sea spiders)
A phylogenetic tree of the arthropods and related groups
Evolution has produced enormous variety in insects. Pictured are
some of the possible shapes of antennae .
The evolutionary relationship of insects to other animal groups
Although traditionally grouped with millipedes and centipedes
—possibly on the basis of convergent adaptations to
terrestrialisation —evidence has emerged favoring closer
evolutionary ties with crustaceans . In the
insects, together with
Remipedia , and
make up a natural clade labeled Miracrustacea .
A report in November 2014 unambiguously places the insects in one
clade, with the crustaceans and myriapods , as the nearest sister
clades. This study resolved insect phylogeny of all extant insect
orders, and provides "a robust phylogenetic backbone tree and reliable
time estimates of insect evolution."
Other terrestrial arthropods, such as centipedes, millipedes,
scorpions , and spiders , are sometimes confused with insects since
their body plans can appear similar, sharing (as do all arthropods) a
jointed exoskeleton. However, upon closer examination, their features
differ significantly; most noticeably, they do not have the six-legged
characteristic of adult insects.
The higher-level phylogeny of the arthropods continues to be a matter
of debate and research. In 2008, researchers at Tufts University
uncovered what they believe is the world's oldest known full-body
impression of a primitive flying insect, a 300 million-year-old
specimen from the
Carboniferous period . The oldest definitive insect
fossil is the
Rhyniognatha hirsti , from the
Rhynie chert . It may have superficially
resembled a modern-day silverfish insect. This species already
possessed dicondylic mandibles (two articulations in the mandible), a
feature associated with winged insects, suggesting that wings may
already have evolved at this time. Thus, the first insects probably
appeared earlier, in the
Four super radiations of insects have occurred: beetles (evolved
about 300 million years ago), flies (evolved about 250 million years
ago), and moths and wasps (evolved about 150 million years ago).
These four groups account for the majority of described species. The
flies and moths along with the fleas evolved from the
The origins of insect flight remain obscure, since the earliest
winged insects currently known appear to have been capable fliers.
Some extinct insects had an additional pair of winglets attaching to
the first segment of the thorax, for a total of three pairs. As of
2009, no evidence suggests the insects were a particularly successful
group of animals before they evolved to have wings.
Carboniferous and Early
Permian insect orders include both
extant groups, their stem groups, and a number of
now extinct. During this era, some giant dragonfly-like forms reached
wingspans of 55 to 70 cm (22 to 28 in), making them far larger than
any living insect. This gigantism may have been due to higher
atmospheric oxygen levels that allowed increased respiratory
efficiency relative to today. The lack of flying vertebrates could
have been another factor. Most extinct orders of insects developed
Permian period that began around 270 million years ago.
Many of the early groups became extinct during the Permian-Triassic
extinction event , the largest mass extinction in the history of the
Earth, around 252 million years ago.
The remarkably successful
Hymenoptera appeared as long as 146 million
years ago in the
Cretaceous period, but achieved their wide diversity
more recently in the
Cenozoic era, which began 66 million years ago. A
number of highly successful insect groups evolved in conjunction with
flowering plants , a powerful illustration of coevolution.
Many modern insect genera developed during the Cenozoic.
this period on are often found preserved in amber , often in perfect
condition. The body plan, or morphology , of such specimens is thus
easily compared with modern species. The study of fossilized insects
is called paleoentomology .
Insects are prey for a variety of organisms, including terrestrial
vertebrates. The earliest vertebrates on land existed 400 million
years ago and were large amphibious piscivores . Through gradual
evolutionary change, insectivory was the next diet type to evolve.
Insects were among the earliest terrestrial herbivores and acted as
major selection agents on plants. Plants evolved chemical defenses
against this herbivory and the insects, in turn, evolved mechanisms to
deal with plant toxins. Many insects make use of these toxins to
protect themselves from their predators. Such insects often advertise
their toxicity using warning colors. This successful evolutionary
pattern has also been used by mimics . Over time, this has led to
complex groups of coevolved species. Conversely, some interactions
between plants and insects, like pollination , are beneficial to both
Coevolution has led to the development of very specific
mutualisms in such systems.
See also: Category:
Insect orders and Category:
Archaeognatha - 470