Insects, the biological class Insecta, are part of the phylum Arthropoda. They are small terrestrial invertebrates which have a hard exoskeleton.
Insects are the largest group of animals on earth by far: there are more than 800,000 different kinds (or species) which have been described. New species of insects are continually being found: entomologists think there are millions of species still not yet discovered. There are more insects than all other kinds of animals.[1]
Insects have six legs; and most have wings. Insects were the first animals capable of flight. As they develop from eggs, insects undergo metamorphosis. Insects live all over the planet: almost all are terrestrial (live on land). Few insects live in the oceans or in very cold places, such as Antarctica. The most species live in tropical areas.
Some people call all insects "bugs", but this is not correct. Only some insects are true bugs, which is a special group of insects. People who study insects are called entomologists.
Insect bodies
File:Insect anatomy Insect anatomy A- Head
B- Thorax
C- Abdomen
1.
antenna 2. ocelli (lower)
3. ocelli (upper)
4.
compound eye 5. brain (cerebral
ganglia)
6. prothorax
7. dorsal blood vessel
8. tracheal tubes (trunk with
spiracle)
9. mesothorax
10. metathorax
11. forewing
12. hindwing
13. mid-gut (stomach)
14. dorsal tube (Heart)
15. ovary
16. hind-gut (intestine, rectum & anus)
17. anus
18. oviduct
19. nerve chord (abdominal ganglia)
20. Malpighian tubes
21. tarsal pads
22. claws
23. tarsus
24. tibia
25. femur
26. trochanter
27. fore-gut (crop, gizzard)
28. thoracic ganglion
29. coxa
30. salivary gland
31. subesophageal ganglion
32. mouthparts
.
Insects have exoskeletons (skeletons on the outside). Their skeletons are made out of thin, hard pieces or plates, like armour. All together, these pieces make a hard layer around the insect’s body. The exoskeleton protects the insect.
Just like our muscles connect to our bones to make us walk and stand up, the muscles of an insect connect to the exoskeleton to make it walk and move. Their muscles are on the inside of their skeleton.
Insects are cold-blooded, which means that they can not control their body temperature. This means that insects are not very good at surviving the cold. In the winter, most insects go into something called diapause, which is insect version of hibernation. Some insects, like cockroaches, can not go into diapause and they will die if it gets too cold outside. This is why cockroaches love living in people's warm houses!
The body of an insect has three main parts: a head, a thorax, and an abdomen. On the head are an insect’s eyes, its antennae (they feel and smell things), and its mouth. On the thorax, insects have wings and legs. All insects have six legs (three pairs) and usually four wings (two pairs). The abdomen is the back part of the insect. Inside the abdomen is the stomach, the heart, and the excretory system where body wastes pass out of the insect. Bees also have a stinger at the back of the abdomen.
How insects grow
[[File:|thumb|A mantis nymph looks just like a mantis adult but much smaller.]]
Most insects start as an egg that a female (mother) insect lays. These eggs are small; but they can usually be seen with the naked eye. Although the adults are larger, they do need a magnifying glass or a binocular microscope to see the complex details. A professional entomologist uses a binocular microscope to identify insects, plus a printed reference work.[2] There are far too many insects for anyone to remember them all, and most entomologists specialise in just one or two orders.
After the eggs hatch, two kinds of development may occur. Some insects have what is called incomplete metamorphosis. This means that a small insect, called a nymph comes out of the egg, and the nymph looks almost the same as the adult insect. As the nymph grows, it does not change the way it looks, but only how big it is. It goes through a number of stages, called 'instars'. Grasshoppers grow in this way.
Other insects have complete metamorphosis, which means that the small larva which comes out of the egg looks very different from the adult insect. Insects that have complete metamorphosis usually come out of the egg as a larva, which usually looks like a worm. The larva eats food and gets bigger until it turns into a pupa. Butterfly pupae (plural for pupa) are often inside cocoons. Inside the cocoon the insect changes the way it looks and often grows wings. When the cocoon opens, the adult insect comes out. Many insects have complete metamorphosis, for example beetles, butterflies and moths, and flies.
Kinds of insects
[[File:|thumb|A beetle (ladybird or ladybug). The red part is the hard front pair of wings.]]
Different kinds of insects can be divided into groups called orders. There are many insect orders. The biggest insect orders are listed below:
- Beetles (order Coleoptera) have the front pair of wings changed into a hard shell to protect the back wings.
- Butterflies and moths (order Lepidoptera) have large, often colourful wings.
- Flies (order Diptera) have only two wings.
- Ants, bees, and wasps (order Hymenoptera) sometimes have stingers and sometimes live in large colonies (like ant hills).
- True bugs (order Hemiptera) have a mouth that is long and narrow, like a drinking straw. This kind of mouth is called a beak.
- Grasshoppers (order Orthoptera) can usually jump with their legs. Eat grass and grain plants.
- Odonata, dragonflies and damselflies are top predators of other insects. Both aquatic nymphs and flying adults are carnivorous.
Contrary to what some people believe, spiders, scorpions, and similar animals are not insects; they are arachnids. Arachnids are arthropods that have 4 pairs of legs. Centipedes are arthropods with many legs and are also not insects.
Insects and people
People often think of insects as being either good or bad. “Good” insects are beneficial to people, meaning they do things that help people. “Bad” insects are called pests.
Pests can be harmful to people in different ways. Some are parasites, such as lice and bed bugs. Some of these parasite insects can spread diseases, such as mosquitoes spreading malaria. Other pest insects do not directly hurt people. Termites and some beetles eat wood and sometimes eat buildings, such as houses. However, termites also help break down the trees and branches that fall on the forest floor. Many insects eat agricultural products (plants meant for people to eat). Grasshoppers are one example of pest insects that eat plants in agriculture.
Many insects help people. Some kinds of insects, such as bees, make food (honey) that people can eat. The larvae of some moths make silk, which people use to make clothing. In some parts of the world, people actually eat insects. Eating insects for food is called entomophagy.
Insects help people in other ways. Many bees and flies pollinate plants. This means the insects help the plants make seeds by moving pollen from one flower to another. Some good insects eat pest insects, such as lady beetles (or ladybirds or ladybugs) eating aphids. Many insects eat dead plants and animals. This is good because, if they did not eat all the dead things, there would be dead plants and animals everywhere.
People often use poisons called insecticides to kill pest insects. Insecticides do not always work. Sometimes the pest insects become resistant to the insecticides, which means the insecticides can not hurt them anymore. Both the Colorado potato beetle and the diamondback moth are insects that are resistant to many insecticides. Insecticides do not only kill pest insects; sometimes many helpful insects are killed too. When helpful insects are killed, such as those that eat pest insects, the pest insects may come back in larger numbers than before because they are not being eaten by helpful insects anymore.
(Simplified) Taxonomy
This taxonomy lists some of the better known groups of insects.
- Archaeognatha (Jumping bristletails)
- Thysanura (Silverfish or Bristletails)
- Palaeoptera (insects that cannot flex their wings over their abdomen)
- Neoptera (Insects that can flex their wings over their abdomen)
- Plecoptera (Stone flies, about 1700 species)
- Embioptera (Webspinners, about 300 species)
- Phasmatodea (Stick insects, about 2500 species)
- Orthoptera (Grasshoppers, crickets and locusts)
- Mantophasmatidae (discovered in 2001, gladiators)
- Zoraptera (one genus, about 30 species, resemble termites)
- Dictyoptera
- Dermaptera (Earwigs)
- Grylloblattidae (ice crawlers)
- Thysanoptera (thunderflies)
- Hemiptera (true bugs, 80.000 species)
- Endopterygota (at least 680,000 species, in 11 orders)
References
- ↑ Hall, Derek 2005. Encyclopedia of insects & spiders. Grange Books. ISBN 1-84013-793-2 / 1-84013-793-2
- ↑ Either a key (a special book to helps identify insects) such as Richards O.W. 1977. Hymenoptera: Introduction and key to families (Handbooks for the identification of British insects). Royal Entomological Society, London; or a large reference work, such as Carde, Ring T. and Resh, Vincent H. (eds) 2003. Encyclopedia of Insects. Academic Press N.Y. ISBN 0-12-586990-8 / 0-12-586990-8
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