Insects are small animals with 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.
Studies estimate the total number of species on Earth is between six and ten million and potentially represent over 90% of the differing animal life forms on Earth.
Insects are divided into two main groups: the wingless insects like bristletails and silverfish; and the winged insects like dragonflies, cockroaches, grasshoppers, stick insects, beetles, flies, butterflies, and bees.
All insects are cold-blooded.
The lifespans of most insects are shorter than a year. With an average life of one to 24 hours, mayflies are the insect with the shortest life span. Termite queens have the longest lifespan of any insect in the world, with some queens living up to 50 years.
Adult insects can range in size from only 0.139 milometers (0.0055 inches) in wairyflies to 60 centimeters (2 feet) in stick insects [photo below]. The largest insects can weigh up to 70 grams (2.5 ounces).
All insects have sense organs that allow them to see, smell, taste, hear, and touch their environment.
The main sense organs of most insects are the antennae (feelers) on their heads. These often long and slender projections are covered with tiny sensitive hairs. Functions may variously include sensing touch, air motion, heat, vibration (sound), and especially smell or taste.
Instead of lungs, insects breathe with a network of tiny tubes called tracheae. Air enters the tubes through a row of holes along an insect’s abdomen. The air then diffuses down the blind-ended tracheae.
Adult insects typically move about by walking, flying or sometimes swimming.
Many insects are camouflaged, so that predators do not see them. Some species are armed with stingers or foul-tasting poison. Many of these have bright colors, such as black-and-yellow stripes, to warn enemies away.
Insects are mostly solitary, but some, such as certain bees, ants and termites, are social and live in large, well-organized colonies.
Insects have many different ways of communicating. They communicate through touch with their antennae and mouths; visually through combinations of flashes of light and combinations of colour; they make sounds to attract others of their own species or to send out signals to other species; and by smell: they produce chemicals called pheromones to send signals to within a species and chemicals called allomones for the warning signals that insects send out to other species.
Many adult insects die off in winter. Their eggs or young survive in sheltered places and emerge in spring. Some insects survive the cold by hibernating. Others, such as monarch butterflies [photo below], migrate long distances to avoid the winter chill.
Insects eat a huge range of foods. Around half are plant-eaters, feeding on leaves, roots, seeds, nectar, or wood. There are insects that eat other insects, and some even drink blood. And some insects will eat whatever scraps of food you leave lying around.
Some insects get enough water from their food, be it moist plants or goo-filled prey, but others do need to drink water! They don’t need much, however: a simple raindrop will do.
Depending on the species, insects may reproduce either sexually or asexually.
All insects go through the same life cycle. Life begins as an egg. The egg hatches and larva emerge. Larvae usually look nothing like the adult insect. The larvae enter a pupa, chrysalis or cocoon. An adult insect emerges from the pupa.
Most insects take little or no care of their young, but social insects are an exception.
Insects evolved from a group of crustaceans. They were the first animals to develop flight, about 400 million years ago in the Devonian period. The oldest definitive insect fossil, Rhyniognatha hirsti, is estimated to be 407 to 396 million years old.
Beetles, of the insect order Coleoptera, are the most biodiverse group of creatures known, with more than 380,000 species described to date, making up 40 percent of all insect species on the books.
All bugs are insects, but not all insects are bugs. Not every insect is a bug. Strictly speaking, “bugs” are an order of insects called Hemiptera.
Spiders are not insects.
There are about 1.4 billion insects for every person on Earth. The total weight of all the insects is about 70 times as much as all the people.
Silkworms and bees have been used extensively by humans for the production of silk and honey, respectively.
An Australian tiger beetle is probably the world’s fastest running insect. A fierce hunter, it can reach speeds of 9 kilometers (5.6 miles) per hour when chasing prey.
The fastest flying insect is Horse fly. It’s fastest recorded speed has been up to 145 kilometers (90 miles) per hour. Not only is this insect very fast, but it also has great control and maneuvers in the air.
Hercules beetles can lift 850 times their own weight. That’s equivalent to a human lifting 10 elephants.
Locusts can eat their own weight in food in a day.
The praying mantis is the only known insect that can turn its head and look over its shoulder.
The only insect indigenous to Antarctica is the wingless midge Belgica antarctica.
Scarab beetles held religious and cultural symbolism in Old Egypt, Greece and some shamanistic Old World cultures.
In some cultures, insects, especially deep-fried cicadas, are considered to be delicacies, whereas in other places they form part of the normal diet.