Mantid head

Insects have been around longer than any other forms of terrestrial life. They have existed for over 320 million years, evolving from millipedes which in turn evolved for crustaceans in the sea. Cockroaches and termites and dragonflies are the oldest insects..

Insects are the most widely dispersed and the most numerous of an animals. They can be found in the oceans, on polar ice caps and flying over the Himalayas and living in steaming hot volcanic springs. According to one calculation there are about 1,000, 000, 000,000,000,000,000 (one million trillion) insects in the earth, more than a billion for every human being.

Of the 2 million or so known species of plants and animals about 700,000 of them are insects. New insects are discovered and named at a rate of about 2,000 a year. Thousands — perhaps millions more wait to discovered. In terms of weight, insects account roughly for 85 percent of all animal life forms, All the world’s insect weigh more that 12 times all the world's people.

Insects, centipedes, millipedes, arachnids (including spiders and scorpions) and crustaceans belong to the phylum of arthropods. Arthropods account for three fourths of all known animals. All have exoskeletons made of chitin; a body divided into segments and protected by cuticle; jointed legs arranged in pairs; an open circulatory system with organs bathed in a liquid called hemolymph that is pumped around the body by the heart; and a nervous system comprised of paired nerve chords.

Insects hatch from eggs as larvae or grub that often resemble short, stubby worms. They then become pupa and finally metamorphose into a full-grown insect. As they grow the shed their old skins exoskeletons and grow new ones. Larvae and pupa spend much of their time eating. Unlike bird eggs, insects eggs contain very little yoke or food. Instead the eggs are laid on or near food sources and the young begin eating as soon as they hatch. The primarily purpose of insects is to reproduce.

Websites and Resources on Insects: ; Insect ; BBC Insects ; Insect and Arachnid ; Wikipedia article Wikipedia ; Virtual Insect ; National Geographic on Bugs National Geographic ; Smithsonian bug info ; Entomology for Beginners ; BugGuide ;

Websites and Resources on Animals: ARKive Animal Info ; Animal Picture Archives (do a Search for the Animal Species You Want) animalpicturesarchive ; BBC Animals Finder ; Animal Diversity Web ; International Field Guides ; ; Encyclopedia of Life ; World Wildlife Fund (WWF) ; National Geographic National Geographic ; Animal Planet ; Wikipedia article on Animals Wikipedia ; ; Endangered Animals ; Endangered Species Resource List ; Biodiversity Heritage Library

Insect Characteristics

All insects have six legs (three pairs of legs) and a body divided into three distinct parts: 1) a head with a mouth and most of the sensory organs; 2) a muscle-filled thorax that provides platform for the legs; and 3) an abdomen housing the organs used in digestion and reproduction.

All three body are housed on an external skeleton comprised of chiltin and coated with a protein call sclerotin that makes it hard. Chilton is tough, flexible and permeable. It is the same material in crab and lobster shells. It was developed 530 million years ago by crustaceans and has a chemical composition to similar to that of cellulose. The one drawback with an external skeleton is that it has to be shed when the insects grows. Molting refers to process of shedding one exoskeleton and growing another. The energy and time expended in molting is one thing that limits insect size.

Most insects have antennae that can detect molecules or scents. Most are deaf. Those that can hear are generally noisemaking insects such as cicadas and crickets. Many also have a long thing mouth part, pointed at the tip and capable if being thrust like a miniature drill deep into a plant or animal and used like a straw to suck juices. Inside the tube are two hollow canals, one for transporting the sucked-up juices into the mouth and the other for secreting saliva.

Insects don't have lungs. Instead they rely on their trachea and a system of tubes running to every part of the body to absorb oxygen and expel carbon dioxide. They are prevented from getting any bigger than they are by their breathing system. The tubes — which are connected to openings called spiracles — work well over short distances but lose their efficiency as they become longer. This is why you don't find crickets the size of crocodiles or ants the size of armadillos. But what about the huge dragonflies that lived before the age of the dinosaurs?

The legs are composed of segments connected by ball and socket joints. The muscles that move the legs are connected to the inner surface of the exoskeleton. This is the opposite of vertebrates in which muscles are attached to the outsides of internal bones.

Insect Colors and Deception

Some beetles get a metallic sheen and dazzling colors not from pigments but from optical features that reflect specific wavelengths of color. These structural colors, which don’t fade and are more brilliant than those produced by pigments, are of great interest to companies that make paint, cosmetics and holograms for credit cards.

Investigations of the iridescence in butterflies and beetles and anti-reflective coatings in moth’s eyes have helped produce brighter screens for cell phones and a secret anti-counterfeiting technique.

Insect Horns

Douglas J. Emlen, a biologist at the University of Montana, has studied insects and other animals with massive horns and other strange weapon-like morphologies. He found that creatures were more likely to develop such weapons when there was some resources that could be monopolized and used to attract females, with the weapons being used to fight off males. The cost of developing and carrying the often heavy and cumbersome weapons is outweighed by the greater access to females, owing to the possession of some prized food source or a place where females could lay their eggs.

Emlen also found, interestingly, that the larger and more fearsome-looking the weapons the less violence there was. The smaller weapons were often quite destructive because the only function they served was as an instrument for fighting. Larger more menacing weapons allowed males to size each other up and determine whether it was worthwhile to engage in battle, with smaller outclassed males avoiding combat if it appeared they were likely to lose. The weapons, when studied over evolutionary time, often started out as small bumps of chiton or bone and then grew bigger.

Emlen wrote in the March 2009 edition of the Annual Review of Ecology, Evolution and Systematics, “The most elaborate weapons rarely inflict real damage to opponents but the structures are very effects at revealing even subtle differences among males in their size, status and physical condition.”

World’s Largest Insects

Among the longest, largest and fearsome-looking insects are 30-centimeter-long walking sticks, and predatory water bugs with front legs that have evolved into long, wicked, sickle-like pincers used for snaring prey. The largest of these water bugs are as big as a man’s hand and capable, according to some, of putting a hole in it.

Wetas are the world's largest insects. Found only in New Zealand, they are basically crickets without wings that have changed little in the last 200 million years. There are ten different species of weta. The largest species lives on Barrier Island off the coast of the North Island. It weighs about 2.5 ounces and is about the size of a mouse. [Source: Mark Moffet, National Geographic, November 1991]

Different species of weta inhabit different regions of the country. The most common species, the tree weta, is found mostly in lowland forests. It is large enough to fill a man's hand and when it is alarmed it kicks with its back legs.


Mantids are long predatory insects that include praying mantises. In temperate climates mantids hatch in the spring and grow and molt during the summer months. By autumn they have reached adulthood and are ready to begin mating. Mantids lay their eggs inside protective sacs called ootheca, The sac is made of foam secreted by the females along with her eggs. At first the foam is soft, but when it come in contact with air it hardens into a tough, fiber-like material that protects the eggs throughout the long winter months. The adults all die off with the onset of cold weather.

Mantids are first rate hunters. Rather than stalk prey they wait patiently, well camouflaged against their backgrounds, grabbing unsuspecting prey as they pass by with a quick lung. Sharp jaws are used to cut the prey into bit-size pieces. One of their favorite places to catch prey is just below blooming flowers where they wait to pounce on insects coming to the flower to sip nectar or collect pollen.

A mantid’s front pair of legs are lined with barbs that are designed to seize and hold prey. At the tips of each of these legs is a large, curved spike, which is often used to like a grappling hook to make the initial grab. Once the prey is secured in between the legs the mantis methodically tears the prey to pieces and eats it.

Water Insects

Water striders have three pairs of legs like all insects. The long middle and rear legs are used to scull the insect over the water surface with surprising busts of speed. The front legs are shorter and used for holding prey. All water striders legs’s are covered with millions of tiny hairs that trap air bubbles and keep the insect on the surface of the water. In addition, water repelling oils are secreted from glands at the tip of the legs and the insects light weight (it weigh less than 1.10th of a gram) also help to keep them aloft.

When an insects falls into the water and starts struggling to get out it sets off a series of ripples that spread across the water and the sensitive antennae of water striders can pick up. When the water strider reaches its prey it forces its sucking mouthpart through a joint or kink in the prey’s exoskeleton and uses it saliva tube to inject various chemicals into the prey that paralyzes its nervous system and liquefies its flesh, making it easier to sucks. A large insect will attract a bunch of water striders, pushing and jostling like lions or hyenas feeding on a fallen wildebeest.

Some predatory water bugs such as water scorpions have a long attachment running to their abdomen, which functions like a snorkel and allows them to remain submerged while they lay in wait for prey.

Katydids, Crickets and Grasshoppers

Crickets, grasshoppers cicadas and katydids make sounds. Since most insects are deaf this means they have to have ears to hear their sounds. Crickets and katydids make their sound by rubbing their wings together. Grasshoppers make their sound by sawing a strengthened vein on their wings against notched edges on their hind legs.

Crickets chirp at rates of 4 or 5 times a second to more than 200 times a second. Crickets chirp faster when the weather is hot, with the rate varying from species to species. One species, the snowy tree cricket chirps so reliably a formula called Dolbear’s Law (named after A.E. Dolbear, who reported the finding in 1897) produces a temperature gauge. Count the number of chirps in 15 second and add 40 and you get the temperature in Fahrenheit.

Katydids flourish in humid, tropical regions around the world and are particularly numerous in rain forests. Some are brightly colored to warn predators than an unappealing meals awaits them if they take a bite. Other avoid trouble by disguising themselves as leaves or lichens.

Grasshoppers have wings but don’t fly very well. The first segment, or femur, of the hind leg is long and wide, containing powerful muscles that can launch the insect to their spectacular jumps, with their wings used to extend their flights. On the second segment, or tibia, of the hind leg are a line of nasty barb that help defends the insects from attack from behind. Birds such as crows that regularly feed on grasshoppers have dense tufts of hair that thick out from the bases of their beaks that help protect their eyes.

Cockroaches are among the oldest creatures still on the earth. They first appeared about 300 million years ago.

Locusts, See Deserts


Cicadas are the noisiest of all insects, They make their sound by vibrating tiny membranes called tymbals that are snapped in and out by powerful muscles that can move back and forth 600 times a second. The sound is amplified in a large empty resonating chamber then forced through flaps. Males sing to define their territory to potential male rivals and to attract females.

Cicadas hear with circular eardrums on either side of their thorax. Many cicadas are large and fearsome looking by the they don’t bite or sting. They generally live a relatively short life in their adult form. The spend most of the life underground sucking on roots.

Cicadas spend nearly their entire lives under ground. They come to the surface for a few frantic weeks of mating before using up their strength and dying, often signaling summer is coming to an end.

In many species of cicada females lay their eggs in slots which they cut into tree twigs. When the eggs hatch they drop down to earth where the larvae quickly burrow into the ground. The larvae feed on tree roots and take a long time to grow. The smaller species are ready to come to the surface in two or three years but the large ones take five to seven or even longer. The 17-year locusts (a kind of cicada) are the most famous of these.


The first fleas appeared around 50 million years ago. Today there are about 2,000 different species. The male sex organ of some flea species is a complex device that takes up a third of the male’s body and contains spines, lobes and tickling devise that resembles a feather duster. Inside the females body it must follow a meandering route with many wrong turns to the place where sperm is deposited. Penetration can take up to 10 minutes and copulation can last between three and nine hours.

Flea jumps of 34 inches has been recorded. If a fleas' jumping skill were transferred to a human that human would be able to leap over the Statue of Liberty a 600mph continuously for three days straight. Their incredible strength and jumping ability explains why they were recruited for flea circuses.

To hop, fleas use a devise based in a structure in their flanks that once served as a hinge for their ancestors wings and is made from an elastic substance called resilin. When a flea gets ready to jump the resilin is slowly compressed and then locked into position. When it is released it produces an audible click and straightens the flea’s leg with an incredible amount force.

Image Sources:

Text Sources: Mostly National Geographic articles. Also “Life on Earth” by David Attenborough (Princeton University Press), New York Times, Washington Post, Los Angeles Times, Smithsonian magazine, Natural History magazine, Discover magazine, Times of London, The New Yorker, Time, Newsweek, Reuters, AP, AFP, Lonely Planet Guides, Compton’s Encyclopedia and various books and other publications.

Last updated March 2011

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