Beetles occur throughout the forests, and hundreds of species have been found on tropical rainforest trees. Some species damage trees, while many are beneficial. Photo by Maya Walters.

Dinosaurs became extinct around 65 million years ago, but insects have survived on earth for over 300 million years. Millions of species of these tiny creatures exist, and neither dinosaurs or humans could have lived without them. For every individual person alive today, there are about 200 million individual insects, and if they were to suddenly vanish from the earth, humans could not survive more than a few weeks.

An insect's skeleton is on the outside of its body, and forms a hard protective shell. This "exoskeleton" is made out of a tough, solid substance called chitin, which is both strong and lightweight. Each insect's exoskeleton can contain chitin of different forms. Some is very rigid, and forms thick, solid structures and sharp cutting edges of claws or mandibles*. In other areas, the chitin can be thin and flexible. The huge variety in insect forms shows that chitin can be made into a limitless variety of shapes. There is, however, an upper limit on the size of an insect: past a certain size, the exoskeleton simply can't provide enough support, without being so thick that no room would remain for internal organs!

Below: A dragonfly. Below left: Portrait of a grasshopper. Photos by Maya Walters The first winged insects lived over 300 million years ago and some looked very similar to today's dragonflies -- only much larger! The oldest known fossilized dragonfly had a wingspan of 20 cm (8 in), and the largest fossilized dragonfly was found in the United States, with a wingspan of 60 cm (24 in)! The smallest insects are even smaller than some single-celled organisms. The largest known insect is South America's Hercules beetle (Dynastes hercules), which is over twice as heavy as a mouse.

Insects are voracious eaters. They consume more animal flesh than lions, tigers, wolves, crocodiles, and alligators combined. The daily amount of food consumed by a single swarm of African desert locusts is greater than the amount eaten by New York's entire population of humans. 50% of all organic material produced by green plants is ultimately consumed by insects.

The patterns on the wings of butterflies are created by microscopic ridges on the wing "scales". Photo by Maya Walters.

Insects have achieved success with "diversity through specialization". Each of the countless species has its own particular individual shape, coloring, behavior and food sources, yet every one has the six legs and two antennae that make it an insect. Over a million species of insects have been formally described, but millions more are still unknown, with the greatest profusion occurring in the tropical rainforests. In these areas where life is so abundant, insects, and indeed other animals, are faced with great competition for their habitat niches. They either become highly specialized, adapting to make use of one specific food source, or they become generalists. The generalists take advantage of many different food sources and habitats, but with less efficiency than the specialists.

95% of all animal species are invertebrates, the group of creatures including insects, arthropods and mollusks. Over 1 million species of insects have been identified, and about 7000 new species are discovered every year. As many as 30 million species of these animals may exist only in tropical forests. On this page: Just three examples of the seemingly limitless variety among insects. Photos by Maya Walters.

When we hear the word "insect", we tend to think "pest". When insects are damaging a forest, we usually think that the best thing to do is get rid of them. Why have insects acquired their bad reputation, and what benefits do we actually get from them? find out more

The social insects have some of the most fascinating behaviors. Ants, termites, and some bees and wasps live in complex, highly organized colonies, with work divided among individuals with different specialties. Millions of individuals can belong to a single colony. The queens of these colonies are the only ones that lay eggs, and the workers are all offspring of the queens.

However, not all social insects have evolved such complex social organization. The simplest social relationship is that of a mother remaining with her offspring until they are mature, rather than laying her eggs in a suitable location and then leaving them on their own. This limited social behavior is found in several species of beetles and cockroaches.

Ants and termites have the strongest social behavior. Depending on the species, anywhere from under twenty to several million workers live together in these colonies, foraging for food, taking care of the queens and larva, constructing the nest, and defending the colony. There are usually several different groups ("castes") of workers, each specializing in a different activity. For example, some workers become larger and develop strong jaws, and these "soldiers" specialize in defending and protecting the rest of the colony.

Top: A winged queen ant (Lasius pallitarsus) about to fly and eventually begin a new nest. Most of the thousands of young queens that fly every year are eaten by birds within a few days. Above: Two worker red wood ants (Formica obscuriventris). These ants are very important for controlling pests in temperate forests, as they eat huge numbers of other insects every day. Photos by Maya Walters.

Each day, these enormous colonies of ants capture and consume thousands of other insects as prey. This makes them extremely important in controlling the populations of "pest" insects in a forest. Often when there is a severe outbreak of an insect that damages trees in a temperate forest, the areas around large red wood ant nests remain undamaged because the ants catch the harmful insects. In Europe, ants have actually been used for pest control, and their nests have been moved to areas where they will be needed most.

Super-specialization among insects is more common than great flexibility. In some cases, however, a specific adaptation that once benefited an insect can suddenly become a liability. Especially when humans are involved. The nocturnal birch moth, or common peppered moth (Biston betularia), normally has pale, speckled wings. It rests during the day on shaded branches and trunks of birch trees. Around Manchester, England, during the industrial revolution, the normally light-colored birch bark was blackened with soot from factories. Birds could now easily pick out the light-colored birch moths, which had once been well camouflaged. Very soon, a formerly rare, dark-colored variety of the same moth began to take over from the much more common light-winged individuals. Until the industrial revolution, the unusual, dark moths had always been at a disadvantage because of their visibility to predators. Now the conditions were reversed, and the light-colored moths became very rare.

Sudden changes in conditions, similar to what happened in the event described above, are extremely rare. But when they do occur, they are almost always associated with human actions. Biologists have given the term "industrial melanism" to this kind of sudden, necessary evolutionary change. Today, in some industrialized areas of the United States, almost 90% of the butterflies are melanic, and the landscape is less colorful because of it.

Left: butterflies drink nectar from flowers and aid in pollination. Below: a bug turns its back on the camera. Photos by Maya Walters.