Insects

Did you know that there are many more kinds of insects on earth than any other kind of living creature? It's hard to imagine, but 95% of all the animal species on the earth are insects! Millions of insects can exist in a single acre of land! Over one million species have been discovered by scientists, and they think that there might be ten times that many that haven't been named yet!

They are divided up into 32 orders, or groups of insects. The largest order is the beetles (Coleoptera) with 125 different families and around 500,000 different species. In fact, one out of every four animals on earth is a beetle. Scientists estimate that 10% of the animal biomass of the world is ants, and another 10% is termites. This means that 'social insects' probably make up an incredible 20% of the total animal biomass of this planet!

Insects eat more plants than all the other creatures on earth! They are also so important in the breakdown of plant and animal matter, that without them, we would have a world covered with dead plants and animals! In addition to all of this, insects are a major food source for many other animals.

Insects are incredibly adaptable creatures and have evolved to live successfully in most environments on earth, including deserts and even the Antarctic. The only place where insects are not commonly found is in the oceans. Insects have an amazing number of differences in size, shape, and behavior, but they all have 4 characteristics in common.

All insects must have:

• three body parts - a head, thorax, and abdomen
• six jointed legs
• two antennae to sense the world around them
• an exoskeleton (outside skeleton)

If all four of these things are not true, then the animal can't be called an insect! Spiders are not insects because they have eight legs and don't have three body parts. Centipedes and millipedes have way too many legs to be called insects! Most insects have one or two pairs of wings, but wings aren't necessary to be classified as an insect.

Scientists believe that insects are so successful because:

• they have a protective shell or exoskeleton
• they are small
• most of them can fly.

Their small size and ability to fly helps them to escape from enemies and travel to new environments. Because they are small they need only small amounts of food and can live in very small cracks and spaces. Insects can also produce large numbers of offspring very quickly.

Insect Reproduction

Most species of insects have males and females that mate and reproduce sexually. Sometimes there aren't many males or they are only around at certain times of the year. When there aren't any males, females of some species may still reproduce! This is common, particularly among aphids.

In many species of wasps, unfertilized eggs become males, while fertilized eggs become females. In a few species, females produce only females.

Insects may reproduce by laying eggs, or in some species, the eggs hatch inside the female and are born a short time later. Sometimes in aphids, the eggs hatch inside the female and the young aphids remain inside the female for quite a while before birth.

Insect Growth and Development (Metamorphosis)
Insects usually go through four separate life stages: egg, larva or nymph, pupa, and adult. Eggs are laid one at a time or in masses, in or on plants, or even inside another insect! Eventually a larva or nymph emerges from the egg. There are usually several larval or nymphal stages, called instars. During each stage the nymph grows larger and molts, or sheds its outer skin before the next stage. They grow the most during the last one or two instars, or stages. All the growing happens during the larval or nymphal stages. The eggs, pupae, and adults don't grow in size.

The two types of metamorphosis typical of insects are incomplete metamorphosis (egg --> nymph --> adult) and complete metamorphosis(egg --> larva --> pupa --> adult).

Insects are cold-blooded, so the rate at which they grow and develop depends on the temperature of their environment. Cooler temperatures cause slow growth; higher temperatures speed up the growing process. If a season is hot, more generations, or life cycles, might happen than during a cool season.

Insect classification and identification

It is necessary to classify insects so that we can organize what we know about them and understand their relationships with other insects. For example, all members of a particular species will feed on similar foods, have similar developmental characteristics, and exist in similar environments. Most often, insect species are classified based on similarities in appearance (morphology). The flies, for example, can be distinguished and classified separately from all other winged insects because they have only one pair of wings.