Some people cringe at the sight of them, other people love to pick them up and study them. Insects are everywhere. In fact, insects are the most numerous creatures on the earth. They live on all of the continents of the world except Antarctica, although a few may have hitchhiked there with human scientists who have gone to study the area.
The scientific name for insects is Heteroptera. It is estimated that there are over a million different species of insects on the earth. Insects compose over 80% of the world's animal population. And within each species there are literally millions of members. New insects are being discovered all of the time. In fact, scientists believe that there are more species we don't know about yet, than we currently have identified. That's really amazing to think about!!
The study of insects is known as entomology. You would think all those entomologists could give a more accurate count of the number of insects on the earth. But counting insects is more or less impossible. The truth is, most insects hide – that is one of the ways that they protect themselves. Many live underground or inside trees and other living things. Lots of them have very short life spans – maybe a few days. This makes it hard to count them. So scientists make estimates based on colonies found in a given area or evidence insects leave behind.
Insects do not have bones like you, but instead have a hard outer covering known as an exoskeleton. This exoskeleton protects their organs and gives them support for moving around. Their bodies are divided into three sections: the head, the thorax and the abdomen.
HEAD: The head is where you will find the eyes and mouth. The eyes of insects are much different than those we use to see. An insect has what is called a compound eye. While a human eye has just one lens for sight, the insect's eye is covered in lots of lenses which allows them to see in a wider span around their head. These eyes provide multiple images made up of dots – much the same way as a television works. They don't “see” well, but rely on movement or distance for identifying objects.
The mouth of insects can be one of two forms, depending on the insect. Some have a mouth shaped like a straw called a proboscis that allows them to suck nectar from flowers. Butterflies have this type of mouth. Mosquitos have a variation of this type of mouth which also allows for piercing the skin of a victim to suck out blood.
Other insects have chewing mouths for eating leaves or bark. Ants and termites are perfect examples of chewing insects. The chewing mouths can, in some insects, be used for tearing or cutting – they can even use them as tools to build.
Instead of a nose for smelling like we have, insects have antennae on the tops of their heads. These antennae do the same job our nose can do, but even better. It can help them tell temperature, locate food, identify egg laying locations, avoid pesticide, and even find companions. The antennae can even be used for hearing or taste in some species of insect. The antennae can be moved around by muscles in order to point them for a clearer understanding.
Thorax: Insects are identifiable by their six legs which are attached to the thorax. If they have more than six legs, they are not insects. The legs are jointed just as yours are but have a claw at the end where your foot would be. The claw is used for grabbing and holding things. Some insects have a special pad near their claws that is covered in very fine hairs. This is used for climbing up surfaces that are vertical or smooth like windows and walls. In some insects, such as grasshoppers, the back legs are larger and stronger for hopping. The praying mantis has larger front legs which fold forward and give them the appearance of praying. Some insects can use their legs for digging, grabbing or carrying food or materials to create shelter. Some can even swim.
Insects fall into two categories; those with wings such as mosquitoes and flies, and those without wings like ants and beetles. The wings, like the legs, are also attached to the thorax. Depending upon the insect, they can have two pairs of wings. Some wings are hard, similar to the exoskeleton or leather like. These hard wings are not used for flying but are used for protecting the softer, paper-like wings. Insects with two sets of wings are known as “true bugs.” While we might call all insects bugs, only those with this distinct second set of wings actually qualify.
Abdomen: The abdomen contains all of the internal organs for digestion, breathing and reproduction. Insects actually breathe through the sides of their abdomen. Their blood carries food but not oxygen so their respiratory and circulatory system is different than humans. Insects' blood is not red, but usually clear or variations of yellow to green.
Insects go through changes during their lives known as metamorphosis. In the insect world, there are two different forms of metamorphosis; simple and complete. Different kinds of insects live different metamorphic stages.
Egg ➲ Nymph ➲ Adult
An adult insect lays eggs. The eggs hatch and the resulting life is known as a nymph. Because the outer skin or exoskeleton is hard, they must shed this layer in order to make room for the new sized body as they grow. During each phase of growth they are known as an instar. When the nymph can grow no larger it is known as an adult. Nymphs and adults eat the exact same food and have similar physical shape and coloring. Once they become an adult they are then capable of laying eggs and the cycle repeats. Grasshoppers and crickets are examples of insects that go through simple metamorphosis.
Egg ➲ Larva ➲ Pupa ➲ Adult
An adult insect lays eggs in this version of metamorphosis, also. This is where the similarities end. The eggs hatch to reveal the larva. Larvae are fairly formless no matter the species. In the case of butterflies they are called caterpillars - wormlike creatures that do nothing but eat. Flies' larvae are also shaped similarly, but are small, white and have no identifying marks. The larvae do not eat the same food as the adult. In fact, some insects stop eating once they have passed the larva stage. As the larvae grow, they shed their outer exoskeleton several times.
At some point the larva knows to begin a process of becoming a pupa. In this stage, a caterpillar will suspend itself from a branch or other sturdy support and begin to cover itself in a protective covering. Some insects, like bees, have a special place provided for them by the colony to cover themselves up. This is known as a chrysalis or a cocoon. From the outside it looks as if nothing is happening. But, inside the cocoon, a complete change is happening. The parts of the larva are rearranging – the organs, the muscles, and other body parts are developing into a completely different creature. When the time comes for the adult to appear, which can take from days up to years depending on the species, it will fight its way from the chrysalis or cocoon and what emerges is the adult. Butterflies and bees goes through complete metamorphosis.
Check Science Trek's site on Butterflies to learn more about complete metamorphosis.
Insects are Important
Sometimes we are annoyed by insects who bite us or fly in our face when we are trying to picnic. But they are more than a nuisance. They are a vital part of our environment.
Without insects to crawl around in flowers as they hunt for their food, we would be without much of our own food. Some insects accidently gather pollen, which is a dusty material made inside the flower, onto their legs while they move inside of the flowers. Then, when they visit the next flower, this pollen is rubbed off to fertilize and create the mechanism that allows a plant to create fruits or vegetables. This is known as pollination.
In addition to helping to create food for us, they also work to rid us of dead plants and animals. Some species of insect are the key to keeping us from being knee deep in dead matter. When a plant or an animal dies, insects, bacteria other animals sweep in to eat the remains and turn it into soil through their digestive process. This is the original version of recycling.
Some insects spin a material known as silk which can be woven into fabric. It is considered to be a very valuable material and is used in the making of lots of clothing.
While there are insects that can be pests and cause the human world issues, there are also insects who eat the pests. Some gardeners purposely buy lady bugs to live in their garden and eat pesky insects that would otherwise eat the plants in the garden.
Let's face it, insects can be food for some of our favorite animals. Birds, fish, frogs and snakes dine on insects all of the time. This is just part of the natural cycle of things. In some parts of the world, humans enjoy snacking on insects too.
Here are some facts about insects that you may not know.
Houseflies find sugar with their feet
Ants can lift 50 times their own weight at one time
Only female mosquitoes bite
The queen termite can live for 50 years
All insects have 6 legs – if they have 8 they are spiders
Termites will communicate with other termites by banging their heads against wood
Katydids and walking stick insects camouflage themselves by looking like leaves and branches
Some insects can survive being frozen and thawed out again