Insects: Evolution, Successful Group, & General Characteristics of Insects


The study of insects is called entomology; the word which is derived from Greek “Entoma” meaning cut into. Insects are the most diverse organisms on Earth. Insects are the group of phylum Arthropoda.

Like all arthropods, insects also have exoskeletons made of chitin, body divided into segments and protected with cuticle. They have open blood circulatory system with organs openly bathed in a fluid called hemolymph.

Body segmentation means the division of body externally into different regions and the process termed as tagmosis. The beautiful colors of insects are due to pigments in exocuticle such as melanin.


Insects come from the phylum Arthropoda. Arthropods are characterized by having the following functions: a hard external skeleton (called an exoskeleton), a segmented body, at least 3 sets of jointed legs. The Arthropoda is divided into a number of classes. These consist of the:

  • Crustacea (crabs, crayfish, prawns).
  • Arachnida (spiders, mites, scorpions).
  • Myriapoda (millipedes & centipedes).
  • Insecta (insects)

Insects are the most extensively dispersed and the most various of all animals. They can be found in the oceans, on polar ice caps and flying over the Mountain ranges and living in steaming hot volcanic springs. According to one computation, there are about 1,000, 000, 000,000,000,000,000 (one million trillion) insects in the earth, more than a billion for every single person.

Of the 2 million approximately known species of plants and animals about 700,000 of them are insects. New insects are found and named at a rate of about 2,000 a year. Thousands– possibly millions to be discovered. In regards to weight, insects account approximately 85 percent of all animal life types, All the world’s insect weighs more than 12 times all the world’s individuals.

Evolution of Insects


Insects are an ancient group of animals. The very first insects probably appeared before the Devonian duration (400 – 360 million years ago) and by the Carboniferous duration (360 – 285 million years ago) had taken to the air.

Adaptation to flight showed a highly effective method and throughout the Permian period (285 – 245 million years ago) insects attained their biggest variety. No other arthropod group has attained flight. By the Permian, the basic physical structure of many of the modern-day orders of insects had developed.

The more recently progressed Hymenoptera (ants, bees, wasps and sawflies) and Lepidoptera (butterflies and moths) appear as fossils in the Jurassic duration (210 – 145 million years ago). The Mantodea (hoping mantids) appeared in Eocene duration in fossilized amber (60 – 35 million years ago).

The Successful Group

The insects are the most effective arthropods. There are even more species in the class Insecta than in any other group of animals. These remarkably diverse animals have actually dominated all the environments on earth except for the frozen polar environments at the greatest elevations and in the instant vicinity of active volcanoes. Insects are the only invertebrates (animals without a backbone) with wings.

Much of their success results from their capability to fly and colonize new habitats. An easy escape from enemies. They can quickly disperse to new environments. Can exist in extremely little spaces and specific niches.

They Produce a large number of offspring relatively very quickly. The genetic variety and great potential for adaptation to new or changing environments are likewise essential elements which made insects the most successful group on the Earth.

General Characteristics of Insects

No matter their size, behaviour or habitat, insects worldwide have common physical attributes.


The exoskeleton

Insects have an external skeleton called an exoskeleton. This hard covering secures and supports the body. It is made up of 2 layers. The outer layer is thin, waxy and water-resistant. The inner layer is much thicker and is made from chitin. Depending on the insect, the exoskeleton can be rather hard and rigid– like that of a cockroach or less so when the insect is in its larval (caterpillar) phase or if it has a soft body– like a blue blowfly.

The exoskeleton is non-living so it can not grow with the insect when it remains in its larval form or as a grownup. Insects shed their old exoskeletons, expand to a bigger size and then wait for the new exoskeleton to solidify. This is called moulting, and it occurs sometimes throughout an insect’s life expectancy. One of the most common signs of moulting comes in the spring when we find cicada shells (exoskeletons) on trees and fences.

The head

The head is the top section of an insect’s body. A number of the insect’s sense organs are found here. A set of antennae allow insects to smell, feel the surface area of an item, sense cold and hot, listen to noises or detect motion. Insects have a set of compound eyes– each made up of countless lenses.

Compound eyes offer a larger field of vision, which is truly beneficial for flight or when searching for prey. Insects might likewise have simple eyes called ocelli, which include single lenses. They enable insects to notice light and dark. The insect’s mouthparts are likewise on the head.

Insects have actually developed mouthparts for a variety of functions. Insects such as beetles and grasshoppers have mouthparts that permit them to chew. Butterflies and moths have a proboscis that permits them draw liquids. Insects like mosquitoes have mouthparts that pierce their food, while houseflies sponge their food, dissolving it in saliva before sucking it up.

The thorax

The thorax is an insect’s middle section. It includes three sections. Each section has a set of jointed legs. If the insect has wings, a pair of forewings and a set of hind wings are attached to the thorax. Like our native birds, Aotearoa New Zealand has a significant number of wingless or flightless insects. For instance, the honi/mole cricket is the only wingless mole cricket worldwide.

The abdomen

The abdomen is the rear or last section of the insect. This is where the digestive, excretory and reproductive organs lie. The abdomen has 9– 11 segments. Each segment has a pair of spiracles or openings in the exoskeleton. Insects open the spiracles to catch air in but close them to prevent water loss. Marine insects have comparable approaches to prevent water from entering the spiracles.

Development and Growth

Insects hatch from eggs as larvae or grub that often look like brief, stubby worms. They then become a pupa and finally metamorphose into a full-grown insect. As they grow they shed their old skins exoskeletons and grow new ones. Larvae and pupa spend much of their time eating. Unlike bird eggs, insect’s eggs include really little yoke or food. Rather the eggs are laid on or near food sources and the young start consuming as quickly as they hatch. The primary purpose of insects is to reproduce.


These are the features that can help us differentiate insects from other arthropods.