Hexapoda - insects page 1, 2, 3, 4, 5

Insect general information is spread over a number of pages. This page is divided into 3 sections.
1. A list of the insect orders with a link to the main page for that order.
2. A list of topics relating to insects in general.
3. A very brief overview of the insects. Insects are in the Phylum Uniramia, and I've included links to pages in this phylum too.

List of general insect topics

Smith, L. (2014). Characteristics of the insect orders. Amazon. Characteristics of the insect orders with drawings and photographs to help you understand the differences between the different types of insect, and identify which order an insect is in, as well as fast facts about each insect order, and links to web pages with more detailed information. Many orders have separate sections about the life cycle of the insect as well as its habitat requirements, and fossil history.

"If all mankind were to disappear, the world would regenerate back to the rich state of equilibrium that existed 10, 000 years ago. If insects were to vanish, the environment would collapse into chaos." E. O. Wilson

Overview of the insects

There are over a million described species and many more waiting to be described and even more waiting to be discovered; some authorities say as many as 4 million insect species await discovery. In fact more than 50% of all described species (animal and plant) on earth are insects. In the UK there are around 24,000 species. In North America there are around 90,000 described species, but many more waiting official description (see the taxonomy page for more on this). They are in around 30 Orders, depending on which book you read. They range in size from less than 1 mm up to 20 cm in length.

Previously it was thought that the Myriapoda - Centipedes, Millipedes etc., were the closest living relative to the insects, but now some scientists believe that the Remipedia in the Crustacean Phylum are their closest living relatives. Both insects and Remipedia have similar brains, nervous systems and proteins.

The earliest fossil insects date back to 410 million years ago, but as these insects were already quite elaborate, the true origin may be much earlier, perhaps as early as 480 MYA in the Ordovician, around the same time as the earliest terrestrial plants. The insects around then were wingless and resembled modern springtails. Rhyniella precursor, a springtail found near Rhynie in N E Scotland dates from 410 MYA. The insects are thought to have started their colonisation of the land around 320 million years ago during the Carboniferous.

The secret of the success of the insects can be linked to the following features:

• Tagmosis allowing specialisation in each body area.
• Jointed appendages and striated muscles giving efficient locomotion.
• Exoskeleton which provides protection and prevents dehydration while still being flexible and light enough to allow movement. The main component of the exoskeleton is a carbohydrate called chitin. The hardening of the cuticle is a result of sclerotization, i.e. the bonding of protein molecules and their cross-links within and between the lamellae of the procuticle. This forms sclerotin, a resistant and insoluble protein. The muscles are attached to the inside of the exoskeleton (unlike ours which are attached to the outside of our skeleton).
• Complex musculature allowing rapid movement.
• Branched tracheae and tracheoles allowing direct passage of oxygen to the cells, so enabling a relatively high metabolic rate. The trachea end in spiracles which run down the sides of the abdomen and thorax. Diagram of the tracheae of a flea
• Complex sensory organs of vision, chemoreception, hearing and touch; all enhancing awareness of surroundings.
• Complex behaviour patterns leading to social organisation in some.
• Metamorphism reducing competition between individuals of different stages in the life cycle, e.g. caterpillar and butterfly occupy different niches.

About 85% of the world's flowering plants rely on insects for pollination, that includes about 35% of global crop production.