CHAPTER ONE Incredible Insects Insects are the most varied of all invertebrates animals without backbones and are essential to life on Earth They pollinate fruit trees and break down dead plants and animals to make soil Other animals eat insects as a vital part of their diets There are more than one million known insect species crawling swimming and flying in environments from tropical rain forests and deserts to rivers and swamps as well as in backyards and bedrooms all over the planet But there could be at least two million insect species still unidentified Insects range from beautiful dragonflies and butterflies to scavenging ants and fruit flies but they all share the same characteristics They have an external skeleton or exoskeleton Bumblebees spread pollen from flower to flower enabling plants to reproduce
Scientists have found many trilobite fossils three pairs of legs a segmented body including a head thorax and abdomen and one pair of antennae Most adult insects also have wings BEFORE BUGS Half a billion years ago there were no insects Planet Earth looked very different On land there were no animals Nothing flew in the sky No trees flowers or grass grew But in the ocean life was abundant Algae floated on the ocean surface providing food for the marine life below Strange creatures called trilobites looked like giant pill bugs They lurked on the muddy seafloor
in the shallow water alongside sea snails starfish and sea urchins Massive eurypterids or sea scorpions grew up to six feet 2 m long and terrorized the sea Eurypterids hunted for prey by grabbing it with their powerful claws They were the top of the food chain in a world where there were no vertebrates animals with backbones to compete with The period of life on Earth when these animals evolved beginning approximately 541 million years ago MYA is called the Cambrian explosion Prior to the explosion there were no animals with legs or eyes There were no predators Primitive multicelled organisms floated through the water passively absorbing nutrients Scientists studying oxygen levels in prehistoric rocks believe there may have been a small increase CAMBRIAN EXPLOSION Life on Earth began 3.8 billion years ago when the first molecules capable of replication developed But it wasn't until the Cambrian explosion 541 MYA that life took off It's described as an explosion because many new species of animals evolved in a relatively short period of time But despite its name this evolution didn't happen in a flash The Cambrian explosion lasted ten million years Because many fossils have been discovered from this period of time scientists believe there was an evolutionary explosion Before this period the fossil record was sparse Fossils found in the Burgess Shale a fossil deposit in what is now British Columbia Canada from 505 MYA show creatures recognizable as arthropods and worms So a rapid period of evolution must have occurred by then The Burgess Shale used to be 670 feet 200 m underwater The deposit formed 515 MYA when underwater mudslides swept creatures over a cliff and instantly buried them creating fossils As well as preserving hard shelled arthropods the rapid burial preserved soft bodied creatures that usually decomposed
