Most invertebrates are insects, and the remaining invertebrates consist of worms, slugs and snails. Unlike arthropods these animals lack segmented legs and are generally soft bodied.
- they have basically three body parts i.e: head , thorax and abdomen.
- they have no lungs. they respire through their skin.
- they live in colonies .
- some are harmful for humans like termite, mosquitoes jelly fish and houseflies.
- they lay eggs and not babies
1.The head, which is designed for feeding and sensory purposes and consists of one pair of compound eyes and up to 3 simple eyes, 1 pair of antennae and mouthparts, which may be piercing, chewing or sucking types depending on the insect.
2.The thorax, which is designed and is made up of 3 segments with each carrying 1 pair of legs. In some adult insects the last two segments of the thorax may support a pair of wings depending on the species.
3.The abodmen, which is designed for reproduction. The abdomen is the largest and softest of the 3 body parts. The abdomen houses all the organs vital for insect survival such as respiration, digestion and reproduction.
Insects inhabit a diverse range of habitats, both terrestrial and aquatic and this is often reflected by the great diversity in their appearance. Most undergo some degree of change or metamorphosis during their life cycle and young may not have all of the adult insect features such as wings.
Some insects, such as silverfish show no change throughout their lifetime except for an increase in body size. While other insects such as bugs or grasshoppers go through gradual stages of development, each successive stage (or nymph) is slightly more developed than the previous one. For example wings begin to develop from small wing buds and grow larger with each moult.
Other insects such as moths or beetles are typical of insects that undergo a number of abrupt changes as they mature; egg - larvae - chrysalis/pupae - adult. In insects such as these, the wings develop inside the body and are visible only after the adult emerges from the pupal stage.