The group of Arthopoda are the most numerous animals on Earth: until today more than a million species of insects and other arthropoda have been classified, while the number of living insects today can reach a billion of billions. Arthropoda can be found in all habitats, and it was calculated that in a mild region there can be 20 million arthropoda distributed in the biosphere.
The word “insect” comes from the Latin insectum, which means “cut”; the body of these invertebrates is actually divided into segments that are neatly separated from each other. The class Insects is composed of approximately 1,000,000 species, divided into 28 orders, including: Lepidoptera (for instance the butterfly and the moth;  Coleoptera (such as the ladybird), Diptera (such as the fly), Hymenoptera (such as the bee, the asp and the ant), Orthoptera (such as the grasshopper). They are also called “Hexapoda” which in Greek means “six feet”, since all Insects have six limbs.
They have an external skeleton called “exoskeleton”: as it grows, the insect peels off its old external coating while a new one is ready underneath. Generally, the males and females of one species are very different from each other in both size and shape (sexual dimorphism). Fertilisation is internal and the females produce eggs from which larvae will be borne. For some species, there is the metamorphosis: the larva pupates inside the cocoon, which it will leave when completely mature.

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