Insects make up over half of Earth’s animal biodiversity, with over one million species described and estimates of up to 10 million. They have hard exoskeletons, three body sections, and a variety of diets. Some are social and build nests, while others are solitary.
Insects are a large group of arthropods (segmented animals) that make up more than half of the animal biodiversity on Earth. Over one million species have been described, with recent estimates of the total number of species ranging as high as 10 million. Only about one million non-insect animal species have been described. Common insect species include dragonfly, praying mantis, grasshopper, butterfly, moth, fly, true bugs, beetles, bees, wasps, and ants. Insects have been around since at least the Devonian Period, about 400 million years ago, when the first vascular plants appeared on earth. Insects are primarily terrestrial: their close relatives, crustaceans, are better adapted to seas.
Like other arthropods, insects have hard exoskeletons that protect them from attack and desiccation. They tend to be small, less than a couple of centimeters, up to 0.139 mm (0.00547 inch, fairy) and 55.5 cm (21.9 inch, stick insect). The largest known insect that ever lived is Meganeura monyi, a prehistoric relative of a dragonfly with a wingspan of over 75 cm (2.5 ft).
Insects have three main body sections; a head, thorax and abdomen. The head has compound eyes, sensory antennae, and modified appendages that serve as mouthparts. The abdomen contains the majority of organs. Insects lack both lungs and a closed circulatory system. The exchange of oxygen takes place through the trachea and direct diffusion with the outside. The “blood” of insects is called hemolyph. The hemolyph distributes oxygen to organs by simply washing them, rather than using blood vessels, as in mammals.
Insects have a variety of diets. Most are scavengers, consuming dead plant and animal material or dung. Others, like bees, survive on the nectar of flowers. Some are insectivores, eating other insects. Still others are parasites, some even capable of digging into the brains of other insects and controlling their movements. Some insects possess toxins that they can deliver to prey through a sting or even surface contact.
Most insect species rarely interact unless they are mating or competing for mates. Some, however, are particularly social, such as wasps, bees and ants, all of which build nests or burrows. These species have “queen” variants capable of reproducing, while the others act as “workers”, defend the nest and collect food.
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