Arthropods, such as insects, shrimps, spiders, centipedes, crayfish, scorpions and millipedes, are the most diverse group of animals in the world. They can be seen on land, in the air and in the sea and are classified under the phylum Arthropoda. Many arthropods remain undiscovered, and the number of species in the largest arthropod class, insects, is assumed to be in the tens of millions.
Arthropods are invertebrate animals which have a hard skeleton, or exoskeleton, outside of their bodies. The exoskeleton is composed of segments and jointed appendages. Arthropods also have multiple pairs of limbs and bodies. Most arthropods possess these characteristics. They range in size from microscopic insects to large forms that grow up to several meters in size.
Arthropods are considered a major group of disease carriers and transmitters of infectious diseases. The most common are mosquitoes, flies, lice, ticks, fleas and bugs. Many species of arthropods are agricultural and forest pests and are responsible for some of the most devastating plagues and famine in the world. Bees and butterflies, however, greatly contribute to the human food supply through pollination. Bees also produce honey, which is the source of a growing industry and international trade.