Fleas (order 'Siphonaptera') are one of the major groups of blood-sucking insects. They belong to holometabolic insects. Holometabolism is a feature characteristic also of 'Diptera', 'Lepidoptera', etc. Fleas form a separate well-differentiated order, although phylogenetically they are regarded to be closer to 'Diptera' and 'Mecoptera'. At present approximately 2000 species and subspecies of fleas are known.

Fleas are widely spread on all continents, Antarctica included. They occur on hosts and in their nests in all types of habitats from the equatorial deserts and tropical rainforests to the northernmost regions of Arctic tundra. In general in Eurasia as in other continents, the largest number of species and genera of fleas occur in several regions with temperate subtropical climate and predominance of mountain landscapes. The most numerous flea fauna is known for Eurasia

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