Springtails (Collembola) form the largest of the three lineages of modern hexapods that are no longer considered insects (the other two are the Protura and Diplura). The three orders are sometimes grouped together in a class called Entognatha because they have internal mouthparts, but they do not appear to be more closely related to one another than to insects, which have external mouthparts.

Some DNA sequence studies suggest that Collembola are a separate evolutionary line from the other Hexapoda, but others disagree; this seems to be caused by wildly divergent patterns of molecular evolution among the arthropods. Consequently the taxonomic rank of springtails has changed according to need: when they were included with the insects, they were ranked as an order; as part of the Entognatha, they are ranked as a subclass. If they are considered a basal lineage of Hexapoda, they are elevated to full class status.

Various sources and publications have suggested that some springtails may parasitize humans, but this is entirely inconsistent with their biology, and no such phenomenon has ever been scientifically confirmed, though it has been documented that the scales or hairs from collembolans can cause irritation when rubbed onto the skin. They can sometimes be abundant indoors in damp places such as bathrooms and basements, and under such circumstances may be found on one's person, but this is only accidental.

Claims of persistent human skin infection by springtails may indicate a neurological problem, or else delusory parasitosis, a psychological rather than entomological problem. Researchers themselves may be subject to psychological phenomena. For example, a publication in 2004 claiming that springtails had been found in skin samples was later determined to be a case of pareidolia; that is, no springtail specimens were actually recovered, but the researchers had digitally enhanced photos of sample debris to create images resembling small arthropod heads, which they then claimed to be springtail remnants. However, Hopkin reports one instance of an entomologist aspirating an Isotoma species and in the process accidentally inhaling some of their eggs, which hatched in his nasal cavity and made him quite ill until they were flushed out.

More serious and better documented than parasitoses on humans are the records of springtails as pests for some agricultural crops. Sminthurus viridis, the 'lucerne flea', has been shown to cause severe damage to agricultural crops and is considered as a pest in Australia. Also Onychiuridae are known to feed on tubers and to damage them to some extent. However, by their capacity to carry spores of mycorrhizal fungi and mycorrhiza-helper bacteria on their tegument, soil springtails play a positive role in the establishment of plant-fungal symbioses and thus are beneficial to agriculture. They also contribute to control plant fungal diseases through their active consumption of mycelia and spores of damping-off and pathogenic fungi. It has been suggested that they could be reared to be used for the control of pathogenic fungi in greenhouses and other indoor cultures.

Content Resource : http://en.wikipedia.org/wiki/Springtail