Springtails are small, soil-dwelling animals that look and act like insects but which some scientists separate from the true insects. Springtails have six legs and are therefore classed in the superclass Hexapoda. They used to be an order of the arthropod class Insecta but are now considered to be a full class of their own: Class Collembola. They have been separated from the insects because their mouthparts are enclosed in a cavity formed by the sides of the head, something that is not seen in true insects. They also have muscles in their antennae, a most un-insect-like characteristic. Another significant difference between springtails and true insects is that springtails do not have wings.
Springtails are small. Most are from 3 to 5 mm long at most. For this reason most people don't notice them, but they do have one interesting characteristic. The approximately 5000 species of springtails get their common name because of a forked tail on the fourth segment of their abdomens. This is known as a furca and it is attached to an appendage called a retinaculum on segment three. When it is released, it springs downward with enough force to launch the insect into the air. It is an effective way for springtails to escape predators. This can be seen by turning over rocks and rotting logs. When the springtails underneath are suddenly exposed to the environment, most of them will spring in all directions. This works for them the way flying works for many insects.
Springtails are saprophages, eating dead organic matter, or herbivores, grazing on living plants with their chewing mouthparts. A few are pests of such crops as mushrooms, sugar cane and tobacco. They can be quite abundant with as many as a million individuals occurring in an acre of soil. For this reason they are important members of the soil fauna, contributing to the turnover of organic matter and the production of new soil. This is particularly true in the soils of the far north, both tundra and taiga, where earthworms do not flourish. In these soils, most of the work of soil turnover is done by collembolans and nematode worms.
As well as in soil, springtails can be found in other damp places such as rotting vegetation and among mosses. Some also live on the surfaces of pools, both fresh and salt water. They have a ventral tube on the first abdominal segment which can be used to take up and hold water. It is also used by aquatic species to grip the water meniscus and thus float on the surface. They do not have a solid shell and can lose water through their body surface so they are restricted to damp environments. One common name is snow flea because they may be seen on the snow in northern and alpine climates.
Their life cycle is simple. They mate and the females lay eggs which hatch into immatures that moult several times before achieving sexual maturity. Unlike most insects, they continue to moult and grow throughout their adult lives.
Springtails come in a variety of colous, although most are grey or white. Yellow is not uncommon, but my favourites when I was studying tundra soil collembola were pink sminthurid springtails. With their large black eyes, bent antennae and fat pink bodies, they resembled stuffed toys more than living insects. They even come in purple. Why they are so colored is not immediately obvious, since they live in the dark and their eyes are very simple. This is just one of many things that we do not know about these obscure but beautiful little creatures.
For more information: http://www.collembola.org/ http://www.cals.ncsu.edu/course/ent425/compendium/collem.html