THE SPRINGTAILS (COLLEMBOLA) OF
R. A. Cannings and G. G. E. Scudder
Copyright © 2005 - All rights reserved
About 7000 species of Collembola are named worldwide, but because of their small size and hidden habits, thousands more certainly exist. The Canadian Collembola fauna has been estimated at about 520 species. There are 18 families recorded in B.C., including 64 genera and about 270 species, but probably 400 species live in the province. Nine species are recorded only from B.C., but further collecting elsewhere may reduce this number. There is much need for more work on these important organisms.
The earliest fossils of Collembola date to the Devonian Period, almost 400 million years ago, making the springtails among the earliest recorded terrestrial animals. They live mostly in soil (some as deep as 1.5 metres) or the leaf litter, but many live deep in caves, high in trees or on the surface of water; on icefields, the marine intertidal zone, or in termite nests. They flourish in deserts, on arctic islands, in the Himalaya Mountains to almost 7800 metres and in Antarctica at almost 85ºS latitude. Springtails feed mostly on fungi, dead and decaying plants, bacteria, algae and spores. Mostly the mouthparts are cutting and crushing, but in some families they are piercing and sucking. Some springtails are predators, feeding on nematodes, rotifers and even other Collembola. The order is famous for swarming; incredible numbers can appear on snow or other bare places. Average densities of springtails in the soil are around 100,000 per cubic metre, but extremes of 100 million per square metre are reported.
Mating strategies vary. Males produce spermatophores, often on stalks, and either deposit them at random for females to discover, or indulge in more sophisticated courtship activities to transfer sperm. Mating displays reach their zenith in the Sminthurididae and Bourletiellidae where males have modified antennae that clasp the female during mating and females may carry the smaller males, sometimes for days. Females lay eggs singly or in batches in the soil or leaf litter. Some springtails are parthenogenetic.
Maturity is reached in three to twelve moults, but moulting continues throughout life and up to 50 are recorded. All species alternate a feeding, non-reproductive stadium with a reproductive one, and female appearance may change markedly with the moult between these two functional stages. Collembola, especially in the Hypogastruridae and Isotomidae, are well known for ecomorphosis, a phenomenon where certain life stages are characterized by reduced activity and distinct morphological change. These may be caused by extreme climatic events such as drought or may merely be changes that come and go with the seasons. The most obvious morphological shifts include changes in the type, size and position of setae and spines, the shape of the mouthparts and furcula, and the loss of secondary sexual characters.
Springtails are one of the most widespread and abundant groups of terrestrial arthropods. Their evolutionary history and position in the classification of the arthropods are debated, but here we consider them separate from the Class Insecta in the Class Parainsecta, Order Collembola along with the Order Protura. Together with the Class Diplura, the Parainsecta constitutes the entognathous hexapods. The relationships of these classes with the Class Insecta are mostly unresolved. The presence of antennae and the absence of cerci separate springtails from the Protura (both antennae and cerci absent) and Diplura (antennae and cerci present); as the classification indicates, Collembola are considered more closely related to the Protura than to the Diplura.
Springtails are minute to small, usually 1 to 5 mm long (range of adults is from 0.2 mm to 10 mm ). They can be colourless or colourful, pigmented in patterns of yellows, red, brown, purple or black. In the more primitive orders, the body is divided into a distinct head, a thorax with three segments and an abdomen with six segments. In more derived groups, the body is globular, because of the expansion of the thoracic segments or the fusion and enlargement of the abdominal segments. The antennae have four segments, all individually muscled (insects have only the first three segments with muscles); some segments may be subdivided. Each eye is made up of a maximum of eight simple eyes; many species are blind. The mouthparts are similar to those of insects, but the mandibles and maxillae are hidden by, and the labium is fused to, enclosing folds of the head capsule. The variations on mouthpart structure are important in classification.
The abdomen is peculiar; it has only six segments, which bear three unique structures, the collophore (ventral tube), tenaculum and furca. Only the collophore occurs in all Collembola, and it gives the order its scientific name. It consists of a tube with eversible sacs at the tip; these are derived from a pair of appendages on segment 1. Apparently the collophore is important in fluid balance; it also is the source of grooming fluids and can also function as a sticky appendage to adhere the springtail to smooth surfaces. In some species the tube may be twice as long as the body. The furcula is a jumping organ that evolved as an aid to escaping predators; it is derived from the basal fusion of paired appendages on segment 4. The tenaculum is the catch for the furcula on segment 2. Working together, these organs can propel the animal many times its length. Species living in the soil normally have a reduced furcula and many species have actually lost it. There are three pairs of walking legs; There is only one leg segment, the tibiotarsus, below the femur.
Bellinger, P.F., K.A. Christiansen and F. Janssens. 2002. Checklist of the Collembola of the world. http://www.collembola.org
Christiansen, K.A. 1964.The bionomics of the Collembola. Annual Review of Entomology 9: 147-178.
Christiansen, K.A. and P. Bellinger. 1998. The Collembola of North America, North of the Rio Grande. Second edition. Grinell College, Grinell, Iowa. 1518 pp.
Hopkin, S.P. 1997. Biology of the springtails (Insecta: Collembola). Oxford University Press, Oxford. 330 pp.