(Huge thanks are due to collembologists Dr. Penny Greenslade, Frans Janssens and all my photographer buddies on Flickr. Without their help with identifications, knowledge and inspiring conversations, I wouldn't have even started this website.)
Collembola are without doubt, my favourite animals. They're diverse, complex, often intensely colourful and incredibly endearing. And they've held my attention almost exclusively for the last five years. For an animal very often under 1mm big, that's quite some achievement.
The name 'Collembola' derives from the Greek for glue piston, named through early observations by John Lubbock in the nineteenth century of tiny animals anchoring themselves to a surface using their collaphore, a tube-like structure containing two eversible tubes, under their abdomen. While I've observed this action myself, used certainly as a stabilising force, its main uses, though the eversion of the two vesicles, are thought to be the regulation of the body's water balance and excretion.
Springtail, the common name, comes from the ability of many Collembola to spring away from trouble using an appendage called the furcula, held under tension beneath the abdomen.
Collembola share some attributes of insects, with a body divided into three parts, consisting of a head with antennae, a three-segmented thorax, each segment having a pair of jointed legs, and an abdomen. However they also differ from insects in that Collembola are all soft bodied, lacking wings, have simple eyes more like crustaceans and have internal mouthparts.
Change is something that many collembolans are very good at. In a stressed environment, they are able to shrink their body size and change their shape rapidly as a coping strategy, within the space of one moult. The females can change the amount and size of the eggs that she lays, too, guided by environmental factors.
Living in the dark of caves, or deep in the soil layers inevitably leads to a whole set of adaptions. Pigments get discarded, antennae change length and the amount of tiny ocelli on the eyepatches reduce in number or disappear entirely.
And they slow down. Cave Collembola usually subsist on very little. They can't afford to waste energy running around so they often slow down. In an energy-poor environment, each small saving made to their energy usage aids survival.
In the case of the larger animals, size gets to a point where it begins to negatively impact on the effectiveness of jumping. So after millions of years of trying to jump and presumably just flopping about ineffectually, the furca atrophied in those species.
Not only the largest Collembola have lost their furcas. Environmental factors also influence such a change. Most of the soil-dwelling Collembola, like the Onychiuridae and Tullbergiidae, have also lost the ability to jump. However, the members of Neelidae do still have a functioning furca, even though they live in the bottom layers of leaf litter and top layers of soil. Certainly for the tiny Megalothorax species, having the ability to jump away in a very cramped environment is still potentially possible and therefore has some worth.
Collembola are one of the most widely spread and numerous of all animals in the world. They live virtually everywhere. Car parks and city streets, in sand, up trees, on water, in houses, on plants. And in and around soil, of course. Wherever you go, looking with a hand-lens, there will most likely be a collembolan scampering away from you.
They're officially the deepest living land animal, with a new species, Plutomurus ortobalaganensis, found in Krubera-Veronja cave in the Western Caucacus at a depth of 1,980 metres (6,500 feet) below ground. It was tempted out using cheese.
Desoria species of Collembola happily live on the summit of Mount Everest, while another genus in Tasmania lives for certainly part of its life, underwater, eating crunchy diatoms.
Collembola are one of nature's ultimate niche fillers, able to find a way into almost any environment in the world, given time. And time is something they've had a lot of. In 1919 a fossil collembolan, Rhyniella praecursor was found in the Rhynie chert. The chert dates to around 410 million years old, meaning that collembolans were one of the very first arthropods to become terrestrial.
Although until recently, they were grouped with insects, Collembola, along with Diplura and Protura are now thought to have followed some sort of parallel but not particularly linked evolution. But nothing is fixed. The fact is that things just don't fit comfortably into boxes, apart from cats. DNA bar-coding has certainly helped clarify some areas of confusion in the Insect/Entognatha situation while muddying many others.
Francesco Nardi et al published an influential paper in 'Science' in 2003, building on research from the USA and Japan. In it, they offered some of the first strong molecular and developmental evidence suggesting that the Entognatha, and in particular, Collembola, were closer to Pancrustacea than any base ancestor shared with Insecta. The six legs that Entognatha and insects once had in common are maybe less of a link than a coincidence. Especially as both Diplura and Protura both have retained extra leg-like appendages, so really, only Collembola count...
Even more recent research, such as the 2013 paper by Sasaki et al, suggests a separate lineage for Protura, with a closer linkage between Diplura and Colembola to insects. It's damn tricky. Even the constructed class of Entognatha is questionable, with the three sharing very little in common, least of all, genetics.
It's hard not to anthropomorphise Collembola, especially the Symphypleona, the globular springtails who as their name suggests, are rounded rather than elongated or flattened. They look cute and chubby, often with big, black eye patches and a tendency to turn their heads upwards, as if they were looking back. The freshly hatched have even bigger eyes for their size, with the big heads and smaller bodies of most babies across the world. They just want to be hugged. If only they wouldn't squash..
Collembola can be split into three, or, more controversially, four orders. The Entomobryomorpha, Poduromorpha, Symphypleona and that controversial one, Neelipleona. At the risk of disagreement, and because I really love the Neelidae, I'm going to keep to the four groupings, to give them the status that they obviously deserve....
Entomobryomorpha is a ridiculously long name for a large order of very tiny Collembola. But that's the name they've ended up with so we just have to deal with it.
The Entomobryomorpha describes an initially morphological similarity between different families of Collembola, where their body shape is elongated with a clear separation between the thorax and the first abdominal segment. Many genera have a body covered with scales, perhaps serving as a predator deterrent and very often have many long and short setae protruding from their segments. They have some of the longest antennae of all the springtails, with one species boasting antennae three times its body length.
The Poduromorpha are the jelly fruits of the Collembola. They have short stubby legs and a usually plump, often flattened body.
The character in the title picture, a Podura aquatica, lends its name to the entire group. It's an unusual animal, being pretty much the only genus and species in its own family. They also have a strange, fully aquatic life cycle, laying eggs that drop to the bottom of the water. When hatched, the young have a hydrophobic cuticle, so are immediately thrust upward and out onto the water surface, where they spend the rest of their lives.
The families in Poduromorpha also exhibit some amazing and bizarre differences in shape, with the naturally water-repelling granular cuticle warping and changing between genera, sometimes with mounds and tubercles rising regularly over the body like a 1960s swimming cap. Others fatly expand, leaving a tiny head half-buried beneath a waddling, mounded body, or flatten, spreading out to an undulating frill, legs half hidden beneath the overhang.
Many Onychiuridae and other furca-less or furca-reduced genera of the Poduromorpha have evolved non-springing chemical defences instead, exuding hemolymph to repel attackers. Other springtails, both with and without furcas, have anal spines which can have a defensive and anchoring effect. Stop snickering at the back.
Neonaphorura duboscqi, a member of the subfamily Tullbergiinae has a grand total of six anal spines, the most of any of the Collembola.
The white, sightless springtail above is Anurida granaria, a cosmopolitan species with a huge Northern hemisphere range. Unfortunately, it has also been transplanted into Australia and New Zealand by human activity, where it thrives. But because of this, its ability to bioluminesce was first noticed in 1982 by a New Zealander, Graham East, living near Christchurch, when he turned some wood over in his back garden. It's probable that the bioluminescence is some sort of defensive strategy, as there is just a brief flicker of green for a few seconds when disturbed. This isn't something usual for springtails, and especially unexpected in such a well known species.
Without doubt the cutest order of all the springtails, the Symphypleona are globular, with a distinctive, rounded body shape and usually long antennae. Often multi-coloured, and nearly always with at least some ocelli, one of their defining characteristics is having some fused thoracic and abdominal segments, as opposed to the separate and distinct segments of the Poduromorpha and Entomobryomorpha. They don't seem to be able to get any larger than 3.5mm, so all the people who really want a genetically modified giant Symphypleona as a pet to walk in the park must sadly let that one go. It's a terrible shame.
Adephoderia regina, above, is from an unusual family of springtails, the Spinothecidae. They all have a bizarre neck organ, probably used in oxygen exchange. The genus Adelphoderia has the largest and most impressive organ, obvious even under a hand lens, while the other Spinothecidae have smaller, thin tube-like organs, often hidden by the angle of the head.
The Neelipleona contain the smallest species out of all the springtails as well as containing only six genera. They are all cryptic, lacking pigment or eyes.
All the Neelidae have an unusual head down against the wind manner, with truncated antennae though long enough still to have contact with the soil surface. Hopkin famously once referred to Megalothorax minimus as 'a tiny old man hunched in a baggy coat'. It's an apt a description as any.
Neelides species are the only members of the Neelipleona that have colour- variations on a bluish-grey pigment. The undescribed Australian Neelides species in the first two photos below have the brightest blue I've seen in the genus. They are always under 1mm big, though sharing a similar body shape to Neelus.
The Megalothorax genus and the few other closely related genera are the smallest in the Neelidae, no more than 0.6mm at their largest but usually much smaller. Like Neelus, they have no pigment, instead having the white and orange associated with cave and deep leaf litter/soil collembolans. On older specimens, like the Megalothorax minimus below, dorsal patterning can be seen.
Eggs of Sminthurides aquaticus on pondweed
Eggs of Sminthurides aquaticus on pondweed
They're pretty much a rainbow of flavours.