Sminthurus viridis, the Lucerne Flea. Source: gnu-www.aquaportall.com
THE WORLD BENEATH OUR FEET: Part 7 - Springtails You have probably never noticed them, but there is a group of critters of which there may be up to 100,000 in a square metre of soil and thousands more of dozens of species on the foliage and trunks of plants in a wellkept garden. They are the Collembola, or Springtails, distantly related to insects. Like insects, collembolans are hexapods, meaning that they have six walking legs, but they never have wings. They can have from two to 16 eyes, but species living in soil are often blind. Springtails are mostly tiny, feed on almost anything and contribute to the recycling of plant, animal and fungal matter mainly by breaking it up into smaller pieces. Their name derives from the fact that they have a tiny ‘peg’ under tension under their abdomen, which they can flick suddenly, throwing them into the air for up to 30cm. Springtails are famous jumpers - if they were as large as humans, they could easily jump over a 10-storey building! They use this ability to escape predators and to move around quickly. They show huge variation depending on where they live: •
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Those that live on plants are generally 8-10mm in length, pigmented, have long limbs and a full set of primitive ‘eyes’. Those that inhabit upper litter layers and fallen logs are slightly smaller, paler and have less developed limbs and eyes. Species that inhabit lower layers of decomposing organic litter are 1-2mm in length, have patchy
BARRY MUIR
pigmentation, short limbs and fewer eyes. •
Those that inhabit the upper mineral layers and humus of soil are even smaller, well under a millimetre, and have soft, elongated bodies and no pigment or eyes.
They may be tiny, but they have an important role to play just by sheer weight of numbers. They fragment and consume plant debris and pollen, animal remains and bacteria present in soil and leaf litter, aiding recycling and increasing the availability of nutrients for beneficial bacteria and fungi. Carnivorous species control populations of nematode worms and other minute soil pests, while by sheer weight of numbers they provide food for many carnivorous soil creatures like spiders, beetles and ants. Springtails are extremely common on the floor of forest; there can be thousands of them in a handful of fallen leaves. They are commonly associated with fungi, like the pink ones pictured on the next page, but are found in Antarctica on snow and rocks, in tree canopies of tropical forests, and on the highest mountains and down in the deepest caves. I once found an undescribed species over a kilometre into a cave under the Nullarbor Plain. Springtails have also been around for a while, thriving on the planet long before dinosaurs, with a fossil springtail dated at about 410 million years old. Some modern springtails look very similar to this ancient fossil, so they have survived four major global extinctions without changing very much in appearance.
