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Sminthurus viridis, the Lucerne Flea. Source: gnu-www.aquaportall.com

THE WORLD BENEATH OUR FEET: Part 7 - Springtails

BARRY MUIR

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 fl ick 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:

• 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

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 benefi cial 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 fl oor 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.

They tend to occur in groups or clusters, driven by the attractive power of pheromones (‘hormone fragrances’) excreted by the adults. This gives more chance to every juvenile or adult individual to fi nd suitable, better protected places, where drying out can be avoided and reproduction and survival rates are best.

In Australia there is one species, Sminthurus viridis, the Lucerne Flea, which has been shown to cause severe damage to agricultural crops and is considered a pest. Like nearly all our pests, it was probably introduced from Europe.

The more common, local, species carry spores of mycorrhizal fungi and mycorrhiza ‘helper bacteria’ on their bodies.

Soil springtails play a positive role in the establishment of plant-fungal cooperation and thus are benefi cial to agriculture. They also contribute to controlling plant fungal diseases through their active consumption of mycelia and spores of damping-off and pathogenic fungi. For this reason they are especially welcome in plant propagation areas and on potted plants. Even more so than earthworms, Springtails are very sensitive to herbicides and thus are threatened in notillage agriculture, which makes a more intense use of herbicides than conventional agriculture. In fact, their extreme sensitivity to pollution makes them useful indicators of soil quality.

Springtails also play an important role in distributing the spores of soil bacteria, especially Streptomyces, a bacterium involved in maintaining soil health and from which many antibiotics are derived. The bacteria produce a chemical called geosmin which attracts the springtails and encourages them to eat the spores and move them around. Geosmin, incidentally, is the chemical that causes that wonderful smell of wet earth when it starts to rain.

If you want to catch some collembolans (and other tiny beasties) to have a look at them, I have found the following technique eff ective: put a small lump of blue cheese (any type) in a clean jam jar with a wet tissue in the bottom (to keep it moist) and bury it in the ground up to the top of the neck; then place a handful of leaf litter over the opening to darken the jar. In a day or so, fl ip the leaves off and slam the lid on the jar ... got ‘em!

These little pink guys are very common living amongst rotting mushrooms in Flecker Garden.

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