Soil Biodiversity UK

Resources, links, species lists and species information about life in the soil

Finding and Capturing Soil Organisms

This page will explain how to capture and observe soil organisms.  Soil organisms are hugely numerous in the top few centimetres of soil and litter, but the world they inhabit is very complex and provides plenty of places for them to hide.

Larger organisms can be found simply by sorting thorugh soil and searching for the organsms by eye.  Earthworms are often surveyed by digging 5 small pits, levering out a square block of soil a standard spade's width and 10 cm deep, and sorting through the soil by hand on a tray, placing all the earthworms found in a pot (which often contains methylated sprits for preservation of the specimens for later identification).  This technique may also yield other larger soil animals, such as larger fly and beetle larvae, or geophilomorph centipedes.

It's also worth searching under logs, stones, bark, in rotting logs, among moss and in other soil-like habitats.  Larger animals here can be simply captured by hand.

For smaller animals, which may be damaged or lost if you attempt to grab them with fingers, a pooter is a useful and easily made device for sucking specimens into a pot.  Find a small air-tight pot, drill two holes in the lid, and insert two lengths of tubing  - one about 15cm long and one about 30 cm long. Fishtank air line tubing is good for this and it's helpful if you can find two different colours of tubing to help you remember which tube to suck.  Place a piece of fine-weave fabric over the end of longer tube poking through the pot lid, and secure it in place by looping a rubber band around it several times.  Close the pot, and your pooter is ready.  Place the shorter end of the tube near the specimen to be capture, and place the end of the other (fabric-ended) tube in your mouth. Give a short suck, mainly using your mouth rather than lungs, and the specimen will be sucked up the short tube and land in the pot.  If you have several pots of the type you've made the pooter out of, then you can replace the pooter-lid with an unmodified lid, to store the specimens, and place a new pot base under the pooter lid for the next capture.

For some microhabitats, a pooter can be used to capture speciments of mites, springtails, diplura etc. spotted by eye.  Turning over rocks, logs etc can provide many specimens, but leaving a plank of smooth wood on a surface overnight, then searching its underside in the morning can also yield good numbers of soil creatures.  Otherwise, it's helpful to try to seperate the creatures from the soil/litter.  One way to do this is sieving.  Use a kitchen sieve with quite large holes - 2mm spacing is good, and place a handful of soil or litter in the sieve, then gently bounce it up and down over a white tray.  After a few bounces, examine what's fallen out.  You should be able to see many small to tiny moving things ont he tray surface, which can be collected with a pooter. 

A more complete picture of smaller soil animals can be gained by methods that make use of the animals' own movements.  Mesofauna arthropods can be extracted by putting  a block of soil, litter, moss etc in an ordinary plastic kitchen funnel lined with a piece of 2 mm metal gauze (availble from car repair shops).  Suspend the funnel so that the narrow end reaches well into a collection pot (50ml centrifuge tubes available from school suppliers are good for this).  The collection pot can either contain water (for collecting live specimens) or industrial methylated spirits (for preserved specimens).  Placing the collection pot in a tall (pint) glass and resting the wide part of the funnel on the glass rim is a good way to arrange this.   Finally set up a posable bedside lamp with a 40W incandescent (not energy saving!) bulb, so that the bulb is about 5cm from the surface of the soil, and turn on the lamp.   Depending on how wet the material is, after 2-5 days the sample will be dried out, and as it dries the small arthropods will crawl out of the substrate, through the mesh and fall down the funnel into the colleciton pot.

Nematodes can be effectively extracted from soil by letting them wriggle out of half-submerged soil, and collecting them at the bottom of a funnel.  Leave some tap water to stand for a while to allow chlorine to dissipate.  Put some water into a small collecting tube, and attach the tube to the base of a small funnel using a piece of tubing or tape to make a watertight seal. Add more water so that it partially fills the funnel.  You now need to suspend the soil half in the water.  A simple approach is to make a sort of "soil teabag": put a teaspoon of soil onto a square of fine cloth - squares cut from a pair of tights work well - draw up the edges and seal the bag with a rubber band before half-submerging in the water in the funnel.  A more professional approach involves forming a piece of metal mesh into a flat platform so that it will lie horizontally just beneath the surface of the water in the funnel, and lining it with one ply of paper handkerchief, place the soil or litter on the paper and lowering it into the water in the funnel, so that the soil is damp, but not entirely submerged.  In both approaches the nematodes will wriggle out of the soil, through the barrier, and fall through the water to collect at the bottom of the tube - this usually takes no more than 2 days and many can be collected overnight.  You can then remove the funnel carefully, letting the water drain out without washing away your sample, and collect and view your nematodes from the bottom of the tube, either using a pipette, or pouring it out onto a microscope slide with a deep chamber.

Protozoa, nematodes, rotifers, tardigrades and other soil water animals can be observed by making a slurry of soil with water in a small dish and putting some of this slurry under a microscope.  This is particuarly effective with moss samples, which often yield all these groups.

Scratchpads developed and conceived by (alphabetical): Ed Baker, Katherine Bouton Alice Heaton Dimitris Koureas, Laurence Livermore, Dave Roberts, Simon Rycroft, Ben Scott, Vince Smith