Sampling Earthworms

A standardised method for sampling earthworms 

 What you will need:

  • OS map or GPS to record the exact location of your site.
  • A spade to dig the soil pits.
  • A plastic sheet or bin liner for sorting through the soil.
  • Plastic gloves.
  • Five bottles of 0.75 litre of mustard solution. To make the mustard solution, add 25 ml volume of mustard powder to 0.75 litre of tap water and shake well.
  • Plastic tubes with screw tops containing 80% ethanol for preserving the earthworms.
  • Five small plastic bags for taking soil samples, for measuring soil pH.

 

The method consists of four steps, and includes digging soil pits and searching microhabitats to collect earthworms. It is recommended that at least two people do the sampling together. One site should take two people about two hours to complete.

 

1. Choosing the sampling site
Find an area that looks representative of the habitat type you wish to sample. If possible, the sampling site should be an area of at least 100m radius. Try and avoid locating the sampling site close to the edge of the habitat, as this may not be representative. The soil pits should be positioned roughly as shown in the diagram (to be added soon). In extreme cases, the soil pits can be positioned in a line to fit a narrower patch of habitat. Using a GPS or OS map to record the geographical position of the sampling site.

 2. The five soil pits

  1. Each soil pit is 25cm x 25cm.
  2. Dig the pit to a depth of 10cm as quickly as possible, and place the soil on a plastic sheet.
  3. Pour 0.75 litre mustard solution into the pit you have just dug.
  4. Keep checking the pit for ten minutes to see if earthworms emerge.
  5. Sort through the soil removed from the pit to search for earthworms.
  6. Check among the roots because earthworms can hide there.
  7. The soil from one pit should take two people no more than 10 minutes to search.
  8. Preserve any earthworms in alcohol.
  9. Label the samples with the pit number and whether it was from the top 10 cm of soil or extracted using the mustard solution.
  10. Collect about 50 g of the topsoil from each pit into a small plastic bag so the pH can be measured.

 3. Searching microhabitats for earthworms
After you have finished the five pits, search for microhabitats within the perimeter of sampling site. Two people search microhabitats for 10 minutes each (i.e. 20 minutes in total). Microhabitats include: inside grass tussocks, under dung, under dead wood, under dead bark or inside very rotten wood, inside piles of leaf litter. Try and sample as many microhabitats as the time allows. Collect any earthworms found and label with a description of the microhabitat. Some habitat types, such as grassland, may have very few microhabitats, so you may not need the full 10 minutes.

 4. Earthworm identification
You will need a microscope and a copy of Earthworms by Sims & Gerard (1985). The Earthworm Society of Britain plans to run identification workshops to help you develop your identification skills. Please contact us if you plan to sample earthworms: info@earthwormsoc.org.uk.

 

Health & Safety


You should carry out your own risk assessment before doing fieldwork. We recommend the following precautions:

  • Never do fieldwork on your own.
  • Always ask permission from the owner before entering private land.
  • Always tell a responsible adult where you are going and what time you expect to return.
  • Check the weather forecast before doing fieldwork, and take appropriate clothing.
  • Be aware of local hazards such as dangerous wildlife or hazardous terrain.
  • Always take a mobile phone and a map of the area.
  • Know who to contact in the event of an emergency.