An introductionto earthworms

Summer 2016

ImportanceEarthworms can be used as anindicator of soil quality becauseworms are uncommon in soils thatare compacted, waterlogged, haveextremes in soil pH or are verysandy.

Many arable management practiceshave an impact on the number ofearthworms present in soil, particularlytillage intensity, food supply (soilcover, residue management) andagrochemical applications.

Earthworms provide free labour(nature’s ploughs) and fertiliser bybreaking down organic matter,allowing bacteria and fungi to releasethe nutrients into the soil. Increasingearthworm populations in arablefields can be beneficial to cropproduction.

Epigeic earthwormsEpigeic earthworms are litterfeeders found on and in the soilsurface (< 3 cm). They are thesmallest earthworms and haveshort life cycles.

Endogeic earthwormsEndogeic earthworms are found inthe topsoil (>2 cm to 40 cm deep).They are bigger than epigeicearthworms, typically the size of amatchstick.

They make a network oftemporary burrows throughout thesoil profile. They mix the soil,redistributing soil bacteria andproducing faeces (casts) rich innutrients (N, P, K, S).

Endogeic earthworms are themost common earthworm groupfound in arable fields.

Anecic earthwormsAnecic earthworms make deepvertical tunnels (up to 2 metres)and inhabit their tunnel throughouttheir lives. They are the largestearthworms – often the size of apencil – and can live for up to fiveyears.

They feed at night, foraging the soilsurface around their burrow forlitter. Anecic earthworms improvesoil porosity and aeration, as wellas aiding water infiltration bybuilding permanent vertical tunnelsthrough the soil.

They are often absent in fieldsmanaged with intensive cultivationsand no surface litter (for example,root cropping, ploughed soils).

Types of earthworm

Not to scale

Assessing earthworm populations

© Agriculture and Horticulture Development Board 2016. All rights reserved.

While the Agriculture and Horticulture Development Board seeks to ensure that the information contained within this document isaccurate at the time of printing, no warranty is given in respect thereof and, to the maximum extent permitted by law, the Agricultureand Horticulture Development Board accepts no liability for loss, damage or injury howsoever caused (including that caused bynegligence) or suffered directly or indirectly in relation to information and opinions contained in or omitted from this document.

Reference herein to trade names and proprietary products without stating that they are protected does not imply that they may beregarded as unprotected and thus free for general use. No endorsement of named products is intended, nor is any criticism implied ofother alternative but unnamed products.

AHDB Cereals & Oilseeds is a part of the Agriculture and Horticulture Development Board (AHDB).

Further informationJacqueline Stroud, Rothamsted Researchjacqueline.stroud@rothamsted.ac.uk

Amanda Bennett, AHDBamanda.bennett@ahdb.org.uk

cereals.ahdb.org.uk

Images and videos of earthworms, midden building and sampling techniques are available on Instagram#wormhunters2015

When to assess earthworm populationsSpring and autumn are the best times to do earthworm assessments. Timing the sampling after warm, wetconditions often provides the best earthworm estimates.

How to assess earthworm populationsHand sortingOne way to assess earthwormpopulations is to dig a 20 cm x 20 cm x 20 cm hole and hand sortthrough the soil.

As earthworm populations arepatchy, 20 measurements per fieldare recommended.

To estimate the number ofearthworms per m2, multiply thenumber counted in eachmeasurement by 25.

Most conventionally managedarable fields will have around 150 earthworms (matchstick size)per m2.

Mustard extractionThe mustard method can be usedto get a snapshot of earthwormpopulations without damagingcrops. Mustard is irritating toearthworms, so burrowingearthworms will come to thesurface within about 10 minutes.

Pour a mustard solution (1.5 litresof water to 2 tablespoons ofmustard powder) over a 50 cm x50 cm patch of soil and count thenumber of worms that emerge.

Midden counting (anecic earthworms)A fast way of assessing anecicearthworm populations is to countthe numbers of middens on thesoil surface (per m2 area).

Field edges that receive tree litteroften have higher anecicearthworm populations than in thecentre of the field.

Ploughed soil

Minimum tilled soil

Zero tilled soil

0–3

3–15

>15–60

Typicalnumber ofmiddens perm2 (in spring)

20 cm x 20 cm is a typical toolwidth and depth

Middens are the distinctivepiles of organic residues(twigs, leaves, straw, stones)gathered by each anecicearthworm from its nightlyforaging activities

Moving the midden will revealthe entrance to the earthworm'spermanent tunnel (up to 1 cmin diameter)