Earthworm

A mostly soil dwelling animal, of which the Earthworm Society of Britain currently identify 27 named species in the UK. These are typically allocated into three categories:
1. Epigic: Surface dwellers (that are typically a red colour) of litter, composts and decaying wood. Sometimes the earthworm species which reside in compost heaps or organic waste (such as cow pats) are included in a separate group termed the composters.
2. Endogeic: horizontal burrowers, typically greyish or pinkish in colour. They occur deeper within the soil, expelling their casts within the soil, and rarely, or do not commonly, come to the surface.
3. Anecic: vertical burrowers, typically darker brown in colour, which are deep burrowers that expel their casts on the surface, typically at night. Some of the species within this category cause the most concern to grounds managers and impact on playing quality, especially on fine turf surfaces.

A typical lifecycle for an earthworm is as follows: They grow from egg capsules, which are laid mainly during spring and autumn. They take from one to six months to emerge depending upon the temperature and adequate soil moisture.

During dry, hot and cold weather earthworms will go into a state of inactivity, coiling themselves up, at depth, to conserve body moisture. This is why there is a lack of surface casting at certain times of the year. Most earthworm activity appears to be in the temperature range 10 to 15C, which is consistent with high activity in May and September in most of the British Isles.

The young (also called juvenile) earthworms develop into adults over a few years and the smaller species may live for up to 12 years, with some larger species having lived for 30 years in 'captivity'.

Earthworms feed mostly on organic matter from either live plant material, for example roots, or decomposing remains, for example grass clippings. In addition, they will also feed on algae, fungi and bacteria. Earthworms are members of the Annelida phylum and are commonly just referred to as worms.

Earthworms vary considerably in size, but maybe 40mm to 150mm might be typical for many found within many turfgrass situations. They are beneficial to the soil ecology and its health, they improve soil aeration and provide a gradual slow release of nutrients from organic matter broken down in the soil.

References:
Sherlock, E. (2012) ‘Key to the earthworms of the UK and Ireland’, FSC and Natural History Museum.
Sims, R.W. and Gerard, B.M. (1999) ‘Earthworms’, Synopses of the British Fauna (New Series), No.31 (Revised), FSC
Wallwork, J.A. (1983) ‘Earthworm Biology’, Studies in Biology no. 161, Edward Arnold Ltd

Other benefits of earthworms include:
1. The incorporation of grass clippings rapidly into the soil profile.
2. The mixing of soil components which reduces layering in the soil profile.
3. Encouraging deeper rooting of grasses.
4. Improve soil drainage.
5. Producing a better structured and aggregated soil.
6. Promote humus formation.
7. Enrich soil nutrient levels.
8. Reduce the need for mechanical aeration and scarification.
9. They can save maintenance time and costs. There are three main earthworm species which produce casts on the surface of a turf area, and these have a detrimental effect on the overall quality of that surface where numbers are excessive.

There are significant limitations and disadvantages to a heavy earthworm population, especially the surface casts from a few of the species, including:
1. Casts are nutrient rich, with a relatively high (i.e. more neutral) pH, producing an ideal seed bed for weeds and weed seeds.
2. Reduce surface infiltration when smeared.
3. Smother desirable grasses.
4. Produce a softer surface, with less traction for users.
5. Produce minor surface unevenness.
6. Reduce the effectiveness of sand-slit drainage systems, due to capping over of the slits.
7. Increase disease susceptibility.
8. Reduce the playing quality experience.

The commonest earthworms which are prone to surface casting, of which there are just three, are:
• Lumbricus terrestris.
• Aporrectodea longa.
• Aporrectodea caliginosa.

(Mann, R.L., ‘A review of the main turfgrass pests in Europe and their best management practices at present’, Journal of Turfgrass and Sports Surface Science Vol.80 (2004), pp2-18)

[Note.: “Aporrectodea caliginosa was previously known to exist as a distinctly different morph: nocturna. This morph is an anecic earthworm, whereas A. caliginosa is typically an endogeic earthworm. Research that is due to be published in 2018 has demonstrated through both molecular and morphological work that the nocturna morph is in fact a distinct species: Aporrectodea nocturna.” https://www.earthwormsoc.org.uk/species-uk, accessed 4th October 2024]

There are other species which might occasionally contribute to localised surface casting, although under-reporting and limited detailed and routine studies make these species lists incomplete:
• Aporrectodea rosea in compacted finer soils.
• Allolobophora chlorotica.
• Lumbricus rubellus.
• Lumbricus festivus.
• Allolobophoridella eiseni (formerly Lumbricus eiseni);
• Dendrobaena octaedra.

References:
Kirby, E.C. & Baker, S.W. ‘Earthworm populations, casting and control in sports turf: A review’, Journal of the Sports Turf Research Institute Vol.71 (1995), pp84-98.
Dawson, R.B. (1959) ‘Practical Lawn Craft and Management of Sports Turf’, pp184-185.
Natural England Commissioned Report NECR145 (2014) ‘Earthworms in England: distribution, abundance and habitats’, http://publications.naturalengland.org.uk/publication/5174957155811328
From a turf management perspective, the ideal situation would be to encourage all earthworms to produce casts within the soil profile and not on the surface of the grass.

Earthworms might be able to be controlled in a number of ways.

• Chemical control, but there may not be any approved chemicals for use.
• Cultural and physical control can help with earthworm reduction rather than immediate control.

Examples of activities to help reduce earthworm activity and potential for encroachment into a turf surface can include:
1. Drag brush or switch to disperse casts.
2. Scarify and/or hollow-tine to remove thatch.
3. Box off clippings to remove their food source.
4. Avoid neutral to alkaline reacting fertilisers.
5. Avoid neutral to alkaline top-dressings.
6. Avoid the application of lime.
7. Use acidifying fertilisers (but use carefully and only if appropriate to the desired grass species present).
8. Consider reducing the use of organic fertilisers (although this may be a conflict with the aims of a sustainable turfgrass surface); A more appropriate approach may be to ensure organic fertilisers are not applied either too early or too late in the growing season, as this is when earthworm surface activity can be high.
9. Use top-dressings which are slightly acidic.
10. Test the pH of irrigation water; counter measures to increase acidity may need to be taken if it is alkaline.