Lumbricus terrestris

Preferred Scientific Name

• Lumbricus terrestris L.

International Common Names

• English: lob worm; nightcrawler

Local Common Names

• UK: dew worm
• USA: dew worm

• Domain: Eukaryota
•     Kingdom: Metazoa
•         Phylum: Annelida
•             Class: Oligochaeta
•                 Order: Haplotaxida
•                     Family: Lumbricidae
•                         Genus: Lumbricus
•                             Species: Lumbricus terrestris

LumbricusterrestrisLinnaeus (1758) was the first earthworm given a name in the Linnaean system, but there was considerable debate about the identity of the worm, the validity of the name and other aspects of nomenclature because the description was extremely brief and no type specimen was deposited by Linnaeus. The morphologically identical worm EnterionherculeumSavigny (1826) was proposed by some to be the first validly established member of the genus Lumbricus, and the name L. herculeus was in favour with some taxonomists for quite some time (Tetry, 1937; Bouche, 1972). Several other names, now believed to be junior objective synonyms of L. terrestris, were also proposed. Designation of a neotype by Sims (1973) fixed the identity of L. terrestris. Sims (1973) followed the long tradition, at least since Michaelsen (1900), of regarding L. herculeus as a junior synonym of L. terrestris. This was in keeping with the morphological species concept in general use. James et al. (2010) discovered that there are two genetically distinct lineages within nominal L. terrestris, and that these corresponded to L. terrestris and L. herculeus, with the latter as a cryptic species, indistinguishable except by size differences. James et al. (2010) removed L. herculeus from the synonymy of L. terrestris and provided a simple molecular marker, the cytochrome oxidase subunit I DNA barcode (Hebert et al., 2003), which is both necessary and sufficient to identify the two species. DNA barcoding is quite effective on earthworms (Richard et al., 2009). The Sims (1973) neotype was determined to be lost, and has been replaced by a subsequent neotype designated in James et al. (2010). This current neotype has the advantage of being in preservative that does not destroy DNA, and the neotype has been DNA-barcoded.

The restriction of L. terrestris to a lineage first found in the Uppsala Botanical Garden in Sweden, but it also being found widely distributed in Europe and North America, means that much past work on L. terrestris could be unreliable. It is possible that L. herculeus was actually involved for many reported accounts of L. terrestris, or that it was a mix of both species.

External Features

Length 110-200 mm, diameter 7-10 mm, segment number 120-170, mostly 135-150. Body cylindrical in cross section except for broad, flattened posterior. Head end dark brown to reddish brown dorsally, dorsal pigmentation fading towards posterior. Prostomium tanylobous (bearing two small furrows on the dorsal side the first segment, each furrow reaching the first intersegmental boundary), dorsal pores from furrow 7/8 or 8/9; spermathecal pores lateral in furrows 9/10/11 between setae C and D level. Male pores on prominent pads in 15, clitellum 32-37, tubercular ridge 32 or 33- 36. Setae are closely paired, the ventral setae (A) more widely spaced than the ventral couple (A and B), the distance between B and C slightly less than the AA distance, and the CD distance slightly less than AB. Small papillae surround setae A and B on segments 25 and 26 (variable), and in the segments of the clitellum.

Internal Features

Septa present from 4/5; 6/7-9/10 strongly muscularized. Gizzard in 17-19, typhlosole begins in 21. Last pair of hearts in 11. Seminal vesicles in 9, 11 and 12; spermathecae in 9 and 10.

A detailed description of the adult stage can be found in Sims (1973).

Adults and juveniles are not reliably identifiable by any means other than molecular data, for which DNA barcode region is recommended. Cocoons (egg capsules) may be larger than those of most other earthworms in the same location, except where other large-bodied worms such as Aporrectodea longa occur. Therefore, cocoons cannot be reliably identified without molecular tools.

Much speculation has been made about earthworm invasion history in general, but they were probably introduced historically via the horticulture trade, the practice of using earth as ballast in ships between the sixteenth and nineteenth centuries, and the introduction of plants to newly colonized regions. L.terrestris was first described from a population in Uppsala, Sweden in 1758 but it is likely that its introduction and spread to Europe occurred much earlier, before merchants and colonists took much recognition of the species. Due to this lack of interest and so a lack of reported information regarding the species movements, it is unlikely to have originated from Uppsala. It probably arrived in North America at or before this time, but further spread took place much later.

It was not until the nineteenth century that naturalists, including earthworm specialists, began to take note of the earthworms present in various areas. In this regard it is important to recall that until Savigny (1826), the scientific community regarded all earthworms as being of one species, L. terrestris. The pace of species discovery did not accelerate much until the late nineteenth century, by which time it became possible to make intelligent statements about earthworm natural distributions. Only then could a species be said to occur inside or outside its natural range (James 2004).

Michaelsen (1900) indicated that many species were “widely transported”, and the same species, and more, are recognized today as peregrine or invasive species. A good compilation of these is in Blakemore (2006). It was also noted that several earthworm species were possibly displacing indigenous fauna (Michaelsen, 1900; Eisen, 1900; Beddard, 1912). Over the ensuing century there has been a steady accumulation of evidence of earthworm introductions worldwide (Smith, 1928; Gates, 1972, 1982; Ljungstrom, 1972; Stebbings, 1962).

Smith (1928) noticed that L. terrestris invaded an urbanized area of central Illinois, USA, apparently displacing Diplocardia communis in the process.  Pop and Pop (2006) found L. terrestris in new locations in Romania in recent years, indicating on-going invasion of places with indigenous Romanian earthworms. Gates (1972) recounts anecdotal evidence of early twentieth century arrivals in parts of Ohio and Illinois, Washington, and North Carolina. In contrast, some kind of earthworm, possibly L. terrestris, was present in areas of Michigan, Utah, and Idaho by the mid to late nineteenth century.

Gates (1972, 1982) monitored oligochaetes intercepted with imported plants and soils quarantined by the US Department of Agriculture over a 32-year period (1950-1982), and found that earthworms from all over the world were continually being imported into the US. On a more local scale, back-country fishing and off-road recreation (pack animals and motorized vehicles) are significant vectors of transport into remote areas (Hale et al., 2005; Holdsworth, 2007).

Natural Dispersal (Non-Biotic)

Individuals move on the soil surface or within the soil as a result of burrowing (Ligthart et al., 1997). The highest rate of dispersal is achieved during rainfall when the worms leave their burrows and crawl apparently aimlessly on the surface (Mather and Christensen, 1988). Eventually they may find cover and form new burrows, or they may die from exposure to too much sunlight and drying out, or to predators. This is essentially a process of diffusion, so worms are equally likely to travel into areas of established populations or areas free of other individuals of their species. However, because they are obligatory biparental, a single individual cannot establish a new population unless that individual has received sperm in copulation prior to dispersal. It is possible that some water-borne dispersal takes place, but only if the water that the worm has fallen into is not fast flowing and they are able to climb out. All natural dispersal is local and not long distance, averaging less than 10 m per year (Ligthart et al., 1997; Tiunov et al., 2006).

Accidental Introduction

The most common means of transport is accidental inclusion in soils, plant pots, mulches or other materials moved by humans through the agricultural and horticultural trades. Discarding bait also spreads L. terrestris. Back-country fishing and off-road recreation (pack animals and motorized vehicles) are significant vectors of transport into remote areas (Hale et al., 2005; Holdsworth, 2007). Accidental introduction can be local, national or international, as indicated by the fact that the species has crossed many international boundaries and inter-continental boundaries.

Intentional Introduction

These worms may be deliberately introduced as part of soil bioremediation efforts and also to establish new populations for exploitation as fishing bait. Such transport can be local, national or international but introduction is not always successful (Butt et al., 1999).

Impact on Habitats

During the last 100 years, dramatic changes in forest soil profiles caused by exotic European lumbricid earthworms have been reported in Australia and North America (Nielsen and Hole, 1964; Abbott, 1985; Alban and Berry, 1994; Scheu and Parkinson, 1994). Forest floor habitats can be extensively altered by the combined action of L. terrestris and other invasive earthworms (Hale et al., 2005a, b; Alban and Berry, 1994; Bohlen et al., 2004; Suárez et al., 2006). In Minnesota hardwood forests, the effect of any one species is less than the combined effect of three species, including L. rubellus, L. terrestris and one other (Hale et al., 2008). Litter layers are reduced rapidly to humified organic matter and mixed with mineral soil. The native state in areas without natural earthworm populations is to develop thick leaf mats on the forest floor, in which various other soil invertebrates live.

Changes in nutrient dynamics and forest floor plant communities could have long-term effects on forest productivity (Hale et al., 2008). It is speculative to estimate these without further study.

Impact on Biodiversity

The change in the structure, microbial community content, and chemistry of the forest floor is profound (Eisenhauer et al., 2007) and is expected to affect soil invertebrates. Plant communities are also affected (Holdsworth, 2007a, b) with reduced forest floor herb layer diversity and the promotion of some invasive plants.

• Proved invasive outside its native range
• Highly adaptable to different environments
• Is a habitat generalist
• Tolerant of shade
• Capable of securing and ingesting a wide range of food
• Highly mobile locally
• Benefits from human association (i.e. it is a human commensal)
• Long lived

• Altered trophic level
• Damaged ecosystem services
• Ecosystem change/ habitat alteration
• Increases vulnerability to invasions
• Modification of successional patterns
• Negatively impacts forestry
• Reduced amenity values
• Reduced native biodiversity
• Threat to/ loss of endangered species
• Threat to/ loss of native species

• Competition - monopolizing resources
• Competition (unspecified)
• Interaction with other invasive species
• Rooting

• Highly likely to be transported internationally accidentally
• Highly likely to be transported internationally deliberately
• Difficult/costly to control

Economic Value

There is a substantial fishing bait market in North America. Most of the supply is gathered manually from golf courses at night (Tomlin, 1983). 

Environmental Services

Earthworms are ecosystem engineers with diverse physical and chemical effects on soils (Lee, 1985). Taking a positive view of the environmental impact of L. terrestris and other invasive earthworms, it can be said that they perform a number of environmental services, including: modifying the physical soil environment, transforming organic matter and modifying soil chemistry. Earthworms often occupy a key role in nutrient cycling and in the movement of air and water within soils.

However, where an ecosystem has developed in the absence of earthworms, existing communities and ecological relationships can be disrupted by the arrival of L. terrestris or other species. See Environmental Impacts.