Survival and growth of Lumbricus terrestris (Lumbricidae) fed on dung from cattle given sustained-release boluses of ivermectin or fenbendazole

The effects of faecally excreted ivermectin and fenbendazole, and their metabolites, on the survival and growth of the common pastureland earthworm Lumbricus terrestris, have been studied in the laboratory. Hatchlings were fed dung voided by untreated cattle or cattle given sustained-release boluses of the antiparasitic agents ivermectin or fenbendazole. Hatchling survival and growth rates were followed until maturity. The survival of worms fed untreated dung was 100% whereas survival in ivermectin and fenbendazole groups was 97 and 91%, respectively. The first worms became mature 16 weeks after hatching, irrespective of dung type, and all worms were mature 24 weeks after hatching. The growth rate of the worms fed dung from cattle given ivermectin boluses was 2.6 mg higher day^–1 than that recoded for the control group, whereas the growth rate of worms fed on dung from cattle given fenbendazole boluses did not differ significantly from the control group. It may be concluded that ivermectin, fenbendazole and their metabolites had no adverse effects on the survival and growth of L. terrestris when exposed through dung under laboratory conditions.     

Assessing daily egestion rates in earthworms: using fungal spores as a natural soil marker to estimate gut transit time

Earthworms have an important role in ‘bioturbation’—the mixing of soil due to biological processes. Quantification of earthworm bioturbation relies on estimating earthworm egestion rates which in turn depend on two parameters: the gut content of the worms and the gut transit time (GTT). Gut content can be determined relatively easily, but determining GTT is problematic. The present study aimed at estimating daily soil egestion rates of Aporrectodea caliginosa and Lumbricus terrestris, refining the most common approach for estimating GTT by using fungal spores as natural markers in ingested soil. This approach avoids the use of artificial markers that may adversely affect the earthworms. Gut transit time was estimated by tracking the passage of marked soil through the gut by the appearance of the spores in the egested faeces. Gut transit time was estimated to be 9.6?±?0.3 h for A. caliginosa and 11.6?±?0.5 h for L. terrestris. Gut content averaged 465?±?40(± standard error (SE))?mg dw g^?1 dw worm for A. caliginosa and 265?±?80 mg dw g^?1 dw worm for L. terrestris. From these values, daily egestion rates of 1.16 and 0.66 g dw faeces g^?1 dw worm d^?1 were calculated for A. caliginosa and L. terrestris, respectively. Both values compare well to literature values for each species. The presented method for GTT estimation is inexpensive, rapid and easy to evaluate, with spores being a good alternative to existing markers.     

Influence of organic matter on earthworm production and behaviour: a laboratory-based approach with applications for soil restoration

Restored soils are often low in organic matter (OM). As a result, OM is applied to increase soil fertility. Earthworms can assist soil incorporation of OM, but feeding behaviours, and as a result their roles in this process, differ between species. Laboratory experiments examined the effects of OM availability on the growth and behaviour of Aporrectodea longa and Lumbricus terrestris. Hatchling growth was recorded from 1 l vessels containing soil and OM (separated cattle solids), either surface applied (SUR) or mixed into the soil (MIX). Growth of L. terrestris was also recorded where separated cattle solids (SCS) were concentrated in bands at the surface (SUR) or at depths of 0.03 (UPP) or 0.08 m (LOW). In a further experiment, L. terrestris and L. rubellus were kept in mono-species cultures and paired combination, in treatments with selected SCS placements, which allowed assessment of OM position on species interactions. After 28 weeks, both L. terrestris and A. longa exhibited significantly greater growth rates (P < 0.05) in SUR treatments. The behaviour of both species changed with time. L. terrestris were located in areas where OM was concentrated. After 24 weeks, mean masses of 3.1, 2.2 and 1.6 g were recorded for SUR, UPP and LOW treatments, respectively. Where L. rubellus and L. terrestris were co-cultured, the former had significant (P < 0.05) negative effects on the growth of the latter, but only when surface OM was limited. At restored sites, application of OM may be important in the development of sustainable earthworm populations and hence their role in soil amelioration.     

The interactions between soil type and earthworm species determine the properties of earthworm casts

Earthworms are recognized to increase soil porosity, reorganize soil structure, and stimulate soil microflora and nutrient mineralization. The properties of earthworm casts should depend both on earthworm species or ecological group and on soil properties. Interactions between earthworm species and soil types have been suggested, but only poorly demonstrated. In order to better understand those interactions, two hypotheses led our study: (1) Soil type has a greater influence on cast properties than earthworm; (2) Earthworms from different species influence cast properties differently; (3) The intensity and direction of the impact of each earthworm species on cast properties vary with soil properties. Fifteen physical and chemical variables (N–NH₄⁺, N–NO₃⁻, total organic C and N, C/N ratio, CaCO₃, pH, P, K⁺, Mg²⁺, Mn²⁺, Na⁺, CEC, moisture, wettability) were measured in casts of three earthworm species (Lumbricus terrestris, Allolobophora chlorotica and Aporrectodea rosea) produced in three temperate soils. Univariate and multivariate analyses showed that earthworm species and soil types significantly impacted cast properties. pH, N_t, K and Mg contents were interactively altered by both factors. Multivariate analysis showed that a difference of soil type had a major impact on casts properties (62%) compared to the impact of a difference of earthworm species (10%). Cast properties were most impacted by L. terrestris, then by A. chlorotica and last by A. rosea. The response ratio (ratio of the properties of the casts to the properties of the bulk soil) was used to quantify the effect of earthworm species compared to the control soil. It showed a higher response of variables in casts in nutrient-rich soils, especially in casts of L. terrestris. The interactions between earthworm species and soil types on cast properties were discussed with regards to earthworm ecology, properties of the soil, and earthworm modifications of cast microflora.     

Effects of ivermectin in dung pats on earthworm (Megascolecidae) populations and pat degradation in Japanese grassland

The effects of residual ivermectin in dung pats on earthworm activity and dung decomposition in Japanese grassland, where Megascolecidae are the dominant group of dung decomposers, were studied. Artificial cowpats containing 0, 0.1, and 1 mg ivermectin kg⁻¹ dung were prepared and deposited on grassland in October 2003. Pats were collected again for analysis 1, 3, 5, and 7 weeks after deposition. Earthworms were collected from the soil around pats at a depth of 0–10 cm. The Megascolecidae, Pheretima (Amynthas) heteropoda and Pheretima (Amynthas) divergens, together accounted for more than 90 and 99% of earthworm individuals and biomass, respectively. Earthworms aggregated around the pats regardless of the ivermectin treatment. Dung-degradation rate was also unaffected by the ivermectin treatments. Dung decomposition appeared to be due mainly to earthworm activity, as dung beetles were rare at this site. These results suggest that ivermectin may have no adverse effects on Megascolecidae activity and on the degradation of cowpats in pastureland sites where earthworms dominate the dung decomposer community.     

C and N turnover of fermented residues from biogas plants in soil in the presence of three different earthworm species (Lumbricus terrestris,Aporrectodea longa,Aporrectodea caliginosa)

A soil microcosm experiment was performed to assess (1) the C- and N- turnover of residues from biogas plants in soils in the presence of three earthworm species (Lumbricus terrestris, Aporrectodea longa and Aporrectodea caliginosa) and (2) the resulting changes in soil chemical and microbiological properties when using these residues as fertilizer in comparison to conventional slurry. Earthworms were exposed in soils, fertilized with an equivalent amount of 120 kg of NH₄-N ha^?1 from: (1) conventional cattle slurry and (2) a fermented residue derived from cattle slurry, grass (silage) and maize. Additional treatments without slurry and earthworms were used as controls.There was considerable evidence that soils fertilized by fermented slurry comprised fewer amounts of readily available nutrients for microbial C and N turnover. We observed significant stimulation of microbial biomass, basal respiration and nitrification in treatments with conventional slurry, especially in the presence of earthworms. However, the stimulation of microbial activity by manure and earthworms were significantly lower in treatments with fermented slurry. Moreover, the results showed clear interactions between different earthworm species and manures. While the biomass of the anecic species (L. terrestris and A. longa) increased in both slurry treatments, the biomass of A. caliginosa (endogeic) decreased, with a significantly stronger biomass decline in treatments with fermented slurry. The metabolic quotients revealed microbial stress metabolism in fermented slurry treatments, predominantly in treatments with A. caliginosa. We conclude that particularly A. caliginosa and soil microorganisms competed for labile C sources in treatments with fermented slurry. An application of these residues as fertilizer might result in a reduction of microbial activity in agricultural soils and in a decline of endogeic earthworms.     

Does reproductive plasticity in Lumbricus rubellus improve the recovery of populations in frequently inundated river floodplains?

Flooding events often eradicate all of the individuals of the earthworm species Lumbricus rubellus living in river floodplains, although earthworm cocoons usually survive immersion, permitting populations to recover after the flood waters recede. Yet, if the area is flooded again before earthworms hatching from cocoons or migrating from adjacent areas reach reproductive maturity, it is unlikely that their populations will recover. The objective of this study is to determine the importance of the length of the dry period for population recovery in L. rubellus. Earthworms were collected at three floodplain sites along the Rhine River that were frequently, moderately or seldom flooded. Reproductively mature L. rubellus from the frequent flooded site were half the weight and probably younger than those from the other sites. A mechanistic population model was used to estimate the time for earthworm development from hatching to reproductive maturity, and to calculate the probability of population recovery after flooding. The model results show that the probability of extinction increases when the dry period is not long enough for individuals to reach reproductive maturity. When this condition is met population extinction is virtually absent resulting from the high lifetime reproductive output of L. rubellus. Parameterization of the model with site-specific data indicate that population survival on the site with the shortest dry period drastically decreases if worms mature at the weight measured at the other sites. The results therefore strongly suggest that the dry period is critical for population recovery in river floodplains and that earthworm populations have adapted to local (site-specific) conditions.     

Fat but slim: Criteria of seed attractiveness for earthworms

Earthworms were shown to significantly affect seeds and seedlings survival via their ingestion and digestion for nutritive purposes. Such selective feeding of earthworms on plant seeds is likely to favour certain plant species and to affect seed bank composition, plant recruitment and plant community structure. Relationships between earthworms and seeds, particularly seed traits that determine attractiveness of seeds for earthworms, are yet to be determined. In this study, the influence of six seed traits was tested on the ingestion, digestion and germination of seeds by two earthworm species (Lumbricus terrestris, anecic and Satchellius mammalis, epigeic). The seed traits tested were their length, width, weight, shape, oil content and the presence of trichomes on their surface. Each earthworm species was introduced into a microcosm with eleven seed species from a chalk grassland that represented those different traits. Ingested, digested and germinated seeds were counted after voiding the guts of the earthworms. Univariate and multivariate analyses showed that seed length, width, weight and seed oil content could significantly affect the ingestion of seeds for both earthworm species. Seed width and seed oil content were the two traits that influenced the digestion of seeds the most, but only for L. terrestris. We also found that seed ingestion was earthworm species-specific but we found no correlation between earthworm traits and number of ingested or digested seeds. Few seeds germinated from L. terrestris casts and no seeds germinated from S. mammalis casts. Implications in terms of plant evolution strategies are further discussed.     

Depth of cocoon deposition by three earthworm species in mesocosms

Earthworms were maintained in two types of soil-filled mesocosm. Type 1, designed for use in soil-inoculation studies, was only 0.15 m deep. Sampling revealed the position at which cocoons were deposited by earthworms in mono-species culture. Whilst adequate for shallow-working worms, larger species may have experienced restricted burrow formation and associated cocoon deposition. Therefore, Type 2 mesocosms (1.0 m deep) were also used. Here, earthworms were found to burrow throughout the soil columns, but cocoons were mainly deposited within 0.25 m of the soil surface (95% overall). The deepest cocoon deposition was at 0.4 m by Lumbricus terrestris, although 45% of the cocoons for this species were located in the upper 0.05 m of the soil, compared with 70% and 71% for Aporrectodea longa and Octolasion cyaneum, respectively. Comparisons between mesocosms showed that their depth affected cocoon distribution in the soil and that differences were also present compared with field-collected results. Reasons for this are discussed, as are implications for soil inoculation with earthworms. If cocoons are viewed as a potential inoculum for soil restoration work, their harvesting and spreading in soil may assist successful colonisation.     

Impacts of earthworms and arbuscular mycorrhizal fungi (Glomus intraradices) on plant performance are not interrelated

Earthworms and arbuscular mycorrhizal fungi (AMF) might interactively impact plant productivity; however, previous studies reported inconsistent results. We set up a three-factorial greenhouse experiment to study the effects of earthworms (Aporrectodea caliginosa Savigny and Lumbricus terrestris L.) and AMF (Glomus intraradices N.C. Schenck & G.S. Sm.) on the performance (productivity and shoot nutrient content) of plant species (Lolium perenne L., Trifolium pratense L. and Plantago lanceolata L.) belonging to the three functional groups grasses, legumes and herbs, respectively. Further, we investigated earthworm performance and plant root mycorrhization as affected by the treatments. Our results accentuate the importance of root derived resources for earthworm performance since earthworm weight (A. caliginosa and L. terrestris) and survival (L. terrestris) were significantly lower in microcosms containing P. lanceolata than in those containing T. pratense. However, earthworm performance was not affected by AMF, and plant root mycorrhization was not modified by earthworms. Although AMF effectively competed with T. pratense for soil N (as indicated by δ¹⁵N analysis), AMF enhanced the productivity of T. pratense considerably by improving P availability. Remarkably, we found no evidence for interactive effects of earthworms and AMF on the performance of the plant species studied. This suggests that interactions between earthworms and AMF likely are of minor importance.     

Earthworm populations in a northern U.S. Cornbelt soil are not affected by long-term cultivation of Bt maize expressing Cry1Ab and Cry3Bb1 proteins

Earthworms, which play a key role in biogeochemical processes in soil ecosystems, could be negatively affected by the cultivation of transgenic Bt crops. Studies to date have found few effects of Bt maize on earthworm species. If adverse effects occur, they are likely to be chronic or sub-lethal and expressed over large spatial and temporal scales. Our objective in the present study was to investigate potential effects on earthworm populations in soil cultivated with Bt maize in a large multiple-year field study. We surveyed the earthworm populations in 0.16-ha experimental field plots of two varieties of Cry1Ab Bt maize, one variety of Cry3Bb1 Bt maize, and three non-transgenic control varieties cultivated for four years. Four earthworm species were found in our sample: Aporrectodea caliginosa, Aporrectodea trapezoides, Aporrectodea tuberculata (collectively, the A. caliginosa species complex), and Lumbricus terrestris. We found no significant differences in the biomass of juveniles and adults for all four species between Bt and non-Bt maize varieties. From this and previous studies, we conclude that the effects of Cry1Ab and Cry3Bb1 Bt maize on the A. caliginosa species complex and L. terrestris are small. Nonetheless, general conclusions about the effects of Bt maize on earthworm populations are not warranted due to the small number of species tested. In future laboratory studies, earthworm species should be selected according to their association with a Bt crop and the impact of that species to valued soil ecosystem processes.     

Potential of the Silpho Moor experimental birch plots as a habitat for Lumbricus terrestris

It is argued that the podzol of Silpho Moor could be converted under birch to a typical brown earth only if it could sustain an earthworm population with a Lumbricus terrestris biomass of not less than 100 g m^?2. No worms of this species were found under experimental birch plots 30 yr old. The presence of podzolizing species in the ground vegetation; the low pH of the raw humus layer; the low Ca and N supply in the soil, litter and rainfall; and the impeded soil drainage lead to the conclusion that colonization by L. terrestris is unlikely.     

Nutrient content of earthworm casts influenced by different mulch types

The aim of this study was to investigate the effects of different mulch types on the quality and quantity of casts of different lumbricid earthworm species. Nutrient contents (organic carbon C_org, total nitrogen N_t and inorganic phosphate Pi), and acid phosphatase activity (SPA) of earthworm casts and soil aggregates were measured and then compared. This short time experiment was conducted in the laboratory, simulating field conditions of mulch management in temperate agroecosystems. In microcosms, the two common field species Lumbricus terrestris and Octolasion cyaneum were inoculated. Barley, lupin, maize, or sugarbeet were used as mulch according to amounts usually applied in the field. Nutrient contents and phosphatase activity in worm casts were generally enhanced compared to the soil. Nutrient values were higher in the casts of the detritivorous L. terrestris than those of the geophageous O. cyaneum. Conversely, the phosphatase activity was increased in the casts of O. cyaneum compared to L. terrestris in case of the barley and sugar-beet treatments. Cast production was related to the earthworms' change of biomass (ΔB) as well as, in the case of L. terrestris, to nitrogen content of the mulch. Due to their chemical compounds, the mulch types influence both the food selection of the worms and the acceptance by microorganisms.     

The effects of earthworms on the demography of annual plant assemblages in a long-term mesocosm experiment

Earthworms have been shown to influence plant growth, survival and fecundity. They can therefore affect plant demography in plant communities changing their composition. A long term mesocosm experiment was set-up to test the effects of an endogeic (Aporrectodea caliginosa) and an anecic (Lumbricus terrestris) earthworm species on assemblages of four species of annuals: one grass (Poa annua), two forbs (Veronica persica and Cerastium glomeratum) and one legume (Trifolium dubium). The number of individuals and the biomass of each species were investigated. A. caliginosa and L. terrestris affected the density of T. dubium at each of the three monitored census dates. The other plant species responded to A. caliginosa and L. terrestris at the second and third generations. The presences of A. caliginosa and L. terrestris reduced the total number of plant individuals from the second to the third generation. At harvest (3rd generation), T. dubium and V. persica had more and larger individuals in the presence of A. caliginosa. When both earthworm species were present, T. dubium had few but larger individuals. Our study confirms that earthworms affect plant demography and plant community structure. Our results also show that accurate prediction of long-term effects of earthworms on plant communities cannot be achieved using results on their short-term effects on plant growth. This is due to the poor understanding of the effects of earthworms on plant resource allocation and demography, and also the possibility that earthworms may exert the opposite effect on the short and long-term availability of nutrients.     

Short rotation forestry – Earthworm interactions: A field based mesocosm experiment

Short rotation forestry (SRF) which consists of planting rapidly growing native and non-native tree species has been introduced to the UK to increase woody biomass production. A largely unknown aspect of SRF species is their interaction with soil fauna, of which the earthworm community is a major component. Earthworms have a pronounced impact on litter decomposition, nutrient cycling and tree growth. Conversely, tree litter and root chemistry can impact on the associated earthworm community development. The aim of this study was to determine direct interactions between SRF species and earthworms. A field-based mesocosm experiment was conducted using Betula pendula (birch) and Eucalyptus nitens (eucalyptus) with two earthworm species Lumbricus terrestris and Allolobophora chlorotica. The one year experiment revealed that native birch and non-native eucalyptus had a similar influence on L. terrestris population development. However, birch had a positive impact on A. chlorotica population establishment compared with eucalyptus. In the presence of earthworms, total tree biomass and leaf nitrogen concentration of eucalyptus were increased respectively by 25% and 27% compared with an earthworm-free control. In the presence of earthworms, surface litter incorporation was greater for both tree species (almost 5 times for birch and 3 times for eucalyptus) compared with controls. This work showed direct SRF-earthworm interactions which differed for tree species.     

Cultivation of transgenic cyanophycin-producing potatoes does not negatively affect growth,reproduction and activity of the earthworm Lumbricus terrestris (L.)

A microcosm experiment was performed to investigate the effects of post-harvest potato tubers from transgenic cyanophycin-producing potatoes on Lumbricus terrestris (L.) activity and biomass, number of cocoons and their hatchability as well as the remaining cyanophycin content in soil and cast samples during a period of 80 days. Potato tubers from four transgenic potato events with different cyanophycin content in a range from 0.8 to 7.5% were compared to the near isogenic, non-transgenic control (Solanum tuberosum L. cv. Albatros) and a comparative potato cultivar (S. tuberosum L. cv. Désirée). One treatment with transgenic tuber residue but without earthworms was prepared as an additional control. Potato tuber loss from the surface of the microcosms was significantly higher in the treatments with transgenic potato tubers compared with non-transgenic treatments. It can be estimated that the earthworm contribution to potato tuber loss from the soil surface was approximately 61%. Mean number of cocoons in addition to the number of hatched cocoons varied from 2.6 to 6.2 and from 7 to 15 accounting for 45.2–83.35% hatchability, respectively, but no significant differences between the treatments were found. The same was true for the development of earthworm biomass in the various treatments. The cyanophycin content in soil samples was significantly higher when earthworms were present indicating that the cyanophycin content in the upper soil layer might have been enhanced through earthworm burrowing activity. Overall, it is concluded that tubers from transgenic cyanophycin potatoes are easily degradable and neither inhibit nor stimulate earthworm growth, reproduction, and activity.     

Dietary cobalt supplements and the growth and reproduction of the earthworm Eisenia foetida

The effect of adding cobalt, as ⁶⁰Co, to the food source of the earthworm Eisenia foetida was studied. Cobalt was retained with a half-life of 387 ± 43 (SD) days in the worm. After 172 days more cobalt was concentrated in the gut than the body wall. ⁶⁰Co was not transmitted from adults to cocoons. Prolonged studies involving the addition of CoCl₂ (0, 8.2, 16.5 and 82.5 μg Co g^?1) to a food source low in Co indicated that total Co concentrations of 17.6 and 25.9 μg g^?1 resulted in significantly increased maximum weights compared to the control worms which were exposed to 9.4 μg Co g^?1. The highest Co addition (82.5 μg g^?1, total 91.9 μg g^?1) caused no increase in maximum weight over controls, but resulted in a statistically significant lag in early growth compared to that of all other groups. Significantly more cocoons were produced by worms fed 17.6 or 25.9 μg Co g^?1 compared with those fed 9.4 or 91.9 μg Co^?1 Co.     

Non-native anecic earthworms (Lumbricus terrestris L.) reduce seed germination and seedling survival of temperate and boreal trees species

Recent studies have shown that the introduction of non-native earthworms in previously earthworm-free soils may have negative impacts on the recruitment of certain understory plant species in northern temperate forests. There is a need, therefore, to understand the mechanisms that may underlie this phenomenon. A microcosm study was conducted to test the effects of the anecic earthworm, Lumbricus terrestris L., on the number of days for germination, % seed germination, seedling survival and seedling biomass of 14 tree species native to southern Quebec (Canada). Seeds of these species were germinated and grown in the presence or absence of L. terrestris. The presence of earthworms significantly reduced % seed germination of seven tree species, as well as seedling survival of three tree species. The germination date of three tree species was significantly affected, either positively or negatively, by the presence of earthworms. Earthworms had no effect on seedling biomass. Results suggest that the introduction of L. terrestris into forested ecosystems of southern Québec may potentially alter overstory composition through several mechanisms that differentially affect the recruitment of various tree species in the understory.     

Food quality affects production of Lumbricus terrestris (L.) under controlled environmental conditions

Birch leaves and horse manure were used to determine the effects of food quality on growth and reproduction of laboratory-reared Lumbricus terrestris. Animals grew to maturity within 6 months but attained a significantly (p < 0.001) larger adult size with manure (6.17 g) versus leaves (4.20 g). Cocoon production by recently-mated adults maintained in isolation, fed with birch leaves or horse manure, resulted in 4.53 and 3.84 cocoons ind.⁻¹ month⁻¹ respectively, with an initial hatchability of 86%, falling to zero after 18 months. Re-mating of these known individuals permitted long term monitoring of reproductive output (to 30 months). For the whole experimental period, overall hatchability of the 2010 cocoons produced was 44.4%. Median incubation time of those cocoons that hatched within accepted norms (less than 5 months at 15 °C) was 103 days and was not influenced by adult food type. A proportion (35.5%) of cocoons took in excess of 12 months to hatch. Adult mortality was minimal (25%) during the long term experiment but abnormal cocoon production was recorded after 2 years. Overall results demonstrate that food quality can have a significant influence on somatic and reproductive production of L. terrestris and these data may aid construction of production models for this earthworm in ecosystems with contrasting food quality.     

Effects of Lumbricus terrestris, Allolobophora chlorotica and Eisenia fetida on microbial community dynamics in oil-contaminated soil

Oil spills are one of the most common types of soil pollution. Bioremediation has become an attractive alternative to physicochemical methods of remediation, where feasible. Earthworms have been shown to stimulate the degradation of petroleum hydrocarbons in soil, and it was hypothesized that the role of earthworms in remediation lies in the enhancement of an oil degrading microbial community. The aim of this study was to characterize microbial activity and community dynamics in oil-contaminated soil incubated with or without earthworms. Three earthworm species (Eisenia fetida, Allolobophora chlorotica and Lumbricus terrestris) were incubated in crude oil polluted soil (ca. 10,000 mg/kg total petroleum hydrocarbons (TPH)) and a reference soil for 28 d. Control treatments with manual mixing and/or cattle dung amendment were also included. In the oil-contaminated soil, respiration and concentration of microbial biomass was significantly enhanced by earthworm amendment, and TPH concentrations decreased significantly. These effects were less evident in treatments with A. chlorotica, possibly due to a difference in behavior, since individuals of this endogeic species were found in a state of inactivity (aestivation). Microbial community dynamics were described by phospholipid fatty acid (PLFA) analyses. After 28 d, similar shifts in the soil PLFA composition were observed in the oil-contaminated soil irrespective of worm species. Fungal:bacterial ratios were increased in the presence of worms, but also by addition of dung as a food source, indicating a non-specific effect of metabolizable substrates. In contrast, the fatty acids 17:1ω8 (=Δ9-heptadecenoic acid) and 20:4ω6c (arachidonic acid) were specifically stimulated by the presence of earthworms in the oil-contaminated soil. The results showed that earthworms can contribute positively to bioremediation of oil-contaminated soil, but that the effect may be species-dependent.