Earthworm Ingestion Research Articles

Quantifying earthworm soil ingestion from changes in vertical bulk density profiles

Soil mixing by earthworms can have a large impact on the fate of nutrients and pollutants and on the soil's ability to sequester carbon. Nevertheless, methods to quantify earthworm ingestion and egestion under field conditions are largely lacking. Soils of the Fennoscandian tundra offer a special possibility for such quantifications, as these soils commonly lack burrowing macrofauna and exhibit a well-defined O horizon with low bulk density on top of a mineral soil with higher density. Since ingestion-egestion mixes the two soil layers, the temporal changes in the bulk density profile of such soils may be useful for estimating field ingestion rates. In this study, we applied a model for earthworm burrowing through soil ingestion to observed changes in soil densities occurring in a mesocosm experiment carried out in the arctic during four summers with intact soil. The earthworms present in the mesocosms were Aporrectodea trapezoides, Aporrectodea tuberculata, Aporrectodea rosea, Lumbricus rubellus and Lumbricus Terrestris (fourth season only). We show that changes in soil density profiles can indeed be used to infer earthworm ingestion rates that are realistic in comparison to literature values. Although uncertainties in parameter values were sometimes large, the results from this study suggest that soil turnover rates and endogeic earthworm soil ingestion rates in tundra heath and meadow soils may be as high as those reported for temperate conditions. Such large ingestion rates can explain observed large morphological changes in arctic soils where dispersing earthworms have resulted in complete inmixing of the organic layer into the mineral soil. Our approach is applicable to soil profiles with marked vertical differences in bulk density such as the soils of the Fennoscandian tundra where earthworms are currently dispersing into new areas and to layered repacked soil samples that are incubated in the field.

Impacts of microplastics and heavy metals on the earthworm Eisenia fetida and on soil organic carbon, nitrogen, and phosphorus

Microplastics (MPs) are increasingly being studied because they have become ubiquitous in aquatic and terrestrial environments. However, little is known about the negative effects of co-contamination by polypropylene microplastic (PP MPs) and heavy metal mixtures on terrestrial environment and biota. This study assessed the adverse effects of co-exposure to PP MPs and heavy metal mixture (Cu2+, Cr6+, and Zn2+) on soil quality and the earthworm Eisenia fetida. Soil samples were collected in the Dong Cao catchment, near Hanoi, Vietnam, and analyzed for changes in extracellular enzyme activity and carbon, nitrogen, and phosphorus availability in the soil. We determined the survival rate of earthworms Eisenia fetida that had ingested MPs and two doses of heavy metals (the environmental level - 1 × - and its double - 2 ×). Earthworm ingestion rates were not significantly impacted by the exposure conditions, but the mortality rate for the 2 × exposure conditions was 100%. Metal-associated PP MPs stimulated the activities of β-glucosidase, β-N-acetyl glucosaminidase, and phosphatase enzymes in soil. Principle component analysis showed that these enzymes were positively correlated with Cu2+ and Cr6+ concentrations, but negatively correlated with microbial activity. Zn2+ showed no correlation with soil extracellular enzyme activity or soil microbial activity. Our results showed that co-exposure of earthworms to MPs and heavy metals had no impact on soil nitrogen and phosphorus but caused a decrease in total soil carbon content, with a possible associated risk of increased CO2 emissions.

Soil grit influences the effects of earthworms (Lumbricus terrestris) on seed damage

Ingested soil grit is thought to enhance the grinding action of the earthworm gizzard but its role in earthworm-seed interactions is unknown. This study used feeding trials to investigate how different levels of supplemental soil grit (+0 %, +25 %, and +50 % sand additions by weight) influenced the impacts of the cosmopolitan anecic earthworm Lumbricus terrestris L. on seed ingestion, egestion, seed coat damage, and germination of garlic mustard (Alliaria petiolata). Added grit increased the amount of seed coat damage on garlic mustard seeds egested by L. terrestris. Earthworm egestion also increased the speed of garlic mustard germination (∼20 days control, ∼14 days with L. terrestris and +0 % grit, ∼11 days with L. terrestris and +25–50 % grit). The results demonstrate how earthworm ingestion and soil grit can modify the impacts of earthworms on seeds and highlight the importance of considering soil texture in field and laboratory earthworm experiments.

First detection and low prevalence of Pearsonema spp. in wild raccoons (Procyon lotor) from Central Europe.

The urinary bladder and lower urinary tract of domestic and wild carnivores can be parasitised by filamentous nematodes from the genus Pearsonema (syn. Capillaria). Infestations are often asymptomatic, but severe courses in dogs and cats have been described. Hosts are infested through the ingestion of earthworms (Lumbricidae) which act as intermediate hosts. Epidemiological studies of Pearsonema in raccoons (Procyon lotor) in North America are scarce and previous studies of urinary bladder parasites of European raccoons did not provide evidence of infestation. We examined urine sediment or rinse water from urinary bladders of 499 wild raccoons from Luxembourg, Poland and five study sites in Germany. Pearsonema eggs were found in the urine sediment of 31 (6.2%) raccoons. Infested animals were found in all study areas with prevalence values ranging from 3.7% to 8.7%. No significant difference in prevalence was found either between animals in urban and rural areas or between sexes and age classes. Based on their morphology, the eggs were likely to be P. plica. Considering their increasing density in Central Europe, raccoons may play a previously overlooked role in environmental contamination with Personema eggs.

The contribution of earthworms to carbon mineralization during vermicomposting of maize stover and cow dung

Vermicomposting is an eco-friendly way to manage agricultural wastes. Maize stover and cow dung were used as the substrates. Earthworm ingestion and respiration models were employed to quantify earthworm contributions to carbon mineralization. Decreased substrate C/N and slightly increased earthworm tissue C/N were observed. Earthworm biomass carbon first increased and then decreased. Bacterial biomass carbon decreased, while fungi increased and maintained a steady level until the end of the experiment. Bacteria dominated throughout the process. The earthworm feeding rate showed a decreasing trend. In the early, middle and later stages, earthworms directly led to carbon mineralization rates of 0.030, 0.032 and 0.023 g C m−2 month−1, and indirectly led to 0.197, 0.211 and 0.153 g C m−2 month−1, respectively. It indicated that the driving force exerted by earthworms on microbes was more important. This study provides some new insights into the quantification of earthworm contributions to carbon mineralization during vermicomposting.

Novel bioavailability-based risk assessment of Cd in earthworms and leeches utilizing in vitro digestion/Caco-2 and MDCK cells.

In the present study, the oral bioavailability of cadmium (Cd) in earthworms and leeches was investigated through in vitro physiologically based extraction test (PBET) digestion/Caco2 and MDKC cell models. We are the first to create an innovative assessment strategy which has capacity to offer a more precise evaluation of Cd-associated health risks in traditional animal medicines (TAMs), by combinational usage of bioavailable Cd levels, the duration and frequency of the exposure to TAMs obtained by questionnaire data, as well as safety factor of TAMs. Our data showed that the percentage of bioavailability for Caco-2 cells in earthworms and leeches ranged from 3.29 to 14.17% and 4.32 to 12.61%, respectively. The percentage of bioavailability of MDCK cells in earthworms and leeches ranged from 4.83 to 15.74% and 6.53 to 15.04%, respectively. After adjusting by the bioavailability of Cd to target hazard quotient (THQ), excitingly, our findings manifested that the health risks induced by the ingestion of earthworms and leeches were acceptable in the clinic. Our key findings suggest that bioavailability characterization cannot be ruled out and health risks should be assessed on the basis of the bioavailable Cd levels rather than total levels. Our novel strategy provides insight into the bio-accumulation of Cd in organisms as well as a more realistic and accurate assessment of Cd-associated health risks in TAMs, with the main purpose of improving public health by scientifically using TAMs.

Arsenic speciation in titanium dioxide (TiO2) waste produced via drinking water filtration: Potential environmental implications for soils, sediments, and human health

Arsenic (As) contamination in soil and water is a global human health and environmental problem due to its common occurrence and high toxicity. At least four million people in Latin America have long-term exposure to As in drinking water. In northwestern Costa Rica, As has been measured in drinking water at concentrations ranging from 20 to over 80 µg As L−1. Arsenic contaminated drinking water can be treated using filter technologies; titanium dioxide (TiO2)-based drinking water filters decrease As concentration and help mitigate As exposure. However, this process creates an As-enriched TiO2 solid-phase waste product. An objective of this study is to determine the chemical forms of As in this waste product, which is commonly distributed on soil surfaces and throughout urban and rural areas adjacent to drinking water treatment facilities in the sample area. An additional objective is to determine biogeochemical changes in As speciation in filter waste and affected soils which may be induced through earthworm ingestion, which also occurs in the sample area. Arsenic concentrations in the solid-phase filter waste were measured to be up to 600 mg kg−1. There was a strong correlation between As and Ti (R2 > 0.90) indicating As accumulates within or on the surface of the TiO2 mineral. Earthworm castings enriched in TiO2 contained up to 530 mg As kg−1, which provided direct evidence soil macroorganisms ingest filter waste. X-ray diffraction (XRD) confirmed Ti is predominantly anatase with minor amounts of quartz and feldspar. These results are novel and innovative because they identify and characterize a previously unexplored problem of anthropogenic soil and sediment As contamination and redistribution in urban and rural environments. Additionally, dry windy seasons in the region increase potential risk of As and TiO2 exposure through dust inhalation. Earthworm consumption did not decrease As concentrations in earthworm castings. Synchrotron-based X-ray absorption spectroscopy (XAS), specifically X-ray absorption near edge structure (XANES) spectroscopy, indicated the dominant species of As in soil and sediment samples was arsenate [As(V)], which is similar to the chemical form of As in the groundwaters of this region. No evidence of arsenite [As(III)] was identified in any of the solid-phase samples, including earthworm castings.

Urinary capillariosis in dogs

Background. Urinary capillariosis in dogs is caused by Capillaria plica (syn. Pearsonema plica), a ubiquitous parasitic nematode resembling a string which belongs to the family Capillariidae. It parasitizes the feline, canine and musteline urinary bladder, and has been found in ureters and renal pelvises as well. C. plica has an indirect life cycle, with earthworms (Lumbricina) as intermediate hosts and domestic and wild animals (dog, cat, fox and wolf) as primary hosts. Infection of primary hosts occurs via ingestion of earthworms that contain infective first stadium (L1) larvae. An alternative path of infection for primary hosts is assumed to be ingestion of soil contaminated by infectious larvae derived from decomposed earthworms. Infection is mostly asymptomatic, but the clinical picture presents with pollakiuria, dysuria, haematuria, polydipsia, incontinence and/or fever. Scope and Approach. The aim of this review is to highlight the importance of urinary capillariosis in dogs. Since the health care of wild and domestic carnivores is extremely important, this review provides information about the morphology, biology and epizootiology of the C. plica nematode. Due to the importance of this disease for clinicians and increased disease prevalence during the last decade in many countries, this review presents the latest information on the pathogenesis, clinical signs, diagnosis, treatment and prevention of this infection. Key Findings and Conclusions. Capillariosis is usually accidentally diagnosed due to the nonspecific clinical signs and there is no treatment of choice. Practitioners should consider latent urinary capillariosis infection as a possible cause while examining for urinary tract diseases.

Short-term carbon mineralization from endogeic earthworm casts as influenced by properties of the ingested soil material

Fresh casts of endogeic earthworms are considered a hotspot of microbial activity that exhibit greater carbon mineralization (Cmin) than the bulk soil. While cast properties depend on the ingested soil material, little is known about how earthworm feeding behavior and digestive processes interact with those properties to determine the Cmin in fresh casts egested by endogeic earthworms. Two laboratory experiments were designed to (i) assess the short-term changes in Cmin of soil and fresh casts after the soil or soil physical size fractions passed through the gut of Aporrectodea caliginosa, a common endogeic species in temperate agroecosystems, and (ii) to determine whether these changes depended on initial properties of the ingested materials. In the first experiment, we determined how Cmin was affected by gut passage (i.e., casts vs. bulk and surrounding soil) and soil type (three sandy-loam soils with variable content of light fraction organic matter (LF): the Courval, St. Amable and Chicot soil series). In the second experiment, we related Cmin in casts to the interactive effect of the gut passage and soil fraction size (Courval soil series only). Six soil treatments were examined: whole soil and five-soil fraction size classes (2000–1000μm, 1000–500μm, 500–250μm, 250–53μm and <53μm). As hypothesized, the earthworm gut transit increased Cmin in casts by two to three-fold relative to the bulk soil and surrounding soil, and the increase in cast Cmin was soil- and soil fraction size-specific. The Cmin in casts was significantly (p<0.05) greater in the finest soil fraction (<53μm) and lowest in the intermediate fraction (500–250μm) compared to the whole soil and other soil fractions. Additionally, the priming effect of earthworm ingestion and digestion processes, estimated by the normalized Cmin for casts (which subtracts the baseline Cmin flux from the bulk soil or soil fraction) was positively correlated (p<0.05) with the C concentration of the LF in the ingested soil. This suggests that A. caliginosa derive their nutrition from the LF, and that the 500–250μm fraction is the optimal size to support their nutritional requirements.

Addition of cattle manure to sheep bedding allows vermicomposting process and improves vermicompost quality

Animal waste is usually a good substrate for vermicomposting. However, numerous animal husbandry systems use bedding that consists primarily of lignocellulosic substrates, which hinders earthworm and microorganism’s development and thus, the entire bioconversion process. One possible solution is to mix the used bedding with other waste materials that are more amenable to earthworm ingestion and can provide better conditions for earthworm population growth. Here, we have aimed to examine the effectiveness of such procedure by mixing rice-husk-based sheep bedding with cattle manure in different proportions (0%, 25%, 50%, 75% and 100%). We have carried out vermicomposting experiments in benchtop vermireactors inoculated with 0.88kg of dry matter (sheep bedding+cattle manure). Data used in the Principal Component Analysis were the multiple vermicomposting variables (i.e., EC; pH; HA/FA and C/N ratios; P, K, cellulose, and hemicellulose content). The effect of the treatment on earthworm count was analyzed with ANOVA. We have observed that the addition of at least 25% of cattle manure to sheep bedding allows vermicomposting process but it is necessary 148days to obtain a stabilized vermicompost. However, increasing the proportion of cattle manure to sheep bedding, the vermicomposting time decreases proportionally to 94days. We concluded that vermicomposting can be considered a bioprocess to stabilize rice husk after being used as sheep bedding.

Microbial community structure and metabolic property of biofilms in vermifiltration for liquid-state sludge stabilization using PLFA profiles

To investigate effects of earthworms on microbial community structure and metabolic properties of biofilms in vermifiltration for liquid-state sludge stabilization, a vermifilter (VF) with earthworms and a conventional biofilter (BF) without earthworms were compared. The Shannon index of fungi in VF was 16% higher than that in BF, which indicated earthworm activities significantly enhanced fungi diversity. The ratio of monounsaturated to saturated (mono:sat) PLFAs of VF biofilms was higher than that of BF biofilms, which indicated the physiological and nutritional stress for microbial community in VF was relieved due to the increasing of soluble substances caused by the earthworm ingestion. Further investigation showed that the burrowing action of earthworms promoted the aeration condition and led to aerobic microorganisms were predominant in VF. Those results indicated earthworms improved microbial community structure and metabolic properties of biofilms and thus resulted in the overall optimization of the vermifiltration system for liquid-state sludge stabilization.

Native and exotic earthworms affect orchid seed loss

Non-native earthworms have invaded ecosystems around the world but have recently received increased attention as they invaded previously earthworm-free habitats in northern North America. Earthworms can affect plants by ingesting seeds and burying them in the soil. These effects can be negative or positive but are expected to become increasingly negative with decreasing seed size. Orchids have some of the smallest seeds of any plants, so we hypothesized that earthworm consumption of seeds would decrease seed viability and lead to burial of ingested seeds. We used a combination of mesocosms and field measurements to determine whether native and non-native earthworms would affect Goodyera pubescens seed germination by decreasing seed viability through digestion or burial. To determine soil depths at which seed burial would decrease chances of germination, we used field measurements of the abundance of mycorrhizal fungi needed for G. pubescens ger- mination at different soil depths. We found that the combined effects of earthworm ingestion and burial would be expected to result in a loss of 49 % of orchid seeds in mature forests and 68 % of those in successional forests over an average year. Differences in seed ingestion and burial among soils from mature and successional forests were probably driven by differences in their ability to support earthworm biomass and not by differences in earthworm behaviour as a function of soil type. The combined effects of earthworm ingestion and burial have the potential to result in substantial loss of orchid seeds, particularly in successional forests. This effect may slow the ability of orchids to recolonize forests as they proceed through succession. Determining whether this strong effect of earthworms on G. pubescens viability and germination also applies to other orchid species awaits further testing.

High prevalence of Capillaria plica infections in red foxes (Vulpes vulpes) in Southern Germany

The nematode Capillaria plica is an ubiquitous parasite of the urinary tract of Canidae and Felidae. It causes a wide spectrum of clinical symptoms, ranging from asymptomatic infections to urinary bladder inflammation, pollacisuria, dysuria, and hematuria. Foxes serve as reservoir hosts and are considered to be a potential source of infection for companion and hunting dogs as well as domestic cats which acquire the infection by ingestion of earthworms which are the intermediate hosts. Despite its importance, epidemiological studies on this parasite are scarce and almost entirely lacking altogether for Central Europe. Therefore, we examined 116 red foxes (Vulpes vulpes) for the infection of C. plica by pathologic examination of the urinary bladders and microscopy of mucosal smears and urine sediments. The parasite was detected in 90 (78%; 95% CI, 68.9-84.8%) of the foxes, originating from all administrative districts of Bavaria (Southern Germany). Since Bavaria is characterized by a high number of forests and wildlife sanctuaries that provide ideal living conditions for foxes, the corresponding risk of infection of companion and hunting dogs by oral ingestion of earthworms as the intermediate hosts can likewise not be excluded. Because of the scarcity of reports on prevalences of C. plica worldwide, we also include a brief review of the available literature.

Modification of P availability by endogeic earthworms (Glossoscolecidae) in Ferralsols of the Malagasy Highlands

Low phosphorus (P) availability in Ferralsols of the Malagasy Highlands is a major limitation to crop growth. Direct seeding mulch-based cropping practices which were adopted in the region to improve and sustain soil fertility are known to favour earthworms’ presence. The mesocosm study aims to analyse the effect of an endogeic geophageous earthworm species on the soil P status. Total P content (P t), NaOH-extractable P content, P ions (Pi) concentration (C p) in solution and rapid and slow reactions of Pi in solution with solid phase were determined in two Malagasy Ferralsols. Both C p and reactions rates were assessed in laboratory batch experiments using 32Pi labelling and isotopic exchange kinetics (IEK). The P t values were 836 and 349 mg P g−1 in a clayey soil and a sandy–clayey soil, respectively. For both soils, NaOH-extractable organic P was significantly higher in earthworm casts than in parent soils, whereas Pt was unchanged. Also, the effect of earthworm ingestion significantly changed parameters of the IEK. In casts compared with the soil from which they were derived, the immediate isotopically exchangeable Pi (E 1 min) increased by 116%, whereas relative rates of Pi release at the solid-to-solution with time were slightly lowered. The effect of earthworm ingestion on IEK corresponded to a transfer of slowly exchangeable Pi towards quicker Pi pools of exchange. However, according to the literature, the increase in E 1 min remained below the critical level for optimal growth, stating that the soils remained P-deficient even in the presence of active and numerous earthworms.

The role of different organic wastes on zinc bioaccumulation by earthworm Lumbricus terrestris L. (Oligochaeta) in successive Zn added soil

Organic matter strongly adsorbs zinc and is also the preferred food of the earthworm Lumbricus terrestris. Earthworms have the potential to accumulate significant levels of zinc, and thus earthworm ingestion may result in zinc transfer to higher trophic levels (e.g. various birds and small mammals). This study examines the zinc bioaccumulation by earthworm L. terrestris and Zn contents in casts due to ingestion of different organic wastes in successive doses of Zn (0, 50, 100, 250, 500, and 1000 μg g −1) added soil. Twenty-one days after organic wastes treatment, the cast and earthworm bodies receiving the highest Zn dose showed significantly higher Zn content than the non-treated soil. At all Zn doses, earthworms from soils treated with organic wastes of high C/N ratio (wheat straw and hazelnut husk) had the highest Zn concentrations. In addition, the lowest bioaccumulation factor (BAF) value occurred in low C/N ratio of organic wastes (tea and tobacco production waste). Furthermore, except for the 0 μg Zn g −1 doses, the highest BAF value occurred in 100 μg Zn g −1 at all organic waste treatment soils.

Influence of nematophagous fungi, earthworms and dung burial on development of the free-living stages of Ostertagia ( Teladorsagia) circumcincta in New Zealand

Biological options for nematode parasite control are being sought, as the long-term efficacy of conventional anthelmintics comes increasingly under threat from drug-resistant parasites. Three biological methods with the potential to reduce pasture contamination by parasitic nematode larvae were examined: (a) killing of larvae developing in dung by nematophagous fungi; (b) removal of dung through earthworm ingestion; (c) burial of dung in soil as might occur through the action of dung beetles. Field trials with the test bio-control agents were carried out in autumn and spring by adding dung from sheep infected with Ostertagia ( Teladorsagia) circumcincta to pots of ryegrass/white clover. The factorial treatment structure included five fungal treatments (individual applications of Duddingtonia flagrans, Monacrosporium gephyropagum and Harposporium helicoides, a combination of all the three fungi together and an untreated control), two dung burial treatments (dung buried or deposited on the soil surface) and two earthworm treatments (earthworms present or absent). D. flagrans and H. helicoides, individually or in combination, reduced recovery of infective stage larvae in experiment 1, while only H. helicoides reduced recovery in experiment 2. In both the experiments, dung burial increased the total number of larvae recovered, while the number of infective larvae were reduced by the action of earthworms. Increased recovery following burial, along with the fact that larvae moved rapidly from soil onto herbage, suggests that soil may provide a protective reservoir for infective larvae infesting herbage.

Diazinon dissipation from vegetation, occurrence in earthworms, and presence in avian gastrointestinal tracts collected from apple orchards following D‐Z‐N® 50W application

AbstractComprehensive residue determinations weremade in biota inhabiting orchards receiving diazinon application as part of ecotoxicology studies in the United States. The states of Washington and Pennsylvania served as study areas representing different climatic and agricultural practices. Mean diazinon application was 3.0 to 3.1 kg a.i./ha in the orchards, and a subsequent exponential reduction in concentrations occurred on vegetation. Diazinon was present in earthworms following application, and 23 of 25 avian species evaluated in treatment orchards contained diazinon in their gastrointestinal (GI) tracts. Diazinon residues were present in 18 of the 20 avian species that were represented by more than one sample. Quantifiable residues were present in 17 of the bird species. Earthworms from Pennsylvania orchards contained more frequent and higher diazinon concentrations than did earthworms from Washington orchards (p &lt; 0.005). Passerine exposure to diazinon was not different when comparing diazinon concentrations in individual species between the two geographic regions (0.23 &lt; p &lt; 0.06). Exposures were different for American robins and European starlings (p = 0.03) in Washington and for Northern cardinals and European starlings (p = 0.03) in Pennsylvania. Residues in GI tracts suggest that lethal exposures were limited to the day of application and the 4 d following application. Data indicate that, under conditions of repeated diazinon application, ingestion of earthworms poses risks to passerines.

A Comparative Study of Facial Grooming after Prey Ingestion in Colubrid Snakes

For a comparative study of facial grooming behavior, we selected five species of colubrid snakes (Thamnophis sirtalis, T. butleri, T. melanogaster, Storeria dekayi, and Cyclophiops semicarinatus) based upon their phylogenetic relationships and natural diets. In an initial descriptive study, head-rubbing behavior reliably followed ingestion of earthworms in all five species. Three forms of head rubbing were identified, including two forms of labial rubbing and one form of rostral area rubbing. The latter occurs during foraging as well as grooming. Two additional controlled experiments were then performed. One experiment assessed the effects of multiple feedings with either normal or immobilized earthworms. The second tested the effects of allowing snakes to contact surface secretions of earthworms and purified mucin without physically contacting the worm. The snakes showed a significantly greater number of head rubs when consuming active earthworms than when consuming immobilized worms, and this increased over the five trials. The snakes also head rubbed more frequently in response to earthworm mucus than to either earthworm surface wash or diluted mucin. The physical properties of earthworm mucus (adhesiveness) thus seem to stimulate head-rubbing behavior. Differences in head rubbing among the species are discussed in relation to natural diet and phylogenetic relatedness. Furthermore, mouth gaping often occurred with head rubbing and can be distinguished from yawning. Tactile and kinesthetic cues associated with this gaping behavior may aid in regulating the occurrence of head rubbing. Neonate snakes head rubbed in a species-typical manner.

Earthworm effects on selected physical and chemical properties of soil aggregates

Some physical and chemical properties of 1-to 2-mm aggregates obtained from casts and the burrow-wall material of the earthworm species Lumbricus terrestris, Aporrectodea longa, and Aporrectodea caliginosa were determined in order to show the effects of earthworms on the stabilization of soil aggregates. The results were compared with those of the natural soil from the Ap horizon of a Parabraunerde (Luvisol, FAO). Both the tensile strength and the water stability of aggregates from casts and burrow-wall material were reduced compared with those of the natural aggregates but were increased compared with those of remoulded aggregates. These results indicate that to a great extent existing bonds are destroyed by earthworm ingestion. Nevertheless, earthworm activities are advantageous for the stabilization of reformed aggregates. The coarse sand fraction is reduced by selective ingestion by earthworms. The organic C content is increased by 4.1–21.0% for burrow-wall material and by 21.2–43.0% for casts. The carbonate content of aggregates from casts and burrow-wall material of L. terrestris was reduced by more than 50%, while that of A. longa showed no noticeable changes and that of A. caliginosa was increased by more than 60%. The total content of polysaccharides was increased by 35–87% for casts and by 33–46% for the burrow-wall material of all earthworm species. The most frequently detected monosaccharides were glucose, galactose, and glucosamine. L. terrestris appeared to have the strongest effect on the interparticle bonding of the reformed aggregates, measured both as tensile strength and water stability, followed by A. longa and A. caliginosa.

Ingestion of earthworms, Pontoscolex corethrurus, by village pigs, Sus scrofa papuensis, in the highlands of Papua New Guinea

In a short (28-day) experiment, weanling village pigs, Sus scrofa papuensis, gained weight at the rate of 147 g daily when foraging on tethers in harvested sweet potato gardens, Impomoea batatas (L) Lam., and fed additional raw sweet potato tubers. A comparable group of pigs that had no access to soil lost weight and exhibited signs of protein malnourishment. The highly significant difference in growth rate was thought to be due to the foraging pigs consuming earthworms, Pontoscolex corethrurus, which were abundant in the soil. Ten foraging pigs were closely observed over a period of 3 months. Daily weight gains increased to 190 g, and it was recorded that each pig ate between 414 and 1224 earthworms daily (half the daily amount being eaten in the first hour of foraging), and that this activity was predominant. As the day progressed, the pigs spent more time lying down, standing doing nothing, or eating green vegetation. These observations are discussed in the context of local pig husbandry.