Importation of Exotic Ticks into the United Kingdom via the International Trade in Reptiles

Due to the increased trade in exotic reptiles, many of which are infested with ticks of various genera, there is an increased risk of exotic ticks and pathogens being introduced and potentially becoming established in new geographical areas. Despite the number and variety of tick species collected from reptiles, their role in the maintenance of pathogens and transmission to humans has not been fully investigated for all species. The potential public health risks to the United Kingdom have been examined through a preliminary study involving the collection and identification of exotic tick species imported via the reptile trade. Reptiles imported into Heathrow Airport, London (July 2003–October 2004) were carefully examined for ectoparasites. Five species of tick were collected: Aponomma exornatum, Ap. latum, Amblyomma rotundatum, Am. dissimile and Am. nuttalli. This is the first report of Am. dissimile identified from an interception at Heathrow airport. The potential for establishment of exotic ticks in the UK and the public health risks are discussed.     

Ticks parasitizing reptiles in the Bahamas

Two species of reptile ticks, Amblyomma dissimile Koch and Amblyomma torrei Pérez Vigueras (Acari: Ixodidae), are reported from the Bahama Islands for the first time. The widespread neotropical (including the Caribbean and southern Florida) A. dissimile was recovered on Andros Island from three species of reptiles all for the first time: the Andros iguana Cyclura cychlura cychlura Cuvier, the Andros curly tail lizard Leiocephalus carinatus coryi Schmidt, and the Andros boa Epicrates striatus fowleri Sheplan and Schwartz. The iguana tick A. torrei, previously known only from Cuba, Puerto Rico and the Cayman Islands, was recovered in the Exuma Islands from the Exuma iguana Cyclura cychlura figginsi Barbour. Mean numbers of ticks per host were as high as 36.6 on Mangrove Cay, Andros Island, and 25.8 on Pasture Cay in the Exuma Islands.     

Introduction of potential heartwater vectors and other exotic ticks into Florida on imported reptiles

Following the discovery of establishment of the African tortoise tick Amblyomma marmoreum in Florida, the present study was undertaken to determine the extent of introduction of exotic ticks into Florida on imported reptiles. Exotic ticks were identified on 29 (91%) of 32 reptile premises in 18 counties of Florida. The ticks, found on a variety of imported tortoises, snakes, and monitor lizards, belonged to 4 Amblyomma species (A. marmoreum, Amblyomma nuttalli, Amblyomma sabanerae, and Amblyomma sparsum) and 4 Aponomma species (Aponomma exornatum, Aponomma flavomaculatum, Aponomma latum, and Aponomma varanensis). The most commonly encountered ticks were A. latum and A. marmoreum. The identifications of A. marmoreum on 8 premises in 7 counties, and of A. sparsum on 1 premises, are of great concern because both species are vectors of heartwater, a lethal disease of cattle, sheep, goats, and deer.     

Ticks (Acari: Ixodoidea) in China: Geographical distribution,host diversity,and specificity

Ticks are obligate blood‐sucking ectoparasites, which not only directly damage through bites but also transmit many pathogens. China has a high diversity of tick species, 125 species have been reported, including 111 hard tick and 14 soft tick species. Many of the ticks are important vectors of pathogens, resulting in zoonoses. The dynamics of ticks are affected by both the host and habitat environment. However, systematic studies on the geographical distribution, host diversity, and specificity of ticks are limited in China. To achieve this goal, the relevant available data were summarized and analyzed in this study. Ticks are distributed in all parts of China and Xinjiang has the most records of ticks. The distribution of ticks in adjacent areas is similar, indicating that the habitat environment affects their distribution. Most ticks are widely distributed, whereas some species are endemic to their distributed regions. Ticks are parasitic on mammals, birds, and reptiles, of which mammals are the main host species. Overall, most ticks parasitize different hosts, only a few ticks have strict host specificity, such as ticks that are specifically parasitic on reptiles and bats. In addition, environmental changes and control efforts also influence the dynamics of ticks. These results can better reveal tick biological traits and are valuable for tick control.     

History and Future of Introduction of Exotic Arthropod Biological Control Agents in Spain: A Dilemma?

The first documented introduction of an exotic invertebrate biological control agent (IBCA) in Spain occurred in 1908. Sixty-four additional species have been introduced since then. Information, both previously recorded and original data, on the species introduced for pest control is summarized. Most of the introduced IBCAs focused on citrus pests and homopterans clearly predominate among target phytophagous species. Success has been more frequent for IBCAs used in seasonal inoculative strategies (50.0% of cases) than in classical biological control programs (17.1% of cases). Concerns about potential non-target effects of such species are increasing, but post-release evaluation has often been insufficient to draw any conclusions about them. Most of the beneficial species introduced in Spain were parasitoids (n = 53), and the remaining species were predators (n = 12). Only four parasitoids are considered specialized monophagous natural enemies. The mean number of host species parasitized by parasitoids is 15.2, whereas the mean number of prey species attacked by predators is 21.2. Therefore, polyphagy appears to be quite common among the IBCAs that have been introduced in Spain. The rationale guiding many of these introductions in the past would not be acceptable nowadays. Since classical biological control is such a valuable strategy for pest control, straightforward protocols to evaluate exotic candidate species are urgently needed.     

Ticks (Acari: Ixodidae) parasitizing migrating and local breeding birds in Finland

Ticks are globally renowned vectors for numerous zoonoses, and birds have been identified as important hosts for several species of hard ticks (Acari: Ixodidae) and tick-borne pathogens. Many European bird species overwinter in Africa and Western Asia, consequently migrating back to breeding grounds in Europe in the spring. During these spring migrations, birds may transport exotic tick species (and associated pathogens) to areas outside their typical distribution ranges. In Finland, very few studies have been conducted regarding ticks parasitizing migrating or local birds, and existing data are outdated, likely not reflecting the current situation. Consequently, in 2018, we asked volunteer bird ringers to collect ticks from migrating and local birds, to update current knowledge on ticks found parasitizing birds in Finland. In total 430 ticks were collected from 193 birds belonging to 32 species, caught for ringing between 2018 and 2020. Furthermore, four Ixodes uriae were collected from two roosting islets of sea birds in 2016 and 2020. Ticks collected on birds consisted of: Ixodes ricinus (n?=?421), Ixodes arboricola (4), Ixodes lividus (2) and Hyalomma marginatum (3). Ixodes ricinus loads (nymphs and larvae) were highest on thrushes (Passeriformes: Turdidae) and European robins (Erithacus rubecula). The only clearly imported exotic tick species was H. marginatum. This study forms the second report of both I. uriae and I. arboricola from Finland, and possibly the northernmost observation of I. arboricola from Europe. The importation of exotic tick species by migrating birds seems a rare occurrence, as over 97% of all ticks collected from birds arriving in Finland during their spring migrations were I. ricinus, a species native to and abundant in Finland.

     

The distribution of Hyalomma spp. ticks from domestic ruminants in Iran

The distribution of Hyalomma species on domestic animals was studied in four zoogeoghraphical zones. Nine hundred and ninety-two Hyalomma ticks were collected from sheep, goats, cattle and camels. A total of seven tick species consisting of: Hyalomma anatolicum Koch, 1844 (28.93%), H. excavatum Koch, 1844 (12.5%), H. asiaticum Schulze & Schlottke, 1930 (13.5%), H. marginatum Koch, 1844 (27.01%), H. detritum Schulze, 1919 (9.67%), H. schulzei Olenev, 1931 (4.03%) and H. dromedary Koch, 1844 (4.33%) were recorded. The results indicated that H. anatolicum, H. asiaticum, H. marginatum and H. detritum were present in all zones whereas H. excavatum was absent in Zone I. The result also showed that H. dromedari was presented in Zones III and IV whereas H. schulzei was present in Zones II and III. During this study, the tick species collected are candidates for investigation as vectors of pathogenic organisms in Iran.     

Ticks collected from migratory birds,including a new record of Haemaphysalis formosensis,on Jeju Island,Korea

Migratory birds may disperse parasites across ecological barriers, and recent climate change may alter the pattern of ectoparasite dispersal via changed patterns of bird migration. In order to document the parasitization of migratory birds by Ixodidae ticks on Jeju Island in Korea, we examined 934 migratory birds comprising 75 species for ticks from 2010 to 2012. In total, 313 ticks were collected from 74 migratory birds across 17 avian species and identified based on morphological keys. These ticks represented six species: Haemaphysalis flava, H. formosensis, H. longicornis, H. concinna, Ixodes turdus and I. nipponensis. Of particular note was the presence of H. formosensis, a species not previously reported to have been found in Korea, and H. concinna, which had not been previously reported on Jeju Island. The dominant tick species found were H. flava (226 ticks, 72.2 %) and I. turdus (54 ticks, 17.3 %), and ground-dwelling thrushes such as Pale thrushes (Turdus pallidus; 39 birds, 52.7 %) were the most important hosts. Although H. longicornis is the most abundant and prevalent terrestrial tick on Jeju Island, the species accounted for only 3.8 % of the total ticks collected in this study, suggesting that ticks on migratory birds may differ from the local tick fauna and that exotic ticks may be introduced via migratory birds. Therefore, long-term programs for tick and tick-borne disease surveillance are recommended to understand the role of migratory animals in the introduction of exotic species and associated pathogens and in life cycles of ticks at different stages in this region.     

Recent cases of invasive alien mites and ticks in Japan: why is a regulatory framework needed?

Japan’s economy depends on the importation of natural resources, and as a result, Japan is subjected to a high risk of biological invasion. Although Japan has quarantine systems to protect ecosystems, agriculture, forestry, fisheries, and human health against alien species, economic globalization has resulted in an ever-increasing risk of invasion. Mite invasion is no exception. Alien species that impact natural ecosystems are regulated in Japan by the Invasive Alien Species Act. However, the law focuses only on visibly recognizable species, so that species too small to see, such as viruses, bacteria, fungi, and mites, are beyond the scope of this law. The Plant Protection Law has limited the introduction of alien pests, including mites, that are harmful to agricultural crops. Recently, the liberalization of global trade policies have increased pressure to loosen regulations on various pests, including spider mites. Infectious diseases and their causative species are quarantined under the Rabies Prevention Law, the Domestic Animal Infectious Diseases Control Law, and the Human Infectious Diseases Control Law, but these laws do not cover wildlife diseases. The most serious problem is that wild reptiles, which can be carriers of ticks and tick-borne diseases, can be freely introduced to Japan. These loopholes in Japan’s regulatory system have resulted in mite and tick invasions, which affect not only wildlife communities and human society but also endemism and biological diversity of natural mite populations.     

Reptile trade and the risk of exotic tick introductions into southern South American countries

Ticks exotic for the Neotropical region were found on Python regius imported into Argentina and Chile. All ticks (7 males and 3 females) were classified as Amblyomma latum Koch, 1844 ( = Aponomma latum). Additionally, four lots comprising 18 males of the Argentinean tortoise tick, Amblyomma argentinae Neumann, 1904, were found on a terrestrial tortoise, Chelonoidis chilensis, and on three terrestrial tortoises (probably C. chilensis) imported to Uruguay presumably from Argentina). These findings alert us to the risk of expanding the distribution of reptile parasites and their diseases into regions previously free of these parasites.     

Keeping reptiles as pets in Brazil: Ethnozoological and conservation aspects

Regardless of many legal restrictions, the keeping of and trade in reptiles as pets has been increasing in Brazil over the last few years. We present an analysis of the trade and use of reptiles as pets in Brazil and discuss the implications. Data were obtained through semi-structured questionnaires given to 719 owners, who were contacted through reptile-owner groups on the social network Facebook. A total of 69 reptile species were reported as pets in Brazil, of which there were 39 snakes, 17 lizards, 12 chelonians and 1 species of crocodilian. Of the reported species, 46 are native to Brazil and 23 are exotic, including threatened species. Owners were distributed in at least 24 states, with a higher concentration in Southeast Brazil and the Federal District. Owners usually acquire animals through purchase, although prices vary and are high for some species, making reptile ownership more common among high-income individuals. Prices were affected by factors such as beauty, colour pattern, size, sex and even rarity. The keeping of reptiles as pets raises conservation concerns, as the practice directly impacts exploited populations and is a potential introduction pathway for invasive species, including exotic species that have already been recorded in natural habitats in Brazil. A thorough discussion, encompassing various stakeholders — namely, owners, traders and environmental authorities — is much needed, to address management strategies, and propose feasible solutions. Conservation and animal welfare NGOs should also be involved in this process.     

Isolation and characterization of a novel Borrelia group of tick-borne borreliae from imported reptiles and their associated ticks

The members of the genus Borrelia are transmitted by arthropods and known to be infectious to vertebrates. Here we found isolates and DNAs belonging to the Borrelia turcica and unknown Borrelia species from imported reptiles and their ectoparasites. The Borrelia strains were isolated from blood and multiple organs of exotic tortoises, and were experimentally infectious to captive-bred tortoises. These findings suggest that these tortoises may be a candidate as the reservoir host of the Borrelia species. In this study, the Borrelia strains were also isolated from and/or detected in hard-bodied ticks, Amblyomma ticks and Hyalomma ticks. In some of these ticks, immunofluorescence imaging analysis revealed that the Borrelia had also invaded into the tick salivary glands. Accordingly, these ticks were expected to be a potential vector of the Borrelia species. Sequencing analyses of both housekeeping genes ( flaB gene, gyrB gene and 16S rDNA gene) and 23S rRNA gene-16S rRNA gene intergenic spacer region revealed that these Borrelia strains formed a monophyletic group that was independent from two other Borrelia groups, Lyme disease Borrelia and relapsing fever Borrelia . From these results, the novel group of Borrelia comprises the third major group of arthropod-transmitted borreliae identified to date.     

Risk assessment of potential invasiveness of exotic reptiles imported to south Florida

The recent explosion of exotic reptiles in south Florida requires effective management strategies. The objective of this study is to bring knowledge of ecological correlates and quantitative modeling methods into management by providing the foundation for a screening procedure that will identify potentially invasive species and assess adverse impacts associated with these species. We considered 17 variables and, based on model selection procedures, we identified the following significant predictors of establishment success: taxonomic order, maximum temperature match between a species’ native range and Florida, animal sale price, and manageability (defined as a species’ maintenance cost, aggressiveness, proneness to escape, and venomousness). Applying the models to predict establishment success of 33 reptiles that were most frequently imported through Miami and St. Petersburg ports from 2000 to 2005 and two additional reptiles of concern in Florida, we identified eight lizards and four snakes as potentially successful invaders. We further assessed adverse impacts associated with potential invaders, should they become established, by identifying species that are (1) dangerous to humans, (2) dangerous to the ecosystem (upper trophic-level predators), and (3) rapidly spreading. Controlling exotic reptiles can be expensive and labor intensive once they are established. Information on which species are potential invaders based on screening procedures and what impacts these species might cause will be a valuable contribution to the development of proactive management strategies.     

Acquired immunity to larvae of Amblyomma marmoreum and Ahebraeum by tortoises, guinea-pigs and guinea-fowl

A study of acquired resistance in guinea-pigs, guinea-fowl and tortoises to larvae of the ticks Amblyomma hebraeum Koch and A.marmoreum Koch (Acari: Ixodidae) showed that repeated infestations of the laboratory host resulted in a 29.3-49.4% reduction respectively in weight of engorged larvae. No resistance was induced in guinea-fowl, the natural host for larvae of both species. A small decline in the mean weight of engorged larvae was observed for both species of ticks after three successive infestations on tortoises. The reduction in weight was more pronounced in A.hebraeum (14.5%) which does not naturally feed on tortoises than for A.marmoreum (8.4%), a common tick on this host. The occurrence of acquired resistance in natural tick host relationships as opposed to unnatural tick host relationships is discussed.     

Identification of Hotspots in the European Union for the Introduction of Four Zoonotic Arboviroses by Live Animal Trade

Live animal trade is considered a major mode of introduction of viruses from enzootic foci into disease-free areas. Due to societal and behavioural changes, some wild animal species may nowadays be considered as pet species. The species diversity of animals involved in international trade is thus increasing. This could benefit pathogens that have a broad host range such as arboviruses. The objective of this study was to analyze the risk posed by live animal imports for the introduction, in the European Union (EU), of four arboviruses that affect human and horses: Eastern and Western equine encephalomyelitis, Venezuelan equine encephalitis and Japanese encephalitis. Importation data for a five-years period (2005-2009, extracted from the EU TRACES database), environmental data (used as a proxy for the presence of vectors) and horses and human population density data (impacting the occurrence of clinical cases) were combined to derive spatially explicit risk indicators for virus introduction and for the potential consequences of such introductions. Results showed the existence of hotspots where the introduction risk was the highest in Belgium, in the Netherlands and in the north of Italy. This risk was higher for Eastern equine encephalomyelitis (EEE) than for the three other diseases. It was mainly attributed to exotic pet species such as rodents, reptiles or cage birds, imported in small-sized containments from a wide variety of geographic origins. The increasing species and origin diversity of these animals may have in the future a strong impact on the risk of introduction of arboviruses in the EU.     

The Application of Molecular Markers in the Study of Diversity in Acarology: a Review

The application of molecular markers to the study of ticks and mites has recently yielded new insights into their population structures and taxonomic relationships. Ticks have been studied at individual, population and species level. Mites are a more diverse group and those that have been studied to the same degree as the ticks include the Tetranychidae (spider mites), Phytoseiidae (predatory mites) and the Eriophyidae. Population variation has also been studied in the important bee parasitic mite Varroa jacobsoni Oudemans. The methods used to study these organisms have much in common. At the individual level these range from general approaches, such as AFLP, RAPD or DALP, to highly specific microsatellite analysis. Although these markers also work at the population and species level, additional analysis of specific nuclear or mitochondrial genes has been conducted either by RFLP or sequencing. Molecular applications have had particular success in facilitating the identification of taxonomically difficult species, understanding population structures and elucidating phylogenetic relationships.     

A review on the impacts of feral cats (Felis silvestris catus) in the Canary Islands: implications for the conservation of its endangered fauna

Feral cats have been directly responsible for the extinction of numerous species on islands worldwide, including endemic species of mammals, birds and reptiles. The diet of feral cats in the main habitats of the Canary Islands, as generally occurred on oceanic islands, is mainly composed of introduced mammals, and native species of birds, reptiles and insects. The impact of feral cat upon the endangered species was assessed by evaluating their relative abundance in the cats’ diet and by considering their current conservation status. A total of 68 different preys were identified at species level in all studies carried out in the Canary Islands (5 mammals, 16 birds, 15 reptiles and 32 invertebrates). From all the species preyed by feral cats in the Canary Islands, only four of them are considered threatened by the IUCN Red List of Threatened Species: one endemic bird Saxicola dacotiae and three endemic giant lizards, Gallotia simonyi, Gallotia intermedia, and Gallotia gomerana. Although some efforts on management control have been carried out, it is necessary to enforce these conservation activities on those areas of Tenerife, La Gomera and El Hierro where giant lizards are still present. Furthermore some local areas where endangered bird species are highly predated should be protected. Nevertheless, it is important to take into account the presence of other introduced species such as rats, mice or rabbits in order to avoid problems derived from the hyperpredation process and mesopredator release effect.     

Microorganisms in the ticks Amblyomma dissimile Koch 1844 and Amblyomma rotundatum Koch 1844 collected from snakes in Brazil

Knowledge about ticks (Acari) and screening of ticks parasitizing various hosts are necessary to understand the epidemiology of tick‐borne pathogens. The objective of this study was to investigate tick infestations on snakes (Reptilia: Squamata: Serpentes) arriving at the serpentarium at the Institute Vital Brazil, Rio de Janeiro. Some of the identified ticks were individually tested for the presence of bacteria of the genera Rickettsia (Rickettsiales: Rickettsiaceae), Borrelia (Spirochaetales: Spirochaetaceae), Coxiella (Legionellales: Coxiellaceae), Bartonella (Rhizobiales: Bartonellaceae), Ehrlichia (Rickettsiales: Anaplasmataceae), Anaplasma (Rickettsiales: Anaplasmataceae), and Apicomplexa protozoa of the genera Babesia (Piroplasmida: Babesiidae) and Hepatozoon (Eucoccidiorida: Hepatozoidae). A total of 115 hard ticks (Ixodida: Ixodidae) were collected from 17 host individuals obtained from four Brazilian states. Two species of tick were identified: Amblyomma dissimile Koch 1844 (four larvae, 16 nymphs, 40 adults), and Amblyomma rotundatum Koch 1844 (12 nymphs, 43 adults). Rickettsia bellii was found in A. rotundatum and A. dissimile ticks and Rickettsia sp. strain Colombianensi, Anaplasma‐like and Hepatozoon sp. in A. dissimile ticks. Among the tested ticks, no DNA of Borrelia, Bartonella, Coxiella or Babesia was found. The present findings extend the geographic range of Rickettsia sp. strain Colombianensi in Brazil and provide novel tick–host associations.     

A review of the ticks (Acari, ixodida) of Brazil, their hosts and geographic distribution - 1. The state of Rio Grande do Sul, southern Brazil

A review of the ticks (Acari, Ixodida) of the State of Rio Grande do Sul, southern Brazil, was completed as a step towards a definitive list (currently indicated as 12) of such species, their hosts and distribution. The ticks: Argas miniatus (poultry), Ixodes loricatus (opossums), Amblyomma aureolatum (dogs), A. calcaratum (anteaters), A. cooperi (capybaras), A. nodosum (anteaters), A. tigrinum (dogs) (Neotropical) and Rhipicephalus sanguineus (dogs) (introduced, cosmopolitan, Afrotropical) were confirmed as present, in addition to the predominant, Boophilus microplus (cattle) (introduced, pan-tropical, Oriental). Of the further 18 species thus far reported in the literature as present in the state, but unavailable for examination: only Ornithodoros brasiliensis (humans and their habitations) (Neotropical), Ixodes affinis (deer) (Nearctic/Neotropical) and I. auritulus (birds) (Nearctic/Neotropical/Afrotropical/ Australasian) are considered likely; 13 species would benefit from corroborative local data but the majority appear unlikely; reports of A. maculatum (Nearctic/Neotropical, but circum-Caribbean) are considered erroneous; the validity of A. fuscum is in doubt. The very recent, first known report of the tropical Anocentor nitens (horses)(Nearctic/Neotropical), but still apparent absence of the tropical A. cajennense (catholic) (Nearctic/Neotropical) and the sub-tropical/temperate Ixodes pararicinus (cattle) (Neotropical) in Rio Grande do Sul are important for considerations on their current biogeographical distribution and its dynamics in South America. The state has relatively long established, introduced ("exotic"), Old World tick species (B. microplus, R. sanguineus) that continue to represent significant pests and disease vectors to their traditional, introduced domestic animal hosts, cattle and urban dogs. There are also indigenous, New World ticks (A. miniatus, O. brasiliensis, A. aureolatum, A. nitens), as both long established and possibly newly locally introduced species in the state, that should be considered as potential and emergent pests and pathogen vectors to humans and their more recently acquired, introduced domestic animal hosts; rural poultry, dogs and horses.     

Invasion of exotic earthworms into ecosystems inhabited by native earthworms

The most conspicuous biological invasions in terrestrial ecosystems have been by exotic plants, insects and vertebrates. Invasions by exotic earthworms, although not as well studied, may be increasing with global commerce in agriculture, waste management and bioremediation. A number of cases has documented where invasive earthworms have caused significant changes in soil profiles, nutrient and organic matter dynamics, other soil organisms or plant communities. Most of these cases are in areas that have been disturbed (e.g., agricultural systems) or were previously devoid of earthworms (e.g., north of Pleistocene glacial margins). It is not clear that such effects are common in ecosystems inhabited by native earthworms, especially where soils are undisturbed. We explore the idea that indigenous earthworm fauna and/or characteristics of their native habitats may resist invasion by exotic earthworms and thereby reduce the impact of exotic species on soil processes. We review data and case studies from temperate and tropical regions to test this idea. Specifically, we address the following questions: Is disturbance a prerequisite to invasion by exotic earthworms? What are the mechanisms by which exotic earthworms may succeed or fail to invade habitats occupied by native earthworms? Potential mechanisms could include (1) intensity of propagule pressure (how frequently and at what densities have exotic species been introduced and has there been adequate time for proliferation?); (2) degree of habitat matching (once introduced, are exotic species faced with unsuitable habitat conditions, unavailable resources, or unsuited feeding strategies?); and (3) degree of biotic resistance (after introduction into an otherwise suitable habitat, are exotic species exposed to biological barriers such as predation or parasitism, “unfamiliar” microflora, or competition by resident native species?). Once established, do exotic species co-exist with native species, or are the natives eventually excluded? Do exotic species impact soil processes differently in the presence or absence of native species? We conclude that (1) exotic earthworms do invade ecosystems inhabited by indigenous earthworms, even in the absence of obvious disturbance; (2) competitive exclusion of native earthworms by exotic earthworms is not easily demonstrated and, in fact, co-existence of native and exotic species appears to be common, even if transient; and (3) resistance to exotic earthworm invasions, if it occurs, may be more a function of physical and chemical characteristics of a habitat than of biological interactions between native and exotic earthworms.