Terrestrial Gastropod Species Research Articles

Ulitníky pseudokrasovej tiesňavy Parkaň v pohorí Bachureň na východnom Slovensku [Gastropods of the Parkaň pseudokarst gorge in the Bachureň Mountains in Eastern Slovakia

A pseudokarst gorge with the local name „Parkaň“ is located near the village of Renčišov in the Bachureň Mountains. This area was surveyed in 2023. In total, we recorded 52 species of terrestrial gastropods. These were predominantly forest species (38; 73%), euryvalent species were less represented (13; 25%), and one open country species was also found (1; 2%). The local microtopographic diversity (moist rubble, rock walls covered with moss, dead wood) with historic habitat continuity support the high species diversity of the gastropod fauna. The results highlight the conservation importance of the area and the presence of sensitive species such as Argna bielzi, Macrogastra tumida, Pseudalinda stabilis and Bulgarica cana, indicating the well-preserved state of the habitat. This area represents a local diversity hotspot surrounded by mostly disturbed production forest monocultures. The discovery of one, slightly damaged shell of the species Helicigona lapicida is interesting. Since we could not find live individuals, we do not consider this finding a reason to include the species in the malacofauna of Slovakia.

Shells, teeth and DNA: land snails from an urban forest in Rio de Janeiro, SE Brazil

ABSTRACT This study aims to explore the diversity of land snails in a forested area of the second largest Brazilian city (Rio de Janeiro), through the study of basic morphology (ie shell, operculum, jaw and radula) and the barcode of COI sequences. The conservation unit ‘Parque Natural Municipal da Cidade’ (PNM da Cidade) is a fragment of the Atlantic Forest biome. During 12 fieldwork visits, 17 species of terrestrial gastropods were found in PNM da Cidade, of which six are synanthropic, exotic/cryptogenic, and occurred in single or few sampling stations, whereas the 11 native species varied in their range. PNM da Cidade houses a large population of the native species Thaumastus cf. taunaisii (Férussac, 1822), always found close to water sources, but it demands conservation concern. The sampling of live specimens allowed the study of operculum, jaw or radula from five selected species, and the generation of 20 COI sequences from 10 species, elucidating taxonomic aspects. The gastropod fauna at PNM da Cidade is indicative of moderately preserved habitats, despite some anthropic pressure. Future geography-based studies of land snails could add DNA sequences in order to enable the discovery or elucidation of cryptic complexes of species.

Surveillance of land molluscs infected by Angiostrongylus cantonensis (Nematoda) reveals risk areas for zoonotic eosinophilic meningitis in the State of Rio de Janeiro, Brazil.

The nematode Angiostrongylus cantonensis, which is endemic to Southeast Asia and adjacent Pacific Islands, has already been recorded in more than 30 countries, including Brazil and other South American nations. It is one of the principal etiological agents of the zoonosis Eosinophilic Meningitis (EoM), which has a number of different species of terrestrial gastropods that act as its intermediate hosts. The present study investigated the occurrence of the larvae of this nematode in specimens of terrestrial molluscs collected in half of the municipalities of the Brazilian State of Rio de Janeiro. The study is based on the surveillance of this nematode in the Brazilian State of Rio de Janeiro, where terrestrial snails and slugs were collected in more than half of the state's municipalities (46 in all), and examined for parasitological infections. The nematode larvae retrieved from these specimens were identified based on their morphology and cytochrome oxidase I (COI) mitochondrial DNA sequences. Angiostrongylid larvae were found in 230 (8.8%) of the 2,600 terrestrial molluscs examined, collected from 26 municipalities. Overall, 14 terrestrial gastropod species were identified, including both native and exotic taxa, and six were found to be infected naturally by A. cantonensis. The natural infection rates by Angiostrongylus in the different terrestrial molluscs species were 12.5% in Angustipes erinaceus, 9.7% in Achatina fulica, 6.8% in Bradybaena similaris, 6.3% in Sarasinula linguaeformis, 3.9% in Leptinaria unilamellata, and 4.6% in Subulina octona. A. fulica was the most frequent and extensively distributed species, with infected snails being found in 22 municipalities. The data from this first comprehensive survey of A. cantonensis in Rio de Janeiro highlights the potential epidemiological risk of human infection in this state. Mapping the spread of infected molluscs will also provide essential information for the evaluation of the risk of human infection, and should help local health authorities to provide a faster and more accurate diagnosis whenever neuroangiostrongyliasis is suspected.

Gastropods on the green roof of a high-rise building in a large European city

Understanding the distribution and diversity of terrestrial snails on green roofs (GR) can facilitate insights into the ecological functioning of these urban habitats. While green roofs have been shown to provide suitable habitat for mobile species such as birds and insects, there needs to be more research concerning the colonisation and persistence of less mobile animal groups, including terrestrial gastropods. The present study investigates the species richness of terrestrial gastropods on green roofs of high-rise buildings in Bratislava, Slovakia. The study examined four distinct types of green roofs: The green roofs were classified according to their management intensity, resulting in four categories: extensive, semi-intensive GR-A, semi-intensive GR-B, and intensive. The categories differed in terms of vegetation, substrate depth, irrigation, and sun exposure. The survey employed a variety of methods, including pitfall trapping, vegetation sweeping, soil sampling, and microhabitat investigations. The survey yielded evidence of 11 species of terrestrial gastropods (six snails and five slugs) inhabiting three GR types. The semi-intensive GR-A, which is characterised by dense vegetation and minimal management, supported all 11 species. No gastropods were observed on the extensive GR with shallow substrate and Sedum sp. vegetation. The presence of native and non-native species, including the non-native slug Ambigolimax valentianus, indicates that terrestrial gastropods can colonise GR. These findings emphasise the potential of GR to support urban biodiversity and highlight the need for further research on less mobile species in these habitats.

The biocontrol nematode Phasmarhabditis hermaphrodita infects and increases mortality of Monadenia fidelis, a non-target terrestrial gastropod species endemic to the Pacific Northwest of North America, in laboratory conditions.

Inundative biological control (biocontrol) efforts in pest management lead to the mass distribution of commercialized biocontrol agents. Many 'biocontrol gone awry' incidents have resulted in disastrous biodiversity impacts, leading to increased scrutiny of biocontrol efforts. The nematode Phasmarhabditis hermaphrodita is sold as a biocontrol agent on three continents and targets pest gastropods such as Deroceras reticulatum, the Grey Field Slug; P. hermaphrodita is not presently approved for use in the United States. Investigations into the potential for P. hermaphrodita to infect non-target gastropod species of conservation relevance, however, are limited. We examined the effects of three strains of P. hermaphrodita on mortality in Monadenia fidelis, the Pacific Sideband, a snail species endemic to the Pacific Northwest of North America, in laboratory conditions. Across a 71-day laboratory infectivity assay, snails exposed to each of the three nematode strains, each analyzed at two doses, experienced a mean 50% mortality by days 20-42. All nematode-treated snails were dead by the end of the study. By contrast, 30/30 water-control snails experienced no mortality. Nematodes killed smaller, juvenile-stage snails significantly faster than those in larger and more developmentally advanced hosts. Our results provide direct evidence that the biocontrol nematode P. hermaphrodita infects and kills M. fidelis, a non-target gastropod species endemic to the Pacific Northwest, in laboratory conditions. This study suggests that introduction of P. hermaphrodita to new ecosystems might negatively impact endemic gastropod biodiversity and advocates for further investigation of non-target effects, including in conditions closer to the natural environments of non-target species.

Měkkýši přírodních památek V Krátkých a Lom Rasová v CHKO Bílé Karpaty [Molluscs of the V Krátkých and Lom Rasová Nature Monuments in the White Carpathians PLA

The V Krátkých Nature Monument (NM) comprises of landscape mosaic of meadows, groves, spring fen and wetland while the Lom Rasová NM is a former sandstone quarry with open and forested areas. Both are situated near Vápenice village in the White Carpathians. In total, 44 species (40 terrestrial gastropods, 3 aquatic snails and 1 bivalve) were found in V Krátkých NM. Three species are listed in the Red List of Threatened Species: Daudebardia brevipes (VU), Lehmannia carpatica (NT) and Bythinella austriaca (NT). Most diversity consists of forest species, followed by eurytopic and hygrophilous species. The spring fen is the most species-rich habitat, as hygrophilous, eurytopic and forest species are present. To retain the favourable conservation status, extensive kettle grazing or mowing of the fen and meadows is suggested while the groves should remain in a non-intervention regime with possible subtle intrusion of broadleaved trees. In the Lom Rasová NM, 18 terrestrial gastropod species were recorded (aquatic malacofauna was not surveyed). All species are common and widespread, and their composition is a mixture of predominantly forest, euryvalent and open-country taxa. To support gastropod diversity, the broadleaved groves should remain in a non-intervention regime, while deciduous trees should be replaced with broadleaved species and overall habitat diversity should be supported.

Litter-dwelling terrestrial molluscs of Nepisiguit Protected Natural Area and Mount Carleton Provincial Park, north-central New Brunswick

No comprehensive study of the terrestrial gastropod fauna of northern New Brunswick has previously been undertaken. Most terrestrial gastropod molluscs are tiny and generally live unnoticed under debris, in leaf litter, and among other dead and living vegetation. Sifting and sorting collected samples of leaf litter are effective in sampling snails. In June–July 2015 and August 2016, 43 samples of forest leaf litter were collected in Nepisiguit Protected Natural Area and Mount Carleton Provincial Park. These samples yielded 22 species of terrestrial gastropods. Seven species are reported from New Brunswick for the first time.

Species richness patterns and community structure of land snail communities along an urban-rural gradient in river floodplains

Urbanisation is widely considered as having a large impact on most native species. However, the species response to urbanisation varies among taxonomic groups, and its generalisation might lead to contradictory or incorrect management decisions in urban planning. Land snails, as an understudied group in this sense, are good subjects to study the impact of urbanisation due to their low dispersal capabilities and mobility. The study aimed to determine how land snail diversity patterns and community structure are influenced by urbanisation through an urban-to-rural gradient. A total of 59 terrestrial gastropod species and more than 4600 individuals were recorded at 24 alluvial sites distributed along an urban-to-rural gradient in three Slovak cities (Bratislava, Zvolen and Prešov). Most species belonged to euryecious, hygrophilous and forest specialist ecological groups; seven species were non-native to Slovakia. The results clearly highlight the negative effect of densely built areas on land snail community structure, since the proportion of indigenous and specialist species decreased progressively towards urban sites. The highest mean number of species was found in suburban zones and the lowest in urban zones, suggesting that most species favour intermediate levels of urbanisation. Some species (e.g. Arion vulgaris) were evenly distributed along the urbanisation gradient, supporting the importance of river floodplains as bio-corridors for the dispersal of gastropods.

Biodiversity dynamics of terrestrial gastropods in the tropical montane rainforests of Nuwara Eliya, Sri Lanka

Sri Lanka is home to 253 terrestrial gastropod species, most of which are endemic. However, limited research has explored the diversity, distribution, and influencing variables of these gastropods. This study sampled gastropods in tropical montane rainforests by establishing 10-50 1m2 sampling plots across 60 randomly selected sites. Among the 46 recorded species, 79% were native, and 17% were exotic. Representative species of the five endemic genera to the island and two endemic semi-slug species were recorded from these forests. Native gastropod species were primarily found in forest interiors, while exotic species inhabited forest buffer regions. The distribution of most native species is influenced by elevation, air temperature, relative humidity, rainfall, and soil pH, while elevation and rainfall play a significant role in the distribution of most exotics. Exotics display broader environmental tolerance compared to natives, enabling exotics to invade the forests. The restricted habitat of many native species within deep canopy forests makes them highly vulnerable to habitat change, whereas exotics thrive under altered conditions.

Molecular phylogeny of the Orthalicoidea land snails: Further support and surprises.

The superfamily Orthalicoidea comprises approximately 2,000 species of terrestrial gastropods, mostly concentrated in the Neotropics but also present in southern Africa and Oceania. We provide a multi-marker molecular phylogeny of this superfamily, reassessing its family- and genus-level classification. We exclude two families from the group, Odontostomidae and Vidaliellidae, transferring them to Rhytidoidea based on their phylogenetic relationships as recovered herein. Two new families are recognized herein as members of Orthalicoidea, Tomogeridae and Cyclodontinidae fam. nov. The family Megaspiridae and the subfamily Prestonellinae are paraphyletic but are retained herein for taxonomic stability. The subfamily Placostylinae is synonymized with Bothriembryontinae. The new genera Alterorhinus gen. nov. and Sanniostracus gen. nov. containing some Brazilian species are described here to better reflect the phylogeny. The fossil record and paleobiogeographic history of the group is explored under the new phylogenetic framework.

Data on New Intermediate and Accidental Hosts Naturally Infected with Angiostrongylus cantonensis in La Gomera and Gran Canaria (Canary Islands, Spain).

Angiostrongylus cantonensis is a metastrongyloid nematode and the etiologic agent of angiostrongyliasis, a disease characterized by eosinophilic meningitis. This emerging zoonotic parasite has undergone great expansion, including in some regions of Europe and America. In the Canary Islands, the parasite was first discovered parasitizing Rattus rattus on the island of Tenerife in 2010. To date, the distribution of this parasite in the Canary Islands has been restricted to the northern zone and the main cities of Tenerife. Using molecular tools for the sentinel species present in the Canary Islands, this study confirmed the presence of the nematode on two other islands in the Canary Archipelago: La Gomera and Gran Canaria. Furthermore, this emerging parasite was detected, besides in the common definitive host R. rattus, in wild Mus musculus and Felis catus and in four terrestrial gastropod species, Limacus flavus, Milax gagates, Insulivitrina emmersoni, and Insulivitrina oromii, two of them endemic to La Gomera, for the first time, increasing the number of non-definitive host species. This study reinforces the expansion character of A. cantonensis and highlights the importance of knowledge about sentinel species for identifying new transmission locations that help prevent and control the transmission of the parasite and, thus, prevent public health problems.

Reconstructed Malacothermometer July Paleotemperatures from the Last Nine Glacials over the South-Eastern Carpathian Basin (Serbia)

In this study, the compiled malacological record of the two most important loess–palaeosol sequences (LPS) in Serbia was used to reconstruct the Malacothermometer July Paleotemperature (MTJP) of the last nine glacials. The sieved loess samples yielded shells of 11 terrestrial gastropod species that were used to estimate the MTJP. Veliki Surduk (covering the last three glacial cycles) and Stari Slankamen (covering the last fourth to ninth glacial cycle) LPSs previously lacked the malacological investigations. After the sieving, a total of 66,871 shells were found, from which 48,459 shells were used for the estimation of the MTJP. Through the studied period, the reconstructed MTJP was ranging from 14.4 °C to 21.5 °C. The lowest temperature was recorded during the formation of the loess unit L5, equivalent to the Marine Isotope Stage (MIS) 12. The second-coldest summers were occurring during the MIS 16 glacial. Although the warmest glacial was L8 (MIS 20) according to MTJP, these July temperatures might be overestimated due to only two samples from the poorly preserved L8 unit. The malacological material derived from the loess units at Veliki Surduk and Stari Slankamen LPSs showed great potential for July temperature reconstruction, as the comparison with other regional records showed similar climate changes. Further work is necessary to validate the age scale of the oldest samples, and a higher resolution sampling could lead to more detailed July temperature fluctuations, as was shown for the youngest glacial in this study. Likewise, estimating the July temperature using different proxies (e.g., pollen) from the same LPSs could be used to confirm the observed climate trends.

Invasion Potential of Ornamental Terrestrial Gastropods in Europe Based on Climate Matching

Invasive species are one of the main causes of biodiversity loss worldwide. Pet trade is a well-known pathway for the introduction of non-native species. Prevention is the most effective, least time-consuming, and least financially demanding way to protect biodiversity against the spreading of invasive species. The main part of prevention is the early detection of a potentially high-risk species, as well as the successful implementation of prevention strategies in legislation and practice. This study summarizes the pre-introduction screening of pet-traded terrestrial gastropod species and their potential occurrence in the EU territory. Based on the list of species traded in the Czech Republic, one of the most important global hubs of the pet trade, 51 species (49 snails and 2 slugs) were analysed. Due to a lack of certain native occurrence data, only 29 species (28 snails and 1 slug) from 10 families were modelled using MaxEnt software. Twenty species from seven families have potential occurrence in the EU territory. Based on MaxEnt modelling, we considered the following species to be high-risk candidates for the EU: Anguispira alternata, A. strongylodes, Laevicaulis alte, Megalobulismus oblongus, Rumina decollata, and R. saharica. Based on this estimation, we present considerations with which to further improve the risk assessment and recommend continuous monitoring of the pet trade market.

Land molluscs of Sucre State, Continental Northeast of Venezuela, Southeast Caribbean. II: Three (3) new species additions to the regional inventory

Introduction: Since of the year 2014, the “AM Project” (Brazil) has been carrying out taxonomic, bioecological and conservationist research on "non-marine molluscs" present in the environment of the Caribbean continental territory of the Sucre State and adjacent areas, Northeast region of Venezuela , with special emphasis on its terrestrial and arboreal forest species (Agudo-Padrón 2021), a geographic region historically little studied in this aspect of its natural history, involving today a general preliminary total of 67 verified forms/ species (44 land/ terrestrial and 23 limnic/ freshwater), included in 49 genera and 28 families. Objective: Substantial update of this knowledge, with the incorporation of new species to the regional inventory. Methodology: Updated review of cryptic regional malacological bibliography and taxonomic examination & determination of specimens (vouchers) deposited in malacological collection of scientific museum. Results and conclusions: Incorporation of three (3) land/ terrestrial gastropod (forest snail) species into the previously established regional inventory, taxonomically grouped all into 1 genera and 1 family, bringing to 47 its your number of regionally land known forms.

Morphological and Molecular Characterization of the Invasive Pestiferous Land Snail Macrochlamys indica Godwin-Austen, 1883 (Gastropoda: Ariophantidae) from Saudi Arabia

Many terrestrial gastropod species have been dispersed as a result of anthropogenic activities and have adapted to new habitats where they are considered as alien or invasive species. Several synanthropic gastropods are invasive in urban and agricultural environments worldwide. In Saudi Arabia, increased human activities have accelerated the introduction of terrestrial gastropod species, increasing the need to study its gastropod fauna. Our preliminary survey disclosed the presence of ariophantid snails in a number of agricultural nurseries. Based on morphological features of shell, body, and reproductive system, we report the first record of Macrochlamys indica from Saudi Arabia. The phylogenetic analysis obtained from DNA sequences of the mitochondrial COI and 16S regions confirmed the identity of M. indica. One third of the investigated nurseries were infested with this snail, however, we did not find any specimens of M. indica in natural habitats or open agricultural fields. The snail-infested nurseries were distributed all over Saudi Arabia. The occurrence of one haplotype of partial mitochondrial COI sequence from these nurseries suggests that the introduction of M. indica is likely very recent. Based on the obtained results, it is recommended that control measurements must be implemented in order to eradicate or at least restrict the dissemination of M. indica from nurseries to natural habitats or agricultural fields.

The Land Snails and Slugs of Tennessee, USA: Taxonomic Composition, Distribution, and an Evaluation of State-Wide Spatial and Taxonomic Survey Biases

The increased availability of publicly available, digitally accessioned biodiversity data and scientific literature presents the opportunity to reassess geographical associations of understudied taxonomic groups. Using these resources, in addition to occurrence data managed by the National Park Service at the Great Smoky Mountains National Park and private collections, we have assembled an updated taxonomic checklist and robust geographic dataset of all records of terrestrial gastropods (land snails and slugs) within the state of Tennessee. Additionally, we quantified spatial and taxonomic biases in survey coverage and overall survey quality for terrestrial gastropods at two spatial resolutions: ecoregion and county. Our state checklist includes 301 species of terrestrial gastropods that have at least one occurrence record, which increases the number of species by 40 from previous assessments of terrestrial gastropod biodiversity in Tennessee. Spatial analyses revealed < 33% of ecoregions and < 18% of counties to be sufficiently sampled for any terrestrial gastropod group as inferred by accumulation curves and the ratio between number of records to number of genera within each spatial unit. Significant biases in survey coverage in the state were revealed at both spatial scales, and a disproportionate number of occurrence records were found in the eastern portion of the state near urban centers, universities, and the Great Smoky Mountains National Park. Taxonomic diversity estimates were similarly biased. Moreover, larger snails comprise the vast majority of occurrence records compared to snails less than 5 mm in shell diameter and slugs. From a conservation perspective, the addition of many newly reported species requires updating status assessments, and the spatial and taxonomic bias reported here should act as an incentive for future targeted gastropod survey effort, particularly in western Tennessee.

Phylogenetic Position of the Genus Ridleyconcha (Gastropoda, Stylommatophora)

The Fernando de Noronha Archipelago off NE Brazil harbors a few unique terrestrial gastropod species. One of them, the monotypic genus Ridleyconcha Christensen, 2020, presents such an idiosyncratic shell morphology that, in the 130 years since its description, it has been variously allocated in unrelated families: Streptaxidae, Endodontidae, Charopidae, Camaenidae, and Scolodontidae. Herein, R. quinquelirata is included into a molecular phylogenetic framework of stylommatophoran land snails to clarify its taxonomic position. The analysis supports the latest morphological revision classifying Ridleyconcha in Scolodontidae. Considering the present sampling, Ridleyconcha appears to be the sister taxa of Entodina Ancey, 1887.

Radiocarbon age offsets, ontogenetic effects, and potential old carbon contributions from soil organic matter for pre-bomb and modern detritivorous gastropods from central Texas, USA

Carbon isotopes of terrestrial gastropod yield insights on age and paleoenvironments for many depositional settings, but questions remain on the carbon source for gastropod carbonate and the climatic significance. This study documented for four terrestrial gastropod species ( Rabdotus dealbatus, A. alternata, V. indentata, and Rumina decollata) from central Texas 14 C age offsets between shell‑carbonate and corresponding atmosphere values that lived on carbonate- and kerogen-rich Cretaceous bedrock in the 20th and 21st centuries. Also, the ontogenetic variations in 14 C content were assessed to better understand carbon cycling between gastropods and the associated reservoirs. The carbon sources were partitioned based on 13 C isotopic values to evaluate the possible causes for age anomalies using initially a three-component model that includes contributions from atmosphere, vegetation, and limestone pools, with a new added fourth component, for soil organic carbon. The average ( n = 4) of the outer and inner shell samples yielded the respective 14 C ages of 550 ± 325 and 1520 ± 525 yr B.P. The apparent linearized 14 C distance-age anomaly for an individual gastropod whorl is 4–26 mm/yr calculate from shell 14 C ages on apex and aperture material. The smallest gastropod dated, a single V. indentata test (3.9 mg) yielded the oldest 14 C age of 2340 yr B.P. The four-component model for the oldest 14 C ages indicates that 50–85% of shell carbon may be from ingestion, with a smaller pool from respiration. Up to 30% of the organic carbon in gastropod shell may be derived from soil organic carbon. Terrestrial gastropods that yield anomalously old 14 C ages of >500 years may be detritivores and live in soils with sources of labile old carbon either inherited from the bedrock and/or the older pool of soil organic matter common in well-developed calcium-rich soils. • Modern and prebomb terrestrial gastropods from Texas gave 14 C ages 300–2400 yr old. • Gastropod shells show ontogenetic effect with older ages at apex by 100–1700 yr. • Identify new old carbon source for snails from kerogen-rich soil organic matter (SOM) • Develop new four component model (air, rock, SOM and plants) to explain old 14 C ages • Up to 30% of carbon in gastropod shell may be derived from SOM.

Phasmarhabditis quinamensis sp. n. (Nematoda: Rhabditidae) from tropical terrestrial gastropods in southern Vietnam

Summary Phasmarhabditis quinamensis sp. n. was recovered from several tropical terrestrial gastropod species collected in Cat Tien National Park in southern Vietnam with the snail, Sesara sp., designated as the type host. Phasmarhabditis quinamensis sp. n. is recognised by males and females with a lip region set off by the circle of six triangular low probolae, three bilobed, separated lips, stoma nearly as wide as long, the first genital papilla in males not incorporated into the bursa, the ensheathed dauer juveniles more than 1 mm long and with two circles of papillae at the head end and prominent amphidial apertures, a long filamentous tail and, when exsheathed, with a short, conical tail ending with two tiny spikes. The head structure of P. quinamensis sp. n. differentiates it from all nominal species of Phasmarhabditis. Phasmarhabditis quinamensis sp. n. is the second species of the genus found in Cat Tien National Park. The sympatric species P. meridionalis was also found during the present study. Phylogenetically, both species belong to different lineages within Phasmarhabditis. The molecular analysis based on partial sequences of LSU rDNA, and ITS rDNA regions showed P. kenyaensis to be the closest species to P. quinamensis sp. n.

Preliminary Study on Survey and Population Dynamic of the Terrestrial Snail Monacha obstructa (Pfeiffer) (Hygromiidae, Mollusca) at Crop Fields in Fayoum Governorate, Egypt.

&lt;b&gt;Background and Objective:&lt;/b&gt; &lt;i&gt;Monacha obstructa&lt;/i&gt; has a serious harmful impact as agricultural pest infested field crops, fruits, vegetables and ornamental plants nurseries in multiple Egyptian governorates. The objective of this research was estimating the population dynamic of the terrestrial gastropod species &lt;i&gt;Monacha obstructa&lt;/i&gt; (Pfeiffer) (Hygromiidae) on two economic crop fields and its correlation with temperature degree and relative humidity, the level of infestation on other economic crops had been estimated as well. &lt;b&gt;Materials and Methods:&lt;/b&gt; This study was conducted in three sites in Fayoum governorate, 1) Forkous village at Tamiya District, 2) Dar Ramadsite including the Experimental farm and research station of the Faculty of Agriculture, Fayoum University, Fayoum District and 3) Feedimeen village at Sannoris District. The distribution and population dynamics of &lt;i&gt;Monacha obstructa&lt;/i&gt; were assessed as one of dominant species on two field crops Egyptian clover &lt;i&gt;Trifolium alexandrinum &lt;/i&gt;L. and wheat &lt;i&gt;Triticum aestivum&lt;/i&gt; L. at Forkous village, Tamiya District and Dar Ramad site, Fayoum District, during two successive seasons 2016/2017 and 2017/2018. &lt;b&gt;Results:&lt;/b&gt; Majority of the examined crops in the sites were found with heavy infestation of this species, while the two species &lt;i&gt;Cochlicella acuta&lt;/i&gt; (Müller) (Geomitridae) and &lt;i&gt;Massylaea vermiculata &lt;/i&gt;(Müller) (Helicidae) recorded in December, 2017 and in January, 2018, respectively, on mango trees in Feedimeen at Sannoris district for only one time. High density of &lt;i&gt;M. obstructa&lt;/i&gt; recorded on Egyptian clover more than wheat at Forkous village and Dar Ramad site for the both seasons in this study. &lt;b&gt;Conclusion:&lt;/b&gt; Results concluded that &lt;i&gt;Monacha obstructa&lt;/i&gt; has a serious harmful impact as agricultural pest infested field crops, fruits, vegetables and ornamental plants nurseries in Forkous village and Dar Ramad site, respectively.