Though the best known natural enemies of arachnids are Hymenoptera, Diptera also form an important group of arachnid enemies, attacking 31 spider families in all three suborders of Araneae, as well as members of the Acari, Amblypygi and Scorpiones. Some species of Bombyliidae, Chloropidae, Drosophilidae, Ephydridae, Phoridae and Sarcophagidae are known to attack eggs of several families of arachnids, acting as predators, parasitoids and/or parasites of egg sacs. Alternatively, members of Acroceridae and Tachinidae are internal parasitoids, attacking juvenile and/or adult spiders. One species of Sarcophagidae is reported as a predator of individual Liphistiidae (Mesothelae) spiders. We summarize the available information on all lineages of Diptera known to attack arachnids, including predators, parasites, kleptoparasites and parasitoids. A table including host records pertaining to the aforementioned dipteran families is presented. Particular emphasis is given to Acroceridae, the only lineage of Diptera known to develop exclusively on arachnids, and one of the most significant groups of natural enemies of spiders.

The integration of fossil and extant lineages in evolutionary analyses allows for morphological change to be examined over long periods of time. This study explores how fossil archaeid species compare with extant species in terms of morphological diversity. By adding additional data for fossil species, this study builds upon the total evidence phylogenetic data matrix and the carapace/chelicerae measurements of an earlier analysis. Phylogenetic analyses recovered a monophyletic Archaeidae crown-group, and there is some support for a monophyletic fossil clade. However, analyses did not recover a monophyletic Archaeidae: the fossil Lacunauchenius Wunderlich, 2008 fell outside of the remaining archaeids, although its placement was only weakly supported. Fossil archaeids are morphologically diverse, and compared to extant species, occupy a novel morphological space characterized by shorter features. There has been a shift through time towards the more elongated features of the extant species. Given the unique morphologies of the fossil species, it is likely that fossil archaeids occupied unique niches that are no longer occupied by extant species.

Four new genera of funnel-web spiders of the family Agelenidae C.L. Koch, 1837 from the Baja California Peninsula, Mexico are described and illustrated. Bajacalilena gen. nov. is represented by B. bolzerni sp. nov. and B. clarki sp. nov. Cabolena gen. nov. is represented by C. huiztocatl sp. nov., C. kosatli sp. nov., and C. sotol sp. nov. Callidalena gen. nov. is represented by C. quintin sp. nov. and C. tijuana sp. nov. Lagunella gen. nov. is represented by L. guaycura sp. nov. Additionally, the males of Calilena angelena Chamberlin & Ivie, 1941, Hololena septata Chamberlin & Ivie, 1942, and Rothilena sudcaliforniensis Maya-Morales & Jiménez, 2013 are described for the first time. New records for C. angelena, H. septata, R. cochimi Maya-Morales & Jiménez, 2013, R. pilar Maya-Morales & Jiménez, 2013, and R. sudcaliforniensis are also provided. Molecular analysis of a fragment of cytochrome c oxidase subunit I (COI) provides support for the monophyly of the new genera and facilitated sorting of conspecific males and females. Finally, an identification key to native Nearctic and Neotropical genera of the subfamily Ageleninae is provided.

Since its original description, the theraphosid spider genus Crassicrus Reichling & West, 1996 has not been revised and no new species have been described. While reviewing material deposited in the Mexican National Collection of Arachnids (National Autonomous University of Mexico, Mexico City) and the American Museum of Natural History (New York, USA), we encountered specimens corresponding to four new species of Crassicrus from Mexico. In this revision, we include a redescription of the genus and its type species, C. lamanai Reichling & West, 1996, and describe four new species: C. bidxigui, C. tochtli, C. cocona, and C. yumkimil. Species habitat data are provided, as well as identification keys for males and females. In addition, new keels on the male embolus were identified and are described. In the Theraphosinae, the presence of one retrolateral keel has been reported, but in Crassicrus, there are two or three retrolateral keels, and a new taxonomical nomenclature for these keels is proposed. The genus Crassicrus is recorded from Mexico for the first time, increasing the number of known theraphine genera in the country to 16.

The schizomid family Protoschizomidae, endemic to North America, is represented by two genera and 15 species. While most of the species are distributed in caves in the Sierra Madre Oriental system in Mexico; other species are found in caves in the Sierra Madre Occidental system. Recently, a new species of this family was described from a cave in the Mexican Trans-Volcanic Belt, representing the linking bridge between both Sierras. In the present contribution, we propose a new nomenclature of the pedipalp setae of the protoschizomids. We revise the phylogenetic status of Protoschizomidae using 137 morphological characters (including the proposed pedipalp setae) and 7 outgroup taxa using parsimony criteria. Based on our results, Protoschizomidae was recovered as monophyletic, but the monophyly of Protoschizomus Rowland, 1975 was not recovered because of the inclusion of Agastoschizomus Rowland, 1971 and the fossil Onychothelphynous bonneri Pierce, 1951. Therefore, we transfer the genus Onychothelyphonus Pierce, 1951 and species O. bonneri to this family, but other taxonomical changes were not considered.

The pseudoscorpion genus Haplochernes Beier, 1932, is redescribed and restricted to those species of Chernetidae with only four setae on the cheliceral hand and a pair of moderately long, slender spermathecae. This new definition is shared by only two species: the type species H. boncicus (Karsch, 1881) from Japan and possibly Taiwan and H. wuzhiensis Gao and Zhang sp. nov. from Hainan Island, China. Haplochernes madagascariensis Beier, 1932 from Madagascar and H. hagai Morikawa, 1953 from Japan are treated as new synonyms of H. boncicus.

The family Filistatidae is considered sister to Synspermiata or sister to Hypochilidae. Cytogenetic knowledge of this family could be useful for understanding the mechanism of chromosome evolution that has occurred within the group. In this work, two filistatid species belonging to distinct subfamilies, Kukulcania hibernalis (Hentz, 1842) (Filistatinae) and Misionella mendensis (Mello-Leitão, 1920) (Prithinae), were investigated using standard and differential chromosome staining. Analysis of mitotic and meiotic cells revealed the diploid 2n♂ = 25 for K. hibernalis and 2n♂ = 21 for M. mendensis. Both species exhibited a sex chromosome system of the X₁X₂Y type and metacentric/submetacentric chromosomes. In prophase I cells, the sex chromosomes were in a trivalent configuration with all elements associated without chiasma through their terminal regions. Both species revealed six nucleolar organizer regions on the terminal region of three autosomal pairs. In K. hibernalis, constitutive heterochromatin was located mainly in the terminal regions of autosomes and sex chromosomes while in M. mendensis, the heterochromatin occurred in the pericentromeric region of all chromosomes. Despite the scarcity of cytogenetic information for Filistatidae, the available results show the occurrence of high variability in the diploid number but with the maintenance of the X₁X₂Y sex chromosome system. Additionally, the karyotype differentiation in the species of this family seems to have involved not only the number of autosomes but also specific chromosomal sites, such as the constitutive heterochromatic regions.

Annual crop fields are short-lived and disturbed environments. Therefore, sustainable populations of natural enemies in these fields must be maintained by repeated colonization each season from habitats outside the crop fields. In desert agroecosystems, unmanaged habitats differ greatly in abiotic and biotic conditions from croplands, creating potentially significant barriers to movement of predators. We asked here: to what extent do predators use non-crop habitats as refuges or breeding sites in the desert agroecosystem of the northern Negev, Israel? We investigated the use of natural desert habitat, planted trees (Eucalyptus), and a summer crop (sunflowers) by winter-wheat inhabiting spiders. We collected spiders using pitfall traps and a suction device from wheat fields and adjacent to non-wheat habitats during the wheat season and between seasons. We found that two crop specialist species, Trichoncoides piscator (Simon, 1884) (Linyphiidae) and Thanatus vulgaris Simon, 1870 (Philodromidae), switched to an alternative crop during the inter-wheat season. Habitat generalist species, such as Nomisia sp. (Gnaphosidae), Enoplognatha spp. (Theridiidae) and Alioranus pastoralis (O. Pickard-Cambridge, 1872) (Linyphiidae) used alternative non-crop habitats as refuges and breeding sites to differing degrees in both seasons. While all habitat generalist species used the desert habitat, none used planted trees exclusively as an alternative habitat. We conclude that crop-inhabiting, desert species may be unable to colonize the wheat fields if nearby desert habitat is supplanted by other crops or by tree plantations.

We documented the presence and abundance of spider species (Arachnida: Araneae) on young trees of Swietenia macrophylla, Ceiba pentandra and Cordia dodecandra found in an experimental plantation. Surveys of spider abundance and species identity conducted twice during the growing season indicated marked differences in web-building spider assemblages associated with each tree species. Swietenia exhibited the lowest spider abundance, whereas Cordia and Ceiba had similarly higher abundances. Leucauge venusta (Walckenaer, 1841) was the dominant spider on all tree species, but different spider species were co-dominant on Cordia and Ceiba (Araneus pegnia (Walckenaer, 1841) and Argiope argentata (Fabricius, 1775) respectively), and several spider species were exclusive to each tree species. These results highlight the influence of tree species identity on community structure at higher trophic levels, particularly in the case of web-building spiders inhabiting tropical tree communities.