Badumna longinqua (L. Koch 1867) is a medium-sized spider native from Australia. Due to its synanthropic habitat, this spider expanded their range distribution, reaching Germany, Japan, New Zealand, Uruguay and USA. We found specimens of this species in different localities from Buenos Aires Province, Argentina. Therefore, we report the first records of B. longinqua to Argentina, and discuss aspects of its distribution.

1. Major floods of riparian and grassland habitats may lead to a shift in the availability of resources (e.g., food, space) that produces cascading effects on the organisms that rely on it. After flooding occurs, particularly in natural grasslands or agricultural fields, massive aggregative spider webs are occasionally observed. However, given it is an infrequent and unpredictable event, it is seldom reported in detail.2. We characterise two instances of massive web aggregations that followed major floods in grasslands and agricultural fields in Argentina and Uruguay in 2015. In the Argentinean event, we compare the composition of spider assemblages on the webs, in grasses below the webs, and in grasses from nearby habitats, with samples taken in the same location but when the fields were not flooded.3. The assemblage of spiders in the massive web aggregations largely consisted of immature Diapontia uruguayensis (Lycosidae). In the grass below the webs, we recorded an impressive density of 1007 specimens m−1 belonging to several spider species, 6–15 times the density of similar samples without aggregated webs, co‐occurring and showing low levels of aggression among them.4. Our observations and review of the literature support the idea massive webs produced by lycosids are a byproduct of an unusually high density of spiders simultaneously attempting to disperse through the air via ballooning and escaping from floods.

Phenotypic plasticity has been defined as the ability of a genotype to produce different phenotypes when exposed to distinct environments throughout its ontogeny. Morphological variability of individuals is an example of this plasticity. Taking into account that several studies have reported a wide morphological variability in Varroa destructor populations, we evaluated if the body size plasticity of the parasite constituted a key factor able to modulate mites survival when they were exposed to a drug bioassays. Drug bioassays against mites were conducted using three different Syzygium aromaticum essential oil concentrations (0.5, 1, and 5 μl/capsule) and controls. After 4 h of exposition, mite mortality was registered. The width (WS) and length (LS) of the dorsal shield were measured in dead mites. General lineal models were carried to determine if V. destructor survival to acaricides was related to the explanatory variables. Data modelling confirmed that WS and LS variables, together with time interaction, were significantly related to V. destructor survival when the parasites were exposed to acaricides. The models proposed demonstrated that for the smaller S. aromaticum essential oil concentration, the larger the parasite body, the greater the probability that it remains alive at the end of the bioassay. Such relationship was inverse for the other two concentrations tested. Possible causes explaining the body size variability in V. destructor individuals were discussed.

RESUMEN. Los hormigueros de varias especies de Acromyrmex presentan sobre el suelo una elevación (túmulo), que posee condiciones micro climáticas estables y ofrece un ambiente atractivo para ácaros oribátidos y otros invertebrados edáficos. Estudiamos los ensambles de oribátidos (Acari: Oribatida), otros ácaros y artrópodos en túmulos de dos especies de Acromyrmex en la Reserva Integral Laguna de Los Padres, Provincia de Buenos Aires. A partir de muestras del túmulo de hormigueros de Acromyrmex lundii y A. ambiguus y del suelo circundante, encontramos 1440 oribátidos pertenecientes a 18 familias, 25 géneros y 34 especies (tres de ellas no habían sido descriptas antes). Los oribátidos fueron el grupo más abundante y su abundancia fue el único parámetro que resultó mayor en los túmulos que en el suelo circundante. En cambio, su riqueza, diversidad y equitatividad no se diferenciaron entre sitios o entre especies de hormiga. La composición de especies de oribátidos varió entre sitios pero las especies más abundantes fueron las mismas en el túmulo y el suelo. Se halló una relación inversa entre la densidad del sustrato (túmulo o suelo) y la densidad de Oribatida. Se sugieren posibles especies mirmecófilas [Palabras clave: hormigas cortadoras, eco-región Pampas]ABSTRACT. Assemblages of oribatid mites in ant nests of Acromyrmex spp. (Hymenoptera, Formicidae): Nests of Acromyrmex spp. exhibit aboveground elevations (tumulus) which maintain a stable microclimate, offering an attractive environment for oribatids and other soil invertebrates. We studied assemblages of Oribatid mites (Acari: Oribatida) in tumuli of two species of Acromyrmex in Integral Reserve Laguna de Los Padres, Buenos Aires province. Samples from nests of Acromyrmex lundii and A. ambiguus, and from their surrounding soil revealed the presence of 1440 oribatids belonging to 18 families, 25 genera and 34 species. Three of the species had not been previously described. Oribatid mites was the most abundant group and were more abundant on tumulus than in the surrounding soil. Conversely, its richness, diversity and evenness did not differ between sites or between ant species. The species composition varied between sites but the most abundant species were the same in tumuli and soil. We found an inverse relationship between density of substrate (tumulus or soil) and density of Oribatida. Potential myrmecophilous species were identified.

Dos nuevos registros de arañas exóticas en Argentina (Arachnida: Araneae)RESUMEN. Dos arañas exóticas se reportan por primera vez en Argentina: Ozyptila praticola (C.L. Koch) (Thomisidae) y Microctenonyx subitaneus (O. Pickard-Cambridge) (Linyphiidae), constituyendo la primera de ellas el primer registro conocido para el hemisferio sur. Los especímenes fueron hallados en hojarasca y bajo corteza de árboles en ambientes