The spider Latrodectus mirabilis (Holmberg, 1876) is commonly found in cereals crops of central Argentina. We studied its diet composition at the field and capture rate on leaf-cutting ants based on laboratory experiments. This study comprises the first approach that documents the diet of L. mirabilis in wheat and oat fields of central Argentina. We identified 1,004 prey items collected from its webs during the last phenological stages of both cereal crops. The prey composition was variable but the spiders prey mainly on ants (Formicidae, Hymenoptera), who represented more than 86% of the total. Meanwhile, in the capture rate experiences we registered a high proportion of ants captured by spiders at the beginning of experiences, capturing the half of the ants from total in the first four hours. Summarizing, we reported a polyphagous diet of this spider species in wheat and oat fields. Ants were the most important prey item of this spider, as found in other Latrodectus spiders around the world.

La araña Latrodectus mirabilis (Holmberg, 1876) se encuentra comúnmente en cultivos de cereales del centro de Argentina. Se estudió la composición de la dieta a campo y la tasa de captura sobre hormigas cortadoras negras a laboratorio. Este estudio documenta el primer registro de la dieta de L. mirabilis en cultivos de trigo y avena del centro de Argentina. Se identificaron 1004 ítem presa colectados de las telas de L. mirabilis en las últimas etapas fenológicas de ambos cultivos. La composición de presas fue variable, pero las arañas se alimentaron principalmente de hormigas (Formicidae, Hymenoptera), las cuales representaban más del 86% del total de las presas capturadas. A su vez, en las experiencias de tasa de captura, registramos una alta tasa de captura de hormigas al inicio de las mismas, capturando la mitad de las hormigas en las primeras cuatro horas. En resumen, reportamos una dieta polífaga en esta especie de araña en los cultivos de trigo y avena. El ítem presa más importante fueron las hormigas, resultados similares a los encontrados en otras especies del género Latrodectus.

This study provides the first accurate records of Latrodectus geometricus C. L. Koch, 1841 for Uruguay and extends the known distribution of this species to the Southeastern region of South America. Data and figures of the genitalic morphology for the recognition of the species and natural history in this country are indicated. In Uruguay L. geometricus was mainly restricted to urban areas at the west of this country and it is associated with locations with high human activity.

Este estudio reporta los primeros registros precisos de Latrodectus geometricus C. L. Koch, 1841 en Uruguay y extiende la distribución conocida de esta especie para la región sureste de Sudamérica. Datos y figuras de las estructuras genitales para el reconocimiento de la especie e historia natural en este país son indicados. En Uruguay L. geometricus se encuentra principalmente restringida a áreas urbanas del oeste de este país y asociada a sitios con elevada actividad humana.

O macho de Latonigena auricomis Simon, 1893 é descrito pela primeira vez e a fêmea é redescrita. Novos registros são fornecidos pra Argentina, Brasil e Uruguai. São apresentadas notas sobre a história natural e um modelo de distribuição potencial da espécie na Região Neotropical.

The male of Latonigena auricomis Simon, 1893 is described for the first time and the female is redescribed. New records are provided for Argentina, Brazil and Uruguay. Notes on the natural history and a potential distribution model of the species are presented in the Neotropical Region.

Phoneutria bahiensis Simó & Brescovit, 2001 is a large ctenid spider inhabiting the states of Bahia and Espírito Santo, Brazil. Considering that it is probably endemic, this species was included in the Brazilian red book of threatened species. Here, we predict the distribution range of P. bahiensis using 19 bioclimatic variables in the model design. The most septentrional record for this spider was indicated for northern Bahia. The model predicts that the distribution range covers the Atlantic Forest from the state of Paraíba to Rio de Janeiro, with the best suitable area in the Atlantic Forest of the state of Bahia. The bioclimatic variable with the best contribution to the model was precipitation in the driest quarter. Based on collected data, the species inhabits Ombrophilous Forests and Restinga vegetation, two ecosystems of the Atlantic Forest biome. In the best-predicted area of distribution, eleven Conservation Units were included. This information could be considered for future conservation plans of this species.

Holocnemus pluchei y Spermophora senoculata fueron halladas en construcciones humanas en cuatro localidades de Uruguay y una de Argentina. Estos son los primeros registros para Sudamérica de estas dos especies sinantrópicas.