Ecology and behaviour of the ‘road tarantulas’Eupalaestrus weijenberghiandAcanthoscurria suina(Araneae, Theraphosidae) from Uruguay

Abstract

Spatial distribution, burrow morphology, phenology, defensive displays and predation of two theraphosid spiders living in meadows were studied in Uruguay. Exhaustive field studies complemented with laboratory observations were carried out. Eupalaestrus weijenberghi occurred throughout the country while Acanthoscurria suina occurred only in the southern half. Both species seemed to be the most abundant theraphosid spiders in Uruguay as they live in the dominant landscape of the country. Burrows from both species showed a similar morphological pattern but a terminal narrow tube was found only in E. weijenberghi. We observed that A. suina always co-occurred with E. weijenberghi but this species frequently occurred in the absence of the former. When cooccurring A. suina showed an aggregated distribution while E. weijenberghi was randomly distributed. A restricted reproductive period was found for both species, mainly between March and April, evidenced by the massive presence of walking adult males and then confirmed by pit-fall traps. Moulting, oviposition and longevity were also studied. Conspicuous species-specific defensive behaviours were displayed by the tarantulas in all cases, when collected. These tarantulas showed spatial co-occurrence and temporal coexistence with the beetle Diloboderus abderus, an important pest of grasslands. Tarantula predation on adult beetles was confirmed, these spiders being one of the few beetle predators. Their maximal efficiency in beetle predation could reach 65 000 prey captured per hectare by month. These polyphagous tarantulas seem to be potential agents for the biological control of beetle pests.

The stridulatory setae of Acanthoscurria suina (Araneae, Theraphosidae) and their possible role in sexual communication: an experimental approach

“…We excavated a burrow in each cage similar to the natural one (PÉREZ-MILES et al, 2005) against the glass wall, allowing the observation inside the burrow. Each female was placed at least 24 h before the trial.…”

“…Males were collected during a short period of time (ends of February -first days of March 2004), immediately they reached adulthood at the field (PÉREZ-MILES et al, 2005). Females were maintained in the laboratory at least from one year before, allowing us to know their previous reproductive status (usually, they molt one time per year).…”

On the Brazilian Amazonian species of Acanthoscurria (Araneae: Theraphosidae)

“…A female of A. insubtilis was observed, during the night, digging a burrow with her palps and legs I-II (Fig. 41), as in some other Theraphosidae (PÉREZ-MILES et al 2005, INDICATTI et al 2008) and the majority of other mygalomorphs (COYLE 1971, LUCAS et al 2005. Males were collected walking in the forest litter.…”

“…The species is mainly nocturnal but in reproductive periods males can be found during the day, walking in the forest litter and crossing roads as other species of the genus (PÉREZ-MILES et al 2005, GONZALEZ-FILHO et al 2012. Females and juveniles dwell in tubular burrows, located under rocks, fallen trunks, inside living trees and in ravines and on the ground level.…”

“…These spiders are aggressive, bite and easily throw urticating setae when disturbed. They can also display defensive behavior by raising the anterior legs, palps and opening the chelicerae, thus exposing the red ventral setae; at this moment the spiders open the fangs, releasing poison droplets in some cases, and make false attacks (mainly males), like A. suina (PÉREZ-MILES et al 2005) and A. gomesiana Mello-Leitão, 1923(GONZALEZ-FILHO et al 2012. Vol, 2000 Figs 22-28, 60 Acanthoscurria simoensi Vol, 2000: 8, pl Diagnosis.…”