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.

Harvestmen belong to the order Opiliones, and, unlike other arachnids, they are highly polygynandrous, with both males and females mating multiply throughout the breeding season. In this chapter, we review the current information on sexual selection in the group, focusing mostly on intersexual interactions. Particularly, we provide an overview of harvestman mating systems, examine different temporal phases of male-female sexual interactions, and explore cases of sex role reversal. Several traits in harvestmen make them unique in the context of most previous studies of sexual selection. First, they have evolved an intromittent organ independently of other well-studied taxa, such as insects, spiders, and mammals. Second, the lack of long-range perception mechanisms reduces the window of opportunity for males and females to exchange information during the very short period between the first contact and intromission. In some cases, however,

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This paper describes the sexual behavior of Bothriurus buecherli San Martin 1963 and compares it with the rest of the B. prospicuus group. The mating behavior was very similar to other species of the group, but B. buecherli presented some differences in the initial stages, one being a long period of inactivity after the male grasps the female pedipalps. Information presented includes reference to the sexual sting, post-partum copulation, and an analysis of a case of cannibalism by the female.