Twenty-two interactions between males of Loxosceles gaucho Gertsch 1967 were investigated in order to study its intrasexual interactions and level of aggressiveness. Aggression by lunges or bites was observed in just 22.7% of the trials and three behaviors were identified as aggression-attenuating mechanisms: a hug; fleeing, and a postural pattern (POS). Interactions took place in 59.1% of the trials and the pairs interacted using one or two behavioral patterns (vibratory and/or postural). The vibratory pattern (VIB) consisted of foreleg vibration, palpal drumming, and abdominal pulsation and was used by both resident and intruder opponents. The postural pattern (POS) was used exclusively by resident males and it was similar to the behavioral pattern of sexually receptive L. gaucho females; in these cases the intruder male responded using the VIB. In conclusion, the interaction between adult L. gaucho males is usually non-aggressive. The behaviors described in this study possibly promote group-living and help to explain the gregarious populations of recluse spiders. Intra-specific sexual mimicry can occur in these interactions, but this hypothesis requires further investigation.

ABSTRACT. Observations of the developmental biology of Loxosceles gaucho Gertsch, 1967, the brown spider of southeastern Brazil are scarce. The present study reports the method of individualized rearing of 18 populations of L. gaucho, kept in laboratory under varied diet conditions, and characterizes their nympho·imaginal period as well as factors related to their reproduction. Females built the first egg sac about 20 days after copulation and nymphs hatched 40 days after the laying date. Average offspring was 61.3 spiderlings and females usually built three to four successive egg sacs in a period of five to seven months. First nymphs initiated their predatOlY activity between the 5 th and 8 th days after hatching and the majority reached adulthood within six moults (range of five to eight) in approximately 15 to 17 months (male) and 15.5 to 18 months (female). The average sex ratio equa led 1.0:1.7 (male:female). The wide individual variability of this species intermoult intervals is herewith expressed by the "intermoult rate", which was fairly unitorm tor both intra and interpopulations and gives a relevant aspect for a general idea of the life cycles of spiders.

Some brown spider species infest man-made environments and pose a threat to human health. Because habitat architecture affects spider populations, I evaluated the preferences of individuals of Loxosceles gaucho (Gertsch) (Araneae: Sicariidae) for refugia with different angular structures. Four differently angled refugia models (acute-, right-, obtuse-angled and cylindrical) were placed on the litter of a forest fragment and observed each month for 1 year. Females of this species were found to prefer refugia with acute angles. This finding brings new information to our understanding of brown spider infestations in man-made environments: refugia with acute angles are likely to offer more protection for females and their offspring.