Brown recluses take about 1 year to mature from hatching to adult. As adults they can live 2+ years in a laboratory, but can expect to live on average about 3 months in a natural situation. They are active at temperatures ranging from 40 to over 100°F in the south-central part of the United States, and are absent from both coasts. Related species occur in the extreme southern deserts of the U.S.

This nocturnal spider prefers dark, dry, undisturbed areas such as in basements, attics, sheds, and garages underneath clutter, in boxes and other containers. In a natural habitat they can be found under stones and logs or bark. Like most spiders, the brown recluse is not very selective in what it eats, choosing any prey of suitable size that it can subdue including other spiders and insects. Spiders (including other brown recluses) are a significant part of their diet. However, due to their low metabolism and sedentary nature, brown recluses can survive long periods of time without food and indefinitely without access to water except that found in their prey.  

Recluses are sit-and-wait predators that weave an indistinct web usually over a flat surface which serves as a “trip-wire” alerting them to the presence of nearby prey. They may spend days or even weeks in the same small area, rarely moving more than a meter. While they will scavenge dead insects in the lab, and to a limited extent in the wild, predation of live insects is their preference. Mating occurs can occur from February to October but mainly in June and July. Females lay 1 to 5 egg sacs in a lab setting with up to 90 eggs per sac. On average it takes almost a month for the eggs to hatch. There are 8 stages (instars) and a recluse typically leaves its mother at the 3rd or 4th instar. Molting, or casting of the exoskeleton, is a very stressful time for the spider during which many die. Brown recluses (like most other spiders) don't molt after becoming sexually mature.  

Sources

Hite, J.M., W.J. Gladney, J.L. Lancaster, Jr. & W.H. Whitcomb. 1966. Biology of the brown recluse spider. Arkansas Experiment Station Bulletin 711:3–26.

Cramer, K. L. 2008. Are brown recluse spiders, Loxosceles reclusa (Araneae, Sicariidae) scavengers? The influence of predator satiation, prey size, and prey quality. The Journal of Arachnology 36:140-144

Cramer, K. L. 2015. Activity patterns of a synanthropic population of the brown recluse spider, Loxosceles reclusa (Araneae, Sicariidae) with observations on feeding and mating. Journal of Arachnology 43:67-71.

Cramer, K. L. & L. M. Zagar. 2016. High temperature tolerance of the brown recluse spider (Aranea, Sicariidae): potential for pest control. Journal of Economic Entomology 109:284-287.