During the winter of 2014–15 in southern California, attempts were made to accelerate immature brown recluse spiders, Loxosceles reclusa Gertsch & Mulaik, 1940, to maturity for a pest control experiment in early spring. Despite food offerings, spiders stopped molting after October although they were maintained at 25° C and had swollen, well-nourished abdomens. It was surmised that decreased filtered daylight from a paper-covered window might be suppressing molting. Feeding was halted in January 2015; 88 spiderlings were checked weekly for molts. Molting resumed during late March 2015 and continued through May 2015 despite no feedings. To more thoroughly elucidate photoperiod effects on molting, during the week of the September 2015 equinox, three cohorts of 10 immatures of both brown and Chilean recluses, L. laeta (Nicolet, 1849), were exposed to three light regimes: 14:10 L:D, natural, 10:14 L:D. Through November 2015 to late March 2016 for brown recluses, there was no molting in the 10:14 regime, 3 of 10 spiders molted in the natural light regime, and 8 of 10 spiders molted in the 14:10 L:D regime. Additionally, fifteen newly-emerged brown recluse spiderlings split into three cohorts of 5 spiders each in November exhibited more molting in the 14:10 L:D compared to natural and 10:14 L:D light cycles. Chilean recluses showed no differences in molting across the three photoperiod regimes. This species difference may be explained in that brown recluses are native to temperate zones where winters can be fatal; Chilean recluses are tropical where short photoperiods may have little significance for survival.
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Vol. 45 • No. 3