Circadian clocks are vital to the proper functioning of organisms’ internal processes and behavioral outputs and typically have endogenous periods that approximate (within 1-2 hours) the 24-hour solar day. Clocks that deviate significantly from about 24 hours are often associated with metabolic syndromes or other disease states. For instance, organisms with near-24-hour clocks have higher survivorship under 24-h light:dark (LD) cycles than with 22- or 26-hour cycles. Likewise, mutant organisms with 22-hour clocks survive better under 22-h cycles but fare poorly under 24- and 26-h cycles. In other words, organisms suffer if their circadian clocks do not “resonate” with environmental cycles. Organisms fail to synchronize (entrain) their activity with non-resonant LD cycles and this failure typically leads to a number of physiological disruptions. Interestingly, several spider species have endogenous circadian periods that deviate by several hours from the period of the Earth’s solar day. The object of the present study is to investigate whether the phenomenon of circadian resonance also pertains to these atypical spider circadian rhythms. We investigated three spider species, two of which have internal periods (τ) significantly different from 24 hours. Approximately 50 individuals of each species of spider (Frontinella communis: τ=29.05±0.62 hours; Metazygia wittfeldae: τ=22.74±0.24h; and Cyclosa turbinata: τ=18.54±0.28h) were placed into chambers with periods of 19 (9.5:9.5h L:D), 24 (12:12h L:D), or 29 hours (14.5:14.5h L:D). If resonance is pertinent for spiders, we would expect survivorship to decrease in non-resonant LD cycles. Instead, no spider species exhibited decreased longevity in non-resonant L:D cycles. These findings contradict all previous research into circadian resonance and suggest that spiders do not suffer the costs of extreme desynchronization. In a second experiment, 10-11 spiders from each species were placed into infrared activity monitors to determine if their locomotor activity could entrain to (synchronize with) the three different LD cycles. Individuals from all three spider species entrained to all LD period lengths, again in contrast with prior research in other species. These results indicate that spider circadian clocks have highly unusual limits of entrainment and suggest a remarkable level of plasticity in their release from the selective pressure to maintain an internal period of approximately 24 hours.