Nocturnal, diurnal, crepuscular: activity assessments of Pisauridae and Lycosidae

Abstract

Animals are commonly categorized as diurnal, nocturnal, or crepuscular depending on the times of day when they are most active. These categories, although convenient, would be more useful if we knew more about how closely animal activity conformed to the labels. Similarly, if we knew more about the degree of nocturnality or diurnality of a particular species, we would have increased understanding of the selective forces acting on it. To clarify the intensity of nocturnality or diurnality in lycosoid spiders, we measured activity in 46 spiders divided among three congeneric species of fishing spiders (Pisauridae) and five species of wolf spiders (Lycosidae), in an austere laboratory setting. Overall, the three pisaurid species, pooled, were less than half as active as the five lycosid species, also pooled. All three species of fishing spiders and four of the five species of wolf spiders were strongly nocturnal in their activity. Only one species, the wolf spider Piratula minuta (Emerton 1885), was diurnal. None of the individual spiders that showed statistically significant nocturnal or diurnal activity (31 of 31 lycosids, 14 of 15 pisaurids) was purely nocturnal or diurnal. In all individual cases except for a single ambivalent Dolomedes tenebrosus Hentz 1844 (Pisauridae), statistically strong nocturnality was accompanied by substantial activity during the light hours, and statistically strong diurnality was accompanied by substantial activity during the dark hours. We discuss the overall low variability in activity patterns among the fishing spiders in comparison to the much higher variability among the activity patterns of the wolf spiders, the common but not ubiquitous presence of ultradian periodicities in individual spiders, and the significance of the fact that none of the individual spiders was strictly nocturnal or strictly diurnal.