Flying sand-dwelling spiders: aerial dispersal in Allocosa marindia and Allocosa senex (Araneae: Lycosidae)

Aerial dispersal in spiders or ballooning is typically considered to occur during the day by juvenile instars or small-sized adults. Allocosa marindia Simó, Lise, Pompozzi & Laborda, 2017 and Allocosa senex (Mello-Leitão, 1945) are two nocturnal wolf spiders that inhabit coastal sandy beaches of South America. As mothers of both species emerge from the burrows during the night to disperse the spiderlings, we expected that aerial dispersal of spiderlings could occur during that period. Our aim was to test ballooning occurrence in both species during day and night under laboratory conditions, using as a positive control, the wolf spider Schizocosa malitiosa (Tullgren, 1905). We examined ballooning behavior of once-molted spiderlings of A. marindia, A. senex and S. malitiosa, under diurnal and nocturnal conditions, recording observations in a container with grasses and sand as substrate. We exposed the spiderlings to air flow and recorded occurrences of climbing the grass, dropping on dragline and tip-toeing (pre-ballooning behaviors). The three species performed pre-ballooning behaviors during the day but also in the night, and the occurrences of these behaviors varied both within and among species. More events of pre-ballooning behavior were observed during the day than during the night. However, we found differences in the number of events of tip-toeing and dropping on dragline according to the time of the day. We discuss the possibility that microhabitat conditions could affect ballooning propensity particularly in the three coastal wolf spiders.