Air Temperature and Humidity at the Bottom of Desert Wolf Spider Burrows Are Not Affected by Surface Conditions

SIMPLE SUMMARY: We investigated whether trapdoors, which small Negev Desert wolf spiders (Lycosa sp.) use to close their burrows, serve to maintain favorable conditions of temperature and humidity within them. We removed trapdoors from burrow entrances and monitored changes in temperature and relative humidity in their bottoms, where the spiders reside during the day. We also followed the behavioral responses of these spiders to trapdoor removal at different times of the day and in different seasons and monitored temperature and relative humidity in artificial burrows during summer mornings and at midday. At noon, air temperature at the bottom of open artificial burrows increased by less than 1 °C more than in covered ones, and total humidity remained constant, even though air temperature at the soil surface reached 55 °C when the burrow temperature was 35 °C. The relatively small increase in air temperature in uncovered burrows at midday was probably due to the penetration of direct solar radiation. Thus, it is evident that the presence of a trapdoor has a negligible effect on the microclimate at the bottom of these spiders’ burrows and its roles are more likely predator avoidance and prevention of flooding and stones and sand from falling in. ABSTRACT: Burrows are animal-built structures that can buffer their occupants against the vagaries of the weather and provide protection from predators. We investigated whether the trapdoors of wolf spider (Lycosa sp.; temporary working name "L. hyraculus") burrows in the Negev Desert serve to maintain favorable environmental conditions within the burrow by removing trapdoors and monitoring the ensuing temperature and relative humidity regime within them. We also monitored the behavioral responses of “L. hyraculus” to trapdoor removal at different times of the day and in different seasons. “L. hyraculus” often spun silk mesh in their burrow entrances in response to trapdoor removal during the day, possibly to deter diurnal predators. The frequency of web-spinning peaked on summer mornings, but spiders began spinning webs sooner after trapdoor removal later in the day. In addition, we monitored temperature and relative humidity in artificial burrows in the summer during the morning and at midday. At noon, air temperature (T(a)) at the bottom of open burrows increased by <1 °C more than in covered burrows, but water vapor pressure in burrows did not change. The relatively small increase in T(a) in uncovered burrows at midday can probably be ascribed to the penetration of direct solar radiation. Thus, air temperature and humidity at the bottom of the burrow are apparently decoupled from airflow at the surface.