Thermal Tolerances and Preferences of Some Dune-Living Spiders

Spiders from dunes in south Sweden were studied. The resistance to low temperature was studied by slow cooling and exposure to a constant temperature for 72 h. In winter the lethal temperature LT5o ranged between -6.7? and -20.9? in eleven species, in summer between -6.8? and -1 1.1?. Clubiona similis increased its tolerance with 6.70 before winter. Specimens of fifteen species were exposed to temperature rising 0.50 per minute in closed vials in water to fix the highest paralysing temperature. The species showed a variable tolerance, extreme values being 37.40 and 46.40. The thermopreferendum coupled with the humidity range and the evaporation preference was determined by use of a circular copper arena surrounded by a plexiglass cover with a temperature gradient between 90 and 40?, a humidity gradient from 98 to 30% RH and an evaporation gradient from 0 to 22 * 10-2 ml/cm2/h. Narrow evaporation zones were found. Stemonyphantes lineatus chose the coolest part around 140 and the wettest around 93% RH, when evaporation was about 0.3 * 10-2 ml/cm2/h. Phrurolithus festivus and Euophrys frontalis preferred the warmer around 270 and the drier around 63% RH, when evaporation was 6.8 10-2 ml/cm2/h. There was no correlation between the size of the spiders and their thermal behaviour, nor between the temperature preferred and the limits and amplitude of the temperatures tolerated.