. Bulletin. Science; Natural history; Natural history. 32 BULLETIN SOUTHERN CALIFORNIA ACADEMY OF SCIENCES VOLUME 74. TIME, HOURS Figure 2. Graph showing number of P. scabcr caught in traps as an indication of relative activity level on three successive nights, April 30 to May 3, 1973. Lines above show the relative humidity (RH), and tem- perature 5 cm above the ground in the Meseinbryantlwnnim habitat (TEMP). them to detect. Humidity may also be of im- portance, however; on the second night, and especially on the third night of study (when be- cause of heavy fog, the humidity remained close t
. Bulletin. Science; Natural history; Natural history. 32 BULLETIN SOUTHERN CALIFORNIA ACADEMY OF SCIENCES VOLUME 74. TIME, HOURS Figure 2. Graph showing number of P. scabcr caught in traps as an indication of relative activity level on three successive nights, April 30 to May 3, 1973. Lines above show the relative humidity (RH), and tem- perature 5 cm above the ground in the Meseinbryantlwnnim habitat (TEMP). them to detect. Humidity may also be of im- portance, however; on the second night, and especially on the third night of study (when be- cause of heavy fog, the humidity remained close to 100 percent) nocturnal activity continued until a later hour at night. Activity pattern of Steatoda grossa.—The activ- ity patterns of 76 S. grossa were monitored in the garage study area near Asilomar Beach. An atomizer which sprayed a very fine mist of water was used to delineate the extent of each web. The droplets adhered to the web without damaging it and without harm to the spider, and refracted the light brilliantly. Within 20 minutes evapora- tion restored the web to its original state. Each spider was observed every two hours over a 24 hour period. Spiders were scored as inactive if hiding in their daytime retreats, and as active if they were in a typical predatory stance in the web or were out actively moving about. Tempera- ture, relative humidity and light exposure were recorded every hour from one typical web. Dur- ing the night spiders were observed with a flash- light covered with a red filter, a procedure which appeared not to disturb them. There was much variance among the individual spiders with respect to their periods of activity. Some individuals were active in the predatory stance during the whole observational period; others were not active at all although they had been seen previously. However, on the whole the population showed much greater activity between sunset and sunrise than during the day (Fig. 3). Relative humidity and temperature showed a c
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