Web-building time in a spider: preliminary applications of ultrasonic detection.

Data collection on time and length of building in orb-weaving spiders has suffered from absence of light during construction and inconvenient hours. A simple apparatus is described which permits recording of the spiders' movements as they disturb an ultrasonic field. By varying onset and length of dark periods for two animals at even temperature and by registering the building periods for 127 webs, a definite influence of the light-dark cycle can be identified: there is a strong preference for building webs in the dark; this is superimposed on the circadian rhythm of orb-web construction. One of the spiders always built earlier than the other.