SPIDERS 153 



its prey. The threads of which the web is constructed are not 

 adhesive, but a tangled mass of scaffolding above trips passing 

 insects which fall onto the sheet. Before they have time to recover, 

 the owner of the web has darted from its tube and gathered them 

 in. 



The comb-footed spiders of the family Theridiidae are for the 

 most part thickset, sedentary types that hang upside down from 

 their irregular maze-like webs. Most are small spiders suspending 

 their snares on plants with lines so fine that they are often un- 

 noticed, or hiding them in burrows or fissures in the soil and under 

 litter. 



The two-dimensional orb web of the Argiopidae is the crowning 

 achievement of the aerial spiders: it is the last stage in a series that 

 has resulted in a circular design. Finally, the Linyphiidae build 

 a horizontal platform upon which drop flying and jumping insects, 

 usually after being halted in mid-air by a superstructure of criss- 

 crossed lines guyed to adjacent vegetation. The spider clings up- 

 side down beneath it, runs over the surface with surprising 

 rapidity and pulls its prey through the webbing. A second sheet is 

 often present beneath the hanging spider and probably serves as a 

 barrier to attack from below. In numbers of individuals, genera 

 and species the Linyphiidae far exceed the total of any other 

 family of spiders in the temperate zones where they are the domi- 

 nant aerial types. The majority of these spiders are small, even 

 minute, and they occur in vast, little noticed numbers under soil 

 debris. Most of them are reddish or black creatures with somewhat 

 elongated bodies and legs set with fine spines, but there are 

 notable exceptions. The presence of a stridulating file on the side 

 of the chelicerae and a scraping spine on the femur of the pedipalp 

 serves to differentiate them from the orb weavers. 



The spider fauna of the British Isles comprises some 24 families 

 with over 570 species, nearly half of which are Linyphiidae. The 

 population in late summer has been conservatively estimated by 

 Bristowe (1939)* at some 2J millions per acre. He has calculated 

 that if all the spiders from an acre of land were to combine to build 

 one continuous thread, they would produce a strand in a single 

 day's spinning that would just about circle the world at the 

 equator: after ten days it would be long enough to reach the moon. 



