XIII . STRIDULATING ORGANS 3 
i) 
N 
spiders possessing them certainly do not seem to form a 
natural group. 
Stridulating Organs—When Arthropod animals are capable 
of producing a sound, the result is nearly always obtained by 
“stridulation,” that is, by the friction of two rough surfaces 
against each other. The surfaces which are modified for this 
purpose form what is called a “stridulating organ.” Such 
organs have been found in three very distinct Spider 
families, the Theridiidae, the Sicariidae, and the Aviculariidae. 
Hitherto they have only been observed in three positions— 
either between the thorax and abdomen, or between the 
chelicerae and the pedipalpi, or between the pedipalpi and 
the first legs. 
In the Sicariidae and the Aviculariidae, the sounds have 
been distinctly heard and described. Those produced by the 
Theridudae would appear to be inaudible to human ears. 
Westring ' was the first to discover (1843) a stridulating 
organ in the small Theridud spider Asagena phalerata. The 
abdomen, where the pedicle 
enters it, gives off a chitinous 
collar, which projects over 
the cephalothorax, and has 
the imner surface of the 
dorsal part finely toothed. 
When the abdomen is raised 
and depressed, these teeth 
scrape against a number of 
fine striae on the back of 
the posterior part of the 
Rs Fic. 183.—Stridulating apparatus of Steatoda 
cephalothorax. A similar bipunctata, 6. Muchenlarged. A, Ridged 
organ has been sinee found and toothed abdominal socket ; B, striated 
‘ : : : area on the cephalothorax ; C, profile of 
in various allied spiders, of tne spider, x5. 
which the commonest Eng- 
lish species is Steatoda bipunctata. In this group it is generally 
possessed by the male alone, being merely rudimentary, if present 
at all, in the female. 
In 1880 Campbell? observed that in some of the Theridiid 
Spiders of the genus Lephthyphantes, the outer surface of the 
1 Nat. Hist. Tidsskr. iv., 1843, p. 349. 
2J. Linn. Soc. xv., 1881, p:. 155. 
