380 



HOUSEHOLD INSECTS 



to the bird lice. There are several species of the family 

 Psocidse occurring in dwelling-houses, but none of them 

 except this one apparently ever becomes numerous enough 

 to attract attention. It is only under extraordinary con- 

 ditions that this book-louse becomes abundant enough to 

 deserve notice. All of these house psocids are wingless 



insects low in the scale of de- 

 velopment and usually quite in- 

 significant. 



This tiny book-louse (Fig. 132), 

 together with another closely re- 

 lated species, is widely known as 

 the " death-watch." It has long 

 been held that these small insects 

 are capable of making and do 

 make a ticking noise similar to the 

 Anobium beetle discussed in a later 

 chapter. Many entomologists find 

 it difficult to believe that such 

 small and frail insects are capable 

 of producing a sound audible to the human ear. They 

 are of the opinion that the sound attributed to the 

 psocid is really made by the Anobium beetle. This 

 beetle lives in burrows in old wood and the book-louse 

 is often found running about in the vicinity. It would 

 be very natural to ascribe the ticking of the invisible 

 beetle to the psocid which could be seen. It is said, 

 however, that there is a marked difference between the 

 sounds made by these two insects. 



The Rev. W. Derham, an English rector and a careful 

 observer, wrote an account many years ago of his obser- 

 vations on the ticking of the psocids. He says, "I am 



Fig. 132. — The common 

 book-louse, enlarged. 



