FIELD BOOK OF INSECTS. 



We have three cosmopolitan species of Necrobia. They 

 are known as Bone Beetles because they are usually found 

 on carrion after most of the flesh is gone, probably feeding 

 on other insects there rather than on the carrion. N. 

 rufipes (Plate LXXIX) is called the Red-legged Ham- 

 beetle from its frequent appearance in that staple. Herrick 

 says: 'When the larva gets ready to transform it makes 

 a curious and interesting cocoon in a rather novel way. 

 The larva leaves the fatty portions and gnaws its way 

 either to the harder, more fibrous parts of the ham or may- 

 be into a near-by beam. Here it makes a glistening white 

 cocoon that looks much like paper. The cocoon is not 

 made from silk like the cocoons of most insects, but is 

 composed of small globules of spit out of the mouth of the 

 larva. These globules adhere to each other and when 

 dry form the paper-like cocoon." The three species 

 may be separated as follows (none exceed a quarter of an 

 inch in length) : 



1. Pronotum and base of elytra red; rest of elytra blue 

 or green ; head and abdomen black ruficollis. 



No red on dorsal surface, but bluish 2. 



2. Legs and basal joints of antennas red riifipes. 



Legs and antennas dark violacea. 



Necrobia is one of those genera in which the fourth 

 tarsal joint is indistinct and the disk of the thorax is 

 separated from the flanks by a marginal line. In Trichodes 

 (front margin of eyes indented; antennal club triangular) 

 and Thaneroclerus (eye-margin not indented; the 3-jointed 

 antennal club gradually formed) the fourth tarsal joint is 

 of normal size (the first joint is very small and covered, 

 above, by the second; tarsal claws toothed). Trichodes 

 nuttalli (bluish, with reddish-yellow markings) and 

 Thaneroclerus sanguineus (brown, with red elytra) are 

 shown in Plate LXXIX. 



PTINID^E 



The small (.25 in. and less in length) beetles of this 

 family are so various that it is difficult to characterize the 

 family. The thorax usually extends above the head like 



320 



