HOW TO KNOW THE IMMATURE INSECTS 



23a. Posterior spiracles situated upon the antepenultimate segment; 

 abdominal segments 1-6 subdivided, the body apparently consist- 

 ing of 20 segments exclusive of the head 24 



23b. Posterior spiracles situated upon penultimate segment; abdominal 

 segments simple, the body apparently consisting of 11 or 12 seg- 

 ments exclusive of the head 25 



24a. Posterior dorsal internal extension of head spatulate at apex; 

 ventral posterior projections in the form of 2 short sclerotized 

 rods. Fig. 553 Family THEREVIDAE 



About 300 species have 

 been described. The larvae 

 T^n^r^rnTTTTsr-^^ V frequent sandy soil, fungi 



=i^^^4^^'?4^<^^-'-^^^ ^^^ decaying wood. They 



feed upon earthworms and 

 Fig. 553. Psilocepholo hoemorrhoidolis O*^®^ Soft-bodied insectS OI 



Macquart. decaying organic matter. 



The adults are known as 

 stilleto flies. 



24b. Posterior dorsal extension of head not spatulate at apex; ventral 

 posterior projections absent. Fig. 554 Family SCENOPINIDAE 



Fig. 554. Ventral 

 aspect of head of 

 Scenopinus fenes- 

 tralis L. 



About 50 species have been described. The 

 larvae ore sometimes found in houses under car- 

 pets or in furniture and also in decaying wood. 

 Their food habits are thought to be predacious. 

 One species is thought to destroy the larvae of 

 carpet beetles. 



25a. Penultimate abdominal segment longer than ultimate, with a deep 

 transverse depression near its apex giving it the appearance of 

 2 distinct segments; ultimate segment terminating in a sharp ridge 

 with a median sharp point, on either side of which dorsally and 

 ventrally are situated 4 very closely approximated; hairs. 

 Fig. 555 Family MYDAIDAE 



Around 100 specie.« have 

 been described. Both adults 

 and larvae are predacious. The 

 larvae are found in decaying 

 wood. The adults are known as 

 m'ydas flies and ore often con- 

 spicuously marked. 



Fig. 555. Mydos clovotus Drury. 



198 



