THE HOUSE FLY 73 



wings nearly without veins, covered with minute hairs ; highly bene- 

 ficial insects, living in the eggs of other insects. 



Chalcididae. Chalcis flies. 



.Small, generally polished, metallic; hind thighs frequently thick- 

 ened; antennae six to fourteen jointed, elbowed; wings often with 

 but few veins; beneficial, parasitic. 



Cynipidae. Gall flies. 



Small; abdomen compressed, short, second or second and third 

 segments much broader than the remaining; a long, slender ovi- 

 positor lying concealed in a ventral groove; antennae straight, thir- 

 teen to sixteen-jointed. 



Tenthredinidae . Saw flies. 



Head, thorax and abdomen less markedly distinct than in other 

 Hymenoptera ; wings large and broad, many cross veins ; antennae 

 straight, filiform, clavate or pectinate; ovipositor saw like; larvae 

 caterpillarlike, living on leaves, and known as slugs. 



Uroceridae. Horntails. 



Bodies cylindrical with parallel sides, long; antennae long, fili- 

 form, rather stout; ovipositor stout, exserted, attached to middle 

 of abdomen, and extending beyond the tip of body; larvae very 

 destructive wood borers. 



THE HOUSE FLY 



Musca domestica 



General Characteristics. — Notice the method of union 

 of the head with the thorax and the thorax with the abdo- 

 men. Observe the covering of the body. Of what use is 

 the hair? Note the markings of the body. How many 

 segments in the abdomen ? Do you find an ovipositor ? 



The Head. — (i) Note the large surface covered by the 

 eyes. Do you find simple eyes? Remove the head, plac- 



