92 OUTLINES OF ENTOMOLOGY. 



Each of these divisions contains many families which differ in 

 many points of structure and habit. It will be possible here to refer 

 only to those which include the species most commonly met with, and 

 of most importance from an economic standpoint. In the first we find 

 the Gall-gnats and grain-flies (Cecidomtii)^). These are all small 

 species, which are injurious to vegetation. They have slender bodies 

 and long antennae, which are often plumy. The wings have three or 

 four veins, extending from base to outer margin, and are usually 

 fringed around the edge. The halteres are long and round-knobbed, 

 and the legs long and slender. The gall-making species place their 

 eggs upon leaves or tender stems, into the tissues of which the larvae 

 work their way, causing by irritation, peculiar fleshy or woody swell- 

 ings. On this abnormal vegetable tissue the larvae feed. The latter are 

 minute maggots, often of a pale red color, with a peculiar, clove- 

 shaped dark mark on the under side near the head, which can be 

 clearly distinguished only by the aid of a lens. 



The Hessian fly {Cecidomyia destructor, Say.) and the Wheat-midge 

 [Dlplosis tritici, Kirby) are the most notoriously destructive of these 

 gnats. The larvae of the former are flesh-colored maggots, which are 

 found beneath the sheaths of the lower joints of the wheat stalk in au- 

 tumn and early spring, and which dwarf and sometimes entirely kill the 

 plant by extracting the sap from the tender stems. In the change to 

 pupa, the larval skin hardens and turns brown, forming a "flax-seed"- 

 like pupariunij within which the transformations take place. 



The Wheat-midge is a tiny, orange-colored fly which places its eggs 

 on the young heads of wheat, from which the red maggots extract the 

 iuices and cause the kernels to shrivel. 



The Buftalo-gnats (Simulid^) are short, thick species with a very 

 rounded thorax, short antennae and strong mouth parts, capable of 

 drawing blood from cattle and mules as well as from man. At certain 

 seasons of the year they are an almost insupportable pest on the shores 

 of the northern lakes and in the south, along the principal water- 

 courses. The larvae breed in water and have a singular feathery gill at 

 the hinder end. 



Mosquitos (Culicid^) are characterized chiefly by the complex 

 mouth parts, which are projected straight forward in front of the head. 

 The beak or sting of the female mosquito — for the males are inoffen- 

 sive creatures, that neither sing nor sting — when closely examined, is 

 seen to consist of a bundle of fine bristles, seven in number, which to- 

 gether form a sharp-pointed tube by which the skin of man and the 

 larger animals is pierced, and through which a minute portion of poison 

 from a gland in the pro-thorax is forced into the wound, before or after 



