HORSE-FLIES AND WESTERN AGRICULTURE 25 



Larva. 



Like Tahanus punctifer, the larva of T. phaenops is ready to moll 

 upon hatching. The first exnvia are found soon after hatching in 

 the water into which the larvae have dropped. 



DESCRIPTION OF THE FIRST EXUVIXJM. 



The length of the first exuvium is 2.4 millimeters. The first to seventh 

 abdominal segments have an anterior margin of from 4 to 6 rows of spines. 

 The neck of the first thoracic segment is armed with spines. Spines are lack- 

 ing on the second and third thoracic segments. On each side of the venter. 

 midway on each thoracic segment, is a tuft of two long and one or two short 

 bristles, similar to the tufts on T. punctifer. 



DESCRIPTION OF THE SECOND IXSTAlt. 



The length of alcoholic specimens of T. phaenops is from 2.6 to 2.8 milli- 

 meters. The general color is white ; alcoholic specimens become pale yellow. 

 Every segment has fine longitudinal striations. The anterior end of the rirs 1 

 thoracic segment has a collar of yellow pile covering about a fourth of the 

 segment. Narrower margins of yellow pile encircle the anterior ends of the 

 second and third thoracic segments. On each side of the venter midway on 

 each thoracic segment is a tuft of three bristles similar to those in T. punctifer 

 except that in T. phaenops the bristles are of approximately equal length. A 

 few scattered bristles appear on each segment. 



Each abdominal segment has the six-spined protuberance or prolegs and 

 between these and continuing* in a strip beyond them over the dorsum are 

 spines slightly smaller. Around the middle of each abdominal segment are 

 scattered bristles. 



The anal segment is encircled anteriorly with yellow pile. The anus, 

 broadly elliptical in shape, has a margin of yellow pile. The siphon, which is 

 only half as long as the anal segment, has yellow pile around its folding an- 

 terior end. Around the opening of the siphon are numerous bristles. 



DESCRIPTION OF FULL-GBOWN LARVA. 



The full-grown larva (fig. 16. A; PI. II, E) is about 30 millimeters long. 

 General color dirty gray, shading sometimes to greenish or reddish. Arrange- 

 ment of propodia as in T. punctifer. 



Prothorax : Anterior portion back of collar smooth and shiny on all aspects. 

 Posteriorly, some striation shows on practically all aspects. 



Mesothorax and metathorax : Upon each dorso-latero-cephalic area the brown 

 of the anterior collar projects backward slightly, ending in a point. 



Sides of all abdominal, and mesothoracic and metathoracic segments strongly 

 striated. Siphon striated on all aspects. Dorsum of seventh and eighth s< g- 

 ments fairly smooth and shiny (posterior part of eighth striated). All others 

 striated with fine wavy lines between stria 1 ; sixth less strongly and distinctly 

 striated than those preceding it. 



On ventral aspect of abdominal segments the stria? are broken up into irregu- 

 lar wavy lines, except for an area directly anterior to anus, which is smooth 

 and shiny. 



On venter of each thoracic segment are two distinct hairs placed one at each 

 side and about midway between anterior and posterior margins of segment. 



Anus surrounded by light brownish pile. Longest axis transverse. The 

 siphon measures 0.5 millimeter. 



The most characteristic features of the living larva are the dirty gray 

 color, prominent prolegs, and strong striation of the sides of the abdominal 

 segments, especially the anal segment. 



Descriptions of larva made with the aid of a binocular microscope. 



Habits ok hie Larva. 



Larvae of Tab anus phaenops hatched in a vial of water remain at 

 the bottom of the water. The full grown larvae of this specie's were 



