432 APPENDIX I 



yellowish on the sides with a large gray triangle on the second 

 segment. Chrysops mitis has the abdomen entirely black, with 

 faint triangles of grayish hairs. Chrysops sordidus is distinguished 

 by having the first and second segments of the abdomen marked 

 with yellow on the sides, and the posterior margins of all the seg- 

 ments narrowly bordered with gray, and a dorsal row of small 

 triangles. The species are all of about the same size, a little less 

 than a half inch in length, C. excitans as a rule being a little larger 

 than the other two. 



The larger horse-flies are represented by at least six species, 

 all belonging to the group with hairy eyes. These were formerly 

 separated from the genus Tabanus and placed in the genus Therio- 

 plectes, but they are now united, the character used in separating 

 them being probably only of subgeneric value. The two most promi- 

 nent species are Tabanus flavipes, or the yellow-footed horse-fly, and 

 Tabanus zonalis, or banded horse-fly (PL, Fig. 2). They are nearly 

 three-quarters of an inch in ^length, with wings spreading an inch and 

 a quarter ; black, with the 'posterior margins of the abdominal seg- 

 ments bordered with a band of golden-yellow hair; the wings are 

 brownish, tinged with yellow toward the base. The two species 

 closely resemble each other, but can be readily separated by the 

 latter 's having the tubercle in front of the base of the wing reddish, 

 and the yellow bands of the abdomen broader, with slight ante- 

 rior projections on the second and third segments. The Tabanus 

 auripilus of northern Europe is closely related to flavipes. Another 

 species of about the same size is Tabanus affinis (PL, Fig. 3); 

 it is a dark brownish black, with the sides of the abdomen red. 

 The little-headed horse-fly, Tabanus microcephalus, is about one- 

 half inch in length ; the head is comparatively small, not exceeding 

 the width of the thorax; the abdomen is marked with three rows 

 of conspicuous grayish triangles. The northern horse-fly, Ta- 

 banus septentrionalis, is similar in general appearance, but with a 

 larger head and less prominent abdominal markings. The sixth 

 species, Tabanus illotus, is distinguished from the preceding one 

 by the broad, distinctly excised, third antennal joint, and faint 

 brown clouding on the cross-veins. 



The larvae of the horse-flies (Fig. 4) are aquatic or subaquatic, 

 living either in the mud in streams and swamps, or in wet earth 

 adjacent to springs. The eggs are placed on plants overhanging 

 the water or in very wet situations. The eggs hatch in about a 

 week, and the young larvae drop into the water or mud. The 

 larvae are carnivorous, feeding upon other insects and snails, and 

 probably repaying to some extent their annoyance when adult. 

 They are cylindrical, tapering gradually toward the end, and 

 usually translucent, whitish, and in some of the larger species 



