The Tabanidae (Horseflies) of Minnesota with Special Reference to Their Biologies and Taxonomy

University of Minnesota Agricultural Experiment Station The Tabanidae (Horseflies) of Minnesota With Special Reference to Their Biologies and Taxonomy Cornelius B. Philip Division of Entomology and Economic Zoology UNIVERSITY FARM, ST. PAUL CONTENTS Part One Page I. Introduction 3 Historical 3 Economic status 5 Disease transmission 0 II. Biological discussion 12 Representative life-history 12 Early stages of other species 25 Bionomics of adults 39 Seasonal and geographic distribution 47 Climate and topography of Minnesota 63 Environmental resistance and tabanid population 64 Physical factors 65 Biotic factors 67 Preventive and protective measures 69 III. Literature cited 7o Part Two IV. Systematic treatise 77 Taxonomy of adults 77 Keys to immature stages 79 Summary 125 V. Taxonomic references '7 THE TABANIDAE (HORSEFLIES) OF MINNE- SOTA WITH REFERENCE TO THEIR BIOLOGIES AND TAXONOMY CORNELIUS B. PHILIP* PART ONE I. INTRODUCTION Of all the blood-sucking insects, the mosquitoes and perhaps the tsetse flies in Africa alone surpass the Tabanidae in economic importance when all factors are considered. Notwithstanding the omni- presence of horseflies in all parts of Minnesota, and their legion in some sections of the north during June and early July, very little information is at hand concerning the tabanid species involved or regarding their habits and the manner of their development. Yet such data are almost prerequisite to rational measures for alleviating this scourge. The family includes the flies popularly referred to as horseflies, gad- flies, breezeflies, mooseflies, bulldogs, klegs, deerflies, earflies, and so on, according to the locality. Most of these names are restricted in use to the larger horseflies of the genus Tabamts. Greenhead is a term applied in this state to Tabamts lineola, and in the Northwest to T. sep- tentrionalis, altho different species of the genus go by that name in other parts of the United States. Bulldogs and mooseflies are local names used in the north in referring to the species of the affinis group of Tabamts, a group of red-sided horseflies that will be discussed later. The smaller flies of the genus Chrysops are commonly known as deerflies or earflies. In some sections of the north woods they are called pineflies because of their particular abundance in and about the edges of the forests and woods. The species of these two genera are the only horseflies of importance occurring in the state. Haematopota americana is reported by Cameron (1918)1 to settle on both stock and people in Saskatchewan, and has been so observed by the writer in Montana, but in Minnesota it is of very infrequent occurrence, being found in the northern part of the state only, where it is of no consequence economically. HISTORICAL That the Tabanidae were prominent among the problems of the early settlers in the state is well shown by the attention they received from Dr. 0. Lugger, the first state entomologist of Minnesota. In his * Now with the U. S. Public Health Service, Hamilton, Mont. 1 Dates in parenthesis refer to titles in the list of literature cited at the end of Part I. 4 MINNESOTA TECHNICAL BULLETIN 80 second report (1896), he mentions the trouble caused by these pests in various parts of the state and gives a very vivid account of their prevalence. C. V. Riley (1887), in referring to tabanids as a pest of stock, states that "in parts of the Mississippi Valley it is impossible to work horses in midsummer without protective covering, and in more northern regions even cattle have to be covered." When flies are abundant, not only the domesticated stock suffer because of their insatiable appetite for blood, but in the words of Lugger (loc. cit.), "moose and deer lose all fear of man and plunge into rivers and lakes to escape their attacks; they soon become very poor, as they have no rest to feed excepting at night." His meager data relative to life histories and to the species concerned afford a good index to the status of the study of the family at the beginning of this century. Washburn (1905) discusses the family in his report on the Diptera of Minnesota, summarizing in brief the limited information concerning the habits and biologies of horseflies at that time. His remarks are supplemented with a list of 20 species taken in the state. C. W. Howard, in the summer of 1914, again initiated a study of the Taban- idae. If was continued during the following two years as a project of the Minnesota Agricultural Experiment Station, with emphasis on the possibilties of transmission of swamp fever of horses. A brief report of his preliminary work will be mentioned more specifically later. A series of unfavorable seasons, and lack of funds, caused the study to be discontinued. Because of continued annoyance from the pests, the Tabanidae were again made the subject of an experiment station project in 1924. It is interesting to note the similarity in the history of the horsefly project in Louisiana, where the probable dissemination of anthrax, instead of swamp fever, enters in to make doubly urgent the need for a study of the flies as stock pests in that state. Following productive preliminary studies by Professor Hine, the project was discontinued until reopened in 1920 by Jones and Bradley. This study is in line with a project already established in Minnesota, therefore, and was suggested to the writer by W. A. Riley. To him and to other members of the Division of Entomology of the University the writer is deeply grateful for numerous suggestions and aids during the course of the work. J. S. Hine has identified or confirmed a few of the more difficult specimens noted in the systematic portion of this paper, and thanks are also due J. M. Aldrich and A. B. Gahan, of the National Museum and the Bureau of Entomology, respectively, for de- terminations of parasites reared during the investigation: A. K. Fisher, of the United States Bureau of Biological Survey, has generously sup- plied a list of the tabanids consumed by birds as compiled in their studies up to April, 1925. The study has also been greatly facilitated THE TABANIDAE OF MINNESOTA 5 through exchange of pertinent species with many persons of whom space does not permit full mention. Acknowledgments would not be complete without mention of the continuous invaluable and sympathetic aid afforded by my wife during the accumulation of the data and their subsequent presentation. ECONOMIC STATUS The Tabanidae occupy a position more or less overlapping the fields embracing economic insects of purely agricultural importance and those of pathological interest as affecting both man and animals. No end of problems are thus continually arising of a varied nature which their cos- mopolitan distribution enhances. Some reference has already been given to the economic importance of tabanids in the earlier history of the state. They constitute the worst pest of stock we have in the northern sections, where they fairly swarm for about four weeks during the early part of the summer. The severity of an outbreak can be appreciated only by actual observation. Similar abundance apparently occurs in Louisiana, of which Newell (see Hine, 1906) says "It is doubtful if any of the scientists who have touched, in their publications, upon the importance of these insects or upon their role in the dissemination of disease have had even a remote conception of the enormous numbers of these flies which at times infest certain of the coast and alluvial sections of Louisiana." Hine (1907), speaking of visiting a heavily infested swamp near Baton Rouge, mentions that . since that time (I) have had a much better idea of the injury that may be caused by horseflies than I ever had before. One would fail in an attempt to describe the exact conditions for to be fully appreciated they must be seen." In infested sections of Minnesota not only is diversified farming hampered, but stock raising and dairying are rendered extremely difficult. Howard (1916) states that "in places where farmers are trying to build up dairy farms, the presence of these flies has reduced the milk supply as much as 66 per cent in two weeks and in three nearly Ioo per cent." It is realized that derivation of statistics of this type are extremely difficult, and in a good many cases the statements of the dairymen and farmers themselves must be relied upon solely for judg- ment of the factors involved. In many parts of the state, however, dairying is the chief agricultural pursuit, especially where the land is more suited to grazing and pasture than to cultivation. A considerable portion of the northern half of the state consists of muskeg, a boggy type of land, interspersed with numerous lakes and open bodies of water. Not only is this a difficult type of land to farm, but it furnishes an idehl environment for the breeding of horseflies, and in such numbers as to make one of the best suited types of farming, 6 MINNESOTA TECHNICAL BULLETIN 80 namely dairying, unprofitable or even impossible. In parts of Roseau County dairying has had to be discontinued during certain seasons because of horsefly activities. An extreme case of this nature is quoted from Portschinsky (see Fraser, 1920), to the effect that, in northern Russia, agricultural operations must be carried on at night in the summer time, and in parts of Siberia, such as the shores of the River Om, settlers have been compelled to abandon the zone infested by horseflies because of their abundance. Trips were made by the writer to International Falls during the summer of 1924 and to Roseau County in 1925 for the purpose of mak- ing observations during the period when the horseflies were most abundant.

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