Association of the Face Fly, Musca autumnalis with Bison in Western North America


Department of Entomology and Parasitology, University of California, Berkeley 94720

Reprinted from Annals of the Entomological Society of America, Vol 63, no. 3, May 1970, pp. 635-639


Musca autumnalis De Geer (Diptera: Muscidae) was a pest of bison at the National Bison Range, Moiese, Mont.. in 1966 and 1967, where flies occurred also around the eyes of deer, antelope, and horses. In 167 adults were reared and the immature stages were from bison droppings obtained at the Range.

Adults first were collected in 1967 from 4 widely scattered localities (from 6500 to 9245 ft) and several different habitats within Yellowstone National Park in Montana and Wyoming. Flies also were reared from and seen on cattle and their droppings near Gardiner, Mont (5300 ft), for the first time in 1967.

In 1967, 9 range bison at the Range exhibited eye disorders, ranging from discoloration to eyeball eruption (blindness). Such eye problems had not previously been observed in these animals. The difficulties inherent in managing these animals make it impossible to deal with eye disorders in bison as can be done with domesticated stock. The success of M. autumnalis in the absence of regular insecticide treatments of animals and its present and potential role as a pest of various big game animals in wildlife areas is discussed, as well as the prospect of reservoir populations of flies able to disperse out of wildlife areas into surrounding' agricultural areas.

As part of a study of the dipterous fauna associated with the droppings of North American ungulates Poorbaugh et al. 1968), the fauna of bison droppings initially were surveyed at the National Bison Range (N.B.R.) Moiese, Mont., in September 1966.

These various animals were observed being bothered by flies, later identified as the face fly Musca autumnalis De Geer, that remained around the eyes and noses of the animals. In 1967, additional observations were made at the N.B.R. and in and adjacent to Yellowstone National Park (Y.N.P.), to determine the extent to which M. autumnalis had established itself in these areas.

The dispersal of the face fly and its annoyance of cattle and other domesticated animals has been documented by many authors (see bibliography of Smith et al. 1966; Smith and Linsdale 1967, 1968) since its appearance in Nova Scotia in 1952 (MacNay 1952). However, the presence and potential significance of the face fly in wildlife areas have not been assessed.

Materials and Methods

The 2 principal study areas were the N.B.R. and Y.N.P. in Montana and Wyoming. The former is a 18,500-acre area situated at the southern end of the Flathead Valley in Lake and Sanders Counties, Mont. Here the elevation at the headquarters, where most work was done, is 2585 ft. The vegetation consists mainly of grasses and forbs, with a few trees near Mission Creek, a stream running behind the headquarters area and along the exhibition pasture fences. Within the boundaries of the N.B.R., the terrain varies from dry grassland to scattered stands of Douglas fir and western yellow pine slightly above 3000 ft.

In general, characterized as a series of rolling, forested plateaus surrounded by higher mountains that are at the northern end of the central Rocky Mountain chain. The general elevation of ca. 7500 ft, although the northern portion has some open sagebrush-grassland valleys at ca. 5900-6600 ft. The park encompasses ca. 2.2 million acres. Collections and observations were made at the N.B.R. on 24 Sept. 1966 and 27 May and 20 July 1967. At Y.N.P., studies were conducted from 8 June to 28 Sept. 1966, and from 18 May to 8 Oct. 1967.

In addition to these wildlife areas, collections of Diptera or cattle droppings, or both, were made at a small ranch near Gardiner, Mont., on 8 occasions in 1966 and on 11 dates in 1967. This ranch, near the north entrance of Y.N.P., is situated in a semiarid valley, where maximum summer temperatures are often above 90°F.

Flies routinely were collected with an insect net from vegetation, buildings, and animals. A small hand net (8 in. diam) usually was used to collect flies from around the eyes of animals. In addition to the collected specimens, numerous face flies were observed at close range ( 1-3 ft) and at greater distances with 8x binoculars or with a 15-60x zoom-type spotting scope, while clustered on the faces of animals.

Individual droppings of bison, moose, elk, cattle, and other animals were collected and transported to a laboratory where they were processed. The cattle and bison droppings were cut into 8 equal parts, after which alternating slices were placed in a rearing container and in a portable Tullgren funnel apparatus for extraction of larvae into 70% ethanol. The rearing container consisted of a 1-gal cardboard carton lined with a polyethylene bag and contained a 1-in. layer of vermiculite on the bottom. After receiving a dropping the carton was sealed with a lid of nylon mesh having a plastic tube in the center that led to a pint collecting container. The emerged adults were collected periodically from the latter container and pinned for subsequent examination.


Collections and Observations at the N.B.R.-M. autumnalis was first collected here by one of us (J. F. B.) on 24 Sept. 1966, when 19 female and 11 male were collected from a cow bison and a horse, and from vegetation and automobiles parked near the exhibition pastures. Face flies were observed also on the faces of a pronghorn antelope and a mule deer on this date.

The cow bison was observed for about an hour during which there were 20-30 M. autumnalis rimming the lower edge of each eye and probing the fluids exuding from the irritated eyes. A few scattered flies were seen around the nose, sides of the face, and top of the head but, as Jones ( 1963, noted) for cattle, most of the flies aggregated around the eyes. The cow held her head very close to the ground periodically attempted to dislodge the flies by shaking her head and by rubbing her head and face in the grass or against a fence post. In all instances M. autumnalis would fly around her head in a small cloud and immediately land again around her eyes. Only by rubbing her head in the grass could animal dislodge the flies for any length of time.

The cow's eyelids were swollen and the inner corners of both eyes were purulent. There also were crusts of dried fluid around both eyes. The cow appeared listless and continually dropped her head into the grass, but did not feed. The eyes of the horses at the N.B.R. also were swollen and red, probably because of the feeding flies. Hansens (1961) reported that as few as 5-10 flies/animal caused irritation to the eyes.

In 1967, face flies were seen resting on buildings and in the grass on 26 May, but there were few flies (less than 2/animal) bothering bison or horses at this time. Mr. J. P. Mazzoni, Refuge Manager of the N.B.R., stated that the flies had been active for about 1 week, but that they were not so abundant as they had been at a comparable time the previous year.

On 20 July 1967, a group of 20 bison in the exhibition pasture near headquarters was observed almost continuously from 1400 to 1700 hr. MST. During this time (at a temperature of 84°F) the cows had ca.. 25-30 flies/animal, bulls 20-25, and calves 10-15.

On all animals the flies were scattered over the faces from the eyes to the tips of the noses. They appeared to be feeding on both eye and nasal secretions. On a few animals, the flies were essentially evenly distributed over the faces, but they usually were concentrated around the eyes or noses; most were aligned along the lower edges of the eyes.

Besides the avoidance reactions previously mentioned for the bison cow, the animals observed in 1967 also dusted themselves in well-used wallows. This behavior provided some temporary relief from the flies. Some bison also attempted to discourage flies by keeping their eyes tightly shut while standing together in a compact group and rubbing their heads against each other. Treece (1960) previously reported that cattle would huddle together with their heads in the center of a circle to avoid M. autumnalis.

In addition to the flies on the animals, females were seen resting in the grass and on the wire fence along the pasture. Less than 10% of the flies seen on the animals were males. and no males were seen or swept from the grass. In a plot of ca. 100ft within the exhibition pasture and ca. 1500 ft from the bison group, a series of 10 samples (each consisting sweeps with an insect net) yielded 1.2 M autumnalis sample; all were females. At ca. 1500 hr, male face flies were observed on the leaves and branches of brushes and trees ca. 2 miles from and 1000 it higher the exhibition pastures, where only females had been collected earlier. Sweep net collections from bushes contained only male face flies. In this instance then, most males, perhaps those in certain age groups, were spatially isolated from the females for at least part of the day. When females were active in the grass and on the bison in the unshaded lower pastures, most males were observed resting in shaded areas at higher elevations. The disproportionate sex ratio of face flies on animals has been noted previously with pasturing cattle (e.g., Cheng et al.1962, Dobson and Matthew 1961, Hansens and Valiela 1967, Ode and Matthysse 1967, and Teskey 1969).

Adult M. autumnalis were first reared from 3 of 4 bison droppings collected at the N.B.R. on 27 May 1967. The number of flies emerged per each half-dropping was 25, 9, 1, and 0, and the mean number of larvae extracted from the 4 half-dropping samples 6.5. On 20 July 1967, both of the 2 bison droppings collected were positive for M. autumnnalis. One of the half-pat samples produced 30 flies and the other 49. A malfunction in the Tullgren funnel apparatus prevented the recovery of larvae from these samples. In laboratory experiments, Bay et al. (1968) previously had found that the face fly would oviposit and undergo successful larval development in the feces of bison and several other animals.

Collections and Observations in Y.N.P. and Vicinity. In 1966 M. autumnalis were never observed on animals or seen on, reared, or extracted from animal dung collected either in Y.N.P. or at the ranch near Gardiner. During 1966, 12 cattle, 22 bison, and 24 moose droppings were collected for study, and cattle, horses, bison, moose, and other animals frequently were examined for flies between 8 June and 28 Sept. The cattle ranch was visited on 17, 21, and 27 June, 19 July, 3 and 15 Aug., and 2 and 11 Sept. 1966, whereas 1 or more of the other animals or their droppings were examined almost daily during the study period in Y.N.P.

Face flies apparently first reached this area during the summer of 1967. Two adults emerged from 1 of 4 cattle droppings collected near Gardiner on 19 July, but no adults were seen on cattle at that time. Prior to 19 July. no flies were observed on 21 May, and 5 and 16 June, and 2 droppings collected on 22 June were negative for face fly.

Adults were first seen around the eyes of cattle and horses (on the ranch near Gardiner on 10 Aug. 1967. M. autumnalis were seen on these animals on warm, sunny days through the remainder of August and to mid-September. During this period flies were seen on cattle on 4 of the 6 days the ranch was visited. Three flies/animal was the maximum seen on a given cow or horse, and usually there were only 1 or 2 flies/animal. Not all the animals observed had face flies on them at any given time. One of 2 cattle droppings collected here on 30 Aug. produced 1 fly, and 2 "older" droppings collected on 11 Sept. were negative.

The first M. autumnalis collected in Y.N.P. was a male captured in a CO2-baited Malaise-type trap used to attract and capture blood-sucking Diptera. This fly was captured 21 Aug. in an open sagebrush-grassland valley at 6500 ft. On 23 Sept., a female, one of three seen flying around Burger's horse, was collected with a net at Slough Creek Valley (6665 ft). This locality is similar to that of the 21 Aug. record. Six & also were seen feeding on a fresh horse dropping here. On 27 and 28 Sept., 2 % were collected in the same manner as on 23 Sept. The first was taken at 9245 ft in a spruce-fir forest, and the second at an elevation of 7160 ft on an open ridge top, surrounded by lodgepole and white bark or limber pine forest. No face fly larvae or emerged adults were collected from the 20 bison, 8 moose, and 6 elk droppings processed between 19 May and 1 Oct. 1967.

The 4 records of adult M. antumnalis in Y.N.P. covered a straight-line distance of 24.5 miles and an altitudinal spread of 2745 ft. The record nearest to Gardiner, where adults were first reared, from cattle droppings in July, was Slough Creek Valley, 26.5 miles SE of and 1400 ft higher than Gardiner.

The face fly is the 2nd fly pest of cattle that has successfully adapted to bison. The horn fly, Haematobia irritans (L.) , apparently has been associated with bison for a long time. In Y.N.P .they generally reached peak numbers on animals (ca. 100-200 flies/adult) during late August and September. During the same period there were ca. 20 H. irritans/bison at the N.B.R., but no horn flies were reared from bison droppings.

Effect of Face Flies on Bison.-In addition to the avoidance reactions described previously, eye complications in bison were first noted in 1966 when J. P. Mazzoni (personal communication) observed that the feeding flies were causing serious irritation to the eyes of bison in the headquarters exhibition pasture as well as to horses quartered in this general area. Eye irritations most commonly were manifested in a general redness of the eyeball accompanied by copious purulence.

The 1st cases of blindness in range bison were noted during the fall roundup and corral activities in October 1967 (J. P. Mazzoni, personal communication). At this time, 9 of 405 animals examined had eye disorders of various degrees of seriousness. The 3 most severely afflicted animals (J. P. Mazzoni, personal communication) were: (a) a large adult bull that was blind on 1 side and so impossible to manage that it had to be left in the field, (b) a 4-year-old cow with both eyes afflicted (blind on 1 side with the eyeball erupted) that constantly butted and hooked animals on her blind side while in the corral, and (c) a yearling heifer with both eyes affected and blind on 1 side with the eyeball erupted. As with outbreaks of pinkeye in cattle (Cheng 1967) there presently is only a circumstantial association of face flies with the various eye complications observed in bison. After increasing in abundance in each succeeding year since it was first noted in the Flathead Valley, the face fly population reached peak numbers in 1966 and 1967. Prior to 1966, blindness and "pinkeye" were unknown in the bison at the N.B.R. ( J.P. Mazzoni, personal communication).


Visual observations of animals and surveys of various animal droppings undertaken in 1966 and 1967 indicated that the face fly was much more abundant at the N.B.R. than in Y.N .P. The fly already was well established at the N .B.R, and throughout the Flathead Valley for 2-3 years prior to 1966, whereas it reached Y.N .P .and vicinity only in the fall of 1967. At the N,B.R., where M. autumnalis was present from about mid-May into early October, the face fly population had increased to a point where it was seriously interfering with management of the bison herd, and possible methods of insecticidal control were being considered (J.P. Mazzoni, personal communication) .Since the bison roam freely over the entire range ( 18,500 acres) , the present outlook for fly control is not good. The dust bag method, for example, which currently appears most promising for cattle treatment (Adkiris and Seawright 1967, Hair and Adkins 1965, Seawright and Adkins 1968, Turner 1965) does not appear feasible for wild horned bison.

Most bison recover from minor eye complications during the absence of the flies, but when constant irritation by flies persists during the fly season, eruption of the eyeball eventually occurs in some animals, resulting in permanent loss of vision. As it undoubtedly will not be possible (either financially or otherwise) to deal with pinkeye and other eye disorders in these wild animals as in domestic cattle, the face fly may prove to be a more serious menace to bison and other wildlife than to domestic stock.

Should the face fly become as abundant in Y.N.P. as it is at the N.B.R. its effect on wildlife could prove more serious than it now is at the N.B.R.. In Y.N.P., bison and other big game animals range over an area of ca, 2.2 million acres, much of it wilderness country. Therefore, except for the introduction and establishment of natural enemies, other methods of control in this area would probably prove too costly or unfeasible.

At present, M. autumnalis is not abundant in Y.N.P., and its recorded 1967 seasonal occurrence was brief, from late August to late September. Nevertheless, since it is now established on adjacent cattle ranches and was collected within the Park boundaries at widely differing elevations and habitats, the fly might well successfully adapt to the entire range of habitats within Y.N .P .and become permanently established. Some factors seemingly favoring its establishment are :

(1) Most bison tend to stay together in groups. There are at least 3 subunits of the herd in different areas of the Park with some contact and interchange between all of them (M. Meagher, personal communication) , and the droppings of these animals could produce flies at widely separated areas within the Park. In addition, the older bulls that no longer remain with the main herds are widely scattered throughout the Park, and their droppings would provide additional oviposition sites for wide ranging female M. autumnalis.

(2) The bison herds may remain in 1 area for a week or more. This behavior would permit populations of flies to remain with a herd long enough to oviposit in an area heavily concentrated with fresh droppings, and thus become as successful as the horn fly, which already has adapted to the bison.

( 3) Although face flies would require fresh bison droppings in which to oviposit (assuming that they also will not adapt to elk or moose droppings) the flies could feed on the many other wildlife species such as moose, elk, deer, and antelope, or their droppings.

Climate, the eventual establishment of biological control agents, and possibly the mating behavior of M. autumnalis appear to be the principal factors that would limit the sizes of fly populations in Y.N.P. Particularly at the higher elevations, hibernating adults may not be able to survive in large numbers because of low winter and early spring temperatures and a lack of suitable overwintering sites. Also. the usually mild temperatures characteristic of higher altitudes may hold the size of summer-fall populations in check during most years, In New York, Ode and Matthysse (1967) reported less flies on cattle during years having unusually cool summers.


The success of M. autumnalis in the absence of regular insecticide treatments of animals and its potential as a pest of various big game animals in wildlife areas should receive further study. The fly already is established as a pest of bison at the N.B.R. and if it becomes abundant in may affect even larger populations of wild ungulates there. The free-roaming nature of bison and other wild herbivores within such areas and the difficulties inherent in managing these animals make it impossible to deal with eye disorders as can be done with domesticated stock. Blindness of range bison, and possibly other animals, could become a new problem to deal with in wildlife management.

Now that the face fly is established with bison there will be reservoir populations of flies able to disperse out of wildlife areas into surrounding agricultural areas where insecticidal control measures are used, possibly reducing the effectiveness of these measures. At the present time the introduction and establishment of natural enemies of the face fly appears to be the most feasible method of control and the method most compatible with current methods of wildlife management.


We thank Mr. J.P. Mazzoni, Manager. National Bison Range; Mr. John McLaughlin, Superintendent of Yellowstone National Park, 1966; and Mr. R. Letegren, Acting Superintendent, Yellowstone National Park, 1967, for assistance and provision of Facilities during these studies, and Mr. W. Scott Chapman for permitting the work on his ranch. We gratefully acknowledge the enlightening personal communications of Miss M. Meagher, Park Naturalist, Yellowstone National Park, Mr. J. P. Mazzoni and Dr. D. K. Scharff, Montana State University.

References Cited

Adkins, T. R., Jr., and J. S. Seawright. 1967. A simplified dusting station to control face flies and flies on cattle. J. Econ. Entomol. 60 : 864-8.

Bay D..E., C. W. Pins, and G. Ward. 1968. Oviposition and development of the face fly in feces of six species of animals. Ibid. 61: 1733-5.

Cheng, T. H. 1967. Frequency of pinkeye incidence in cattle in relation to face fly abundance. Ibid. 60:9.

Cheng, T. H., D. E. H. Frear, and H. F. Enos, Jr. 1962. The use of spray and aerosol formulations containing R 1207 and dimethoate for fly control on cattle and the determination of dimethoate residues in milk. Ibid. 55: 39-43.

Dobson, R. C., and D. L. Matthew. 1961. Field observations of the face fly in Indiana. Proc. Indiana Acad. Sci. 70 : 152-3.

Hair, J. A., and T. R. Adkins, Jr. 1965. Dusting stations and cable backrubbers as self-applicatory devices for control of the face fly. J. Econ. Entomol. 58: 39-41.

Hansens, E. J. 1961. Face fly promises to become Number 1 cattle problem in Northeast. N. J. Agr. 43:-12.

Hansens, E. I. and I. Valiela. 1967. Activity of the face fly in New Jersey .J. Econ. Entomol. 60 : 26-28.

Jones, C. M. 1963. Research on the face fly during 1962. Proc. N. Cent. Br. Entomol. Soc. Amer. 18:53.

MacNay, C. G. 1952. New records of insects in Canada, 1952. Annu. Rep. Entomol. Soc. Ontario 83:69, 92.

Ode, P. E., and I. G. Matthysse. 1967. Bionomics of the face fly, Musca autumnalis De Geer. Cornell Univ. Agr. Exp. Sta. Memoir 402.91 p.

Poorbaugh, J. H., I. R. Anderson, and I. F. Burger. 1968. The insect inhabitants of undisturbed cattle droppings in northern California. Calif. Vector Views 15: 17-36.

Seawright, I. A., and T. R. Adkins, Ir. 1968. Dust stations for control of the face fly in South Carolina. J. Econ. Entomol. 61 : 504-4.

Smith, T. A., and D. D. Linsdale. 1967. First supplement to an annotated bibliography of the face fly, Musca autumnalis DeGeer, in North America. Calif. Vector Views 14: 74-76. 1968. Second supplement to an annotated bibliography of the face fly, Musca autumnalis DeGeer, in North America. Ibid. 15: 119-21.

Smith, T. A., D. D. Linsdale, and D. I. Burdick. 1966. An annotated bibliography of the face fly, Musca autumnalis DeGeer, in North America. Ibid. 13 :43-53.

Tesky, H. J. 1969. On the behavior and ecology of the face fly, Musca autumnalis (Diptera: Muscidae). Can. Entomol. 101: 561-76.

Treece, R. E. 1960. Distribution, life history and control of the "face fly" in Ohio. Proc. N. Cent. Br. Entomol. Soc. Amer. 15: 107.

Turner, E. C., Jr. 1965. Area control of the face fly using self-applicating devices. J. Econ. Entomol. 58: 103-5.

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