HORSE-FLIES AND WESTERN AGRICULTURE. 33 



Digging with a shovel about the entrance to the tunnel, larvae, 

 cocoons, and a few adults of the species were found about a foot 

 below the surface. Recently formed cocoons always had a mass of 

 Tabanus fragments and in some cases fragments of other flies stick- 

 ing to them. In the nest was also found a perfect male specimen of 

 Tabanus insuetus and a perfect male T. phaenops. The predator, 

 judging from reports of residents, is not annually abundant. It 

 was rather scarce in 1916 and quite abundant in 1917. It is an inter- 

 esting fact that in 1916 tabanids were more abundant than in 1917. 

 Because of a scarcity of T . phaenops in the midsummer of 1917, it 

 was believed that this predator, on account of its abundance that 

 season, was a very effective check to the species. Bembex did not 

 occur and T . phaenops was quite abundant in Bridgeport Valley 40 

 miles southwest and at a higher elevation. 



It was decided to attempt transportation of Bembex from Ante- 

 lope Valley to Bridgeport Valley. With nets 50 adults of the wasp 

 were captured on July 23, 1917, and placed alive in two small cages 

 about a foot square with bottoms covered with sand and gravel. In 

 these cages they were taken hurriedly by automobile to Bridgeport 

 Valley. About 35 survived the trip and were released at a place 

 resembling the breeding places in Antelope Valley. Seven or eight 

 cocoons of the species collected July 19 were placed there in gravel 

 at the same time. Sufficient observations were not made there the 

 following season to determine the result. In 1918 and 1919 the wasps 

 were very scarce in Antelope Valley. 



A close observation was made in 1919 of an attack on a female 

 Tabanus phaenops by one of these wasps. The fly was feeding on a 

 horse near the shoulder. Suddenly the wasp swooped down on the 

 fly, grasped and stung her, and flew away, leaving the fly in feeding 

 position. The fly was immediately paralyzed, so that she did not 

 withdraw her mouthparts from the host. Her legs seemed no longer 

 to grasp the hair of the horse and she was suspended by her mouth- 

 parts only. Removed from the horse, she seemed lifeless, except 

 for a few quiverings of the legs. The wasp was seen no more. 

 Undoubtedly this predator accomplishes considerable repression 

 of the horse-flies, but in view of the data in hand can not be consid- 

 ered a major factor. 



Stomachs of several species of insectivorous birds were exam- 

 ined without finding larvse or adults of Tabanidae, a result probably 

 not representative, since the Biological Survey has found horse-flies 

 or their larvse in the stomachs of no fewer than 78 species of birds. 



PROTECTION OF ANIMALS. 



Horses and cattle in pasture or on the range get some mutual 

 protection from the flies by congregating so that switching of 

 tails will brush their shoulders and heads. As previously men- 

 tioned, however, injuries result from kicking and hooking. Shade 

 of trees, shade of buildings, and open sheds offer very little pro- 

 tection. It is a common observation, however, that Tabanus phae- 

 nops does not follow animals into the higher and drier arid lands. 

 Stock in open range get much relief by going to sagebrush areas 

 during the heat of the day. 



67887°— 24 3 



