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SCIENCE. 



[Vol. XIV. No. 354 



morning (prior to 7 A.M.) showed very few eggs, not more than 

 eight or ten to a single dropping, while that dropped between 4 

 P.M. and later in the night contained still fewer. . On a dung 

 dropped between 10 and 11.30 a.m. in the hot sunshine, however, 

 examination a few minutes after showed a large number of eggs, 

 estimated at three hundred and fifty. Other very fresh droppings 

 were examined, and the eggs were found to range from none at all 

 to over three hundred. One animal was then fortunately observed, 

 from close quarters, in the act of passing her dung. As the opera- 

 tion commenced, forty or fifty of the flies moved from the flank to 

 the back of the thigh, near the " milk mirror ; " and at the close of 

 the operation they were seen to dart instantly to the dung, and to 

 move quickly over its surface, stopping but an instant to deposit an 

 egg. The abdomen and ovipositor were fully extended, and the 

 wings were held in a resting position. Most of them had left the 

 dung at the expiration of thirty seconds, while a few still remained 

 at the expiration of a minute. Every individual had returned to 

 the cow, however, in little more than a minute. This explains the 

 previous non-success in observing the act of oviposition ; for the 

 Virginia cattle on the large stock-farms are comparatively wild, and, 

 although the dung was examined as speedily as possible after 

 dropping, the flies had already left. 



The results, therefore, indicate that the eggs are deposited dur- 

 ing daylight, chiefly during the warmer time of the day, between 9 

 and 4, and mainly between 9 in the morning and noon. They are 

 laid singly, and never in clusters, and usually on their sides on the 

 surface of the wet dung, seldom inserted in cracks. 



After the eggs hatch, the larva descend into the dung, remain- 

 ing, however, rather near the surface. When ready to transform, 

 the larvae evidently descend from the dung into the ground below 

 from a half to three-quarters of an inch. Actual observations were 

 made on larvse in dung in breeding-cages where the soil was fine 

 sand, affording ready entrance to the larva. Where the dung has 

 been dropped upon hard ground, the probabilities are that they 

 will not enter so deeply, and may indeed transform upon the sur- 

 face of the ground at the bottom of the dung. 



From the records it appears that from ten to seventeen days, say 

 two weeks, is about the average time from the laying of the egg to 

 the appearance of the flies ; and with four active breeding months, 

 from May 15 to Sept. 15, there will be eight generations. The flies 

 will undoubtedly breed later than Sept. 15, but this time may be 

 allowed to make up for the time occupied in the development of the 

 eggs in the abdomen of the female. With seven or eight annual 

 generations, the numbers of the flies are not surprising. 



The flies were observed in the greatest abundance during July. 

 They make their first noticeable appearance in Virginia early in 

 May, and, from hearsay evidence, remain until " late in the fall " or 

 until " right cold weather." Sept. 28, they were still as abundant 

 as ever around Washington. The characteristic habit of cluster- 

 ing about the base of the horn seems to exist only when the flies 

 are quite abundant. When they average only a hundred or so to a 

 single animal, comparatively few will be found on the horns. 

 Moreover, as a general thing, the horn-clustering habit seems to be 

 more predominant earlier in the season than later, although the 

 flies may seem to be nearly as numerous. The clustering upon the 

 horns, although it has excited considerable alarm, is not productive 

 of the slightest harm to the animal. Careful study of the insects 

 in the field show that they assume two characteristic positions, — 

 one while feeding, and the other while resting. It is the resting 

 position in which they are always found when upon the horns. In 

 this position the wings are held nearly flat down the back, over- 

 lapping at the base, and diverging only moderately at the tip. The 

 beak is held in a nearly horizontal position, and the legs are not 

 widely spread. In the active sucking position, however, the wings 

 are slightly elevated, and are held out from the body, not at right 

 angles, but approaching it, — approximately an angle of sixty de- 

 grees from the abdomen. The legs are spread out widely ; and 

 the beak, inserted beneath the skin of the animal, is held in nearly 

 a perpendicular position. The fly, before inserting its beak, has 

 worked its way through the hairs close to the skin. While feed- 

 ing, however, the hairs which can be seen over its body do not seem 

 to interfere with its speedy flight when alarmed ; for at a fling of 

 the tail, or an impatient turn of the head, the flies rise instantly in 



a cloud for a foot or two, returning again as quickly, and resum- 

 ing their former positions. 



The horns are not the only resting-places ; for, with the horns 

 black for two inches above their baise, we have seen the flies 

 towards nightfall settle in vast numbers upon the back between 

 the head and fore-shoulders, where they can be reached by neither 

 tail nor head. When feeding, they are found over the back and 

 flanks, and on the legs. During a rain-storm they flock beneath 

 the belly. When the animal is lying down, a favorite place of 

 attack seems to be under the thigh and back belly, around the bag. 

 With certain animals the dewlap seems to be badly attacked, while 

 with others this portion of the body is about exempt. Certain 

 cattle, again, will be covered with flies, and will lose condition 

 rapidly, while others are but slightly troubled. 



On the horns the flies settle thickly near the base, often forming 

 a complete band for a distance of two inches or more. They seem 

 to prefer the concave side to the convex side of the curve of the 

 horn, probably for the reason that the cow cannot scrape them off 

 so readily ; and one cow was noticed in which they reached nearly 

 to the tip of the horn on the concave side of the curve only. 



The amount of damage done by the fly has been exaggerated by 

 some, and underestimated by others. Many rumors have been 

 heard of the death of animals from its attacks, but not a single 

 case as yet has been substantiated. It is believed that the flies 

 alone will never cause the death of an animal. They reduce the 

 condition of stock to a considerable extent, and in the case of milch 

 cows the yield of milk is reduced from one-fourth to one- half. 

 Their bites seldom even produce sores by themselves, although a 

 number of cases have been seen where large sores had been made 

 by the cattle rubbing themselves against trees and fences in an 

 endeavor to allay the irritation caused by the bites ; or, in spots 

 where they could not rub, by licking constantly with the tongue, 

 as about the bag and on the inside of the hind-thighs. A sore 

 once started in this way will increase with the continued irritation 

 by the flies, and will be difficult to heal. Those who underesti- 

 mate the damage believe that the flies do not suck blood ; but such 

 persons have doubtless watched the flies only upon the horns or 

 elsewhere in their resting position, when the beak is not inserted, 

 or have caught them and crushed them when their bodies con- 

 tained little blood. In reality, the flies suck a considerable amount 

 of blood, however, and it is their only nourishment. If captured 

 and crushed at the right time, the most sceptical individual will be 

 convinced. 



■ Almost any greasy substance will keep the flies away for several 

 days. A number of experiments were tried in the field, with the 

 result that train-oil alone, and train-oil with a little sulphur or 

 carbolic acid added, will keep the flies away for from five to six 

 days, while with a small proportion of carbolic acid it will have a 

 healing effect upon sores which may have formed. Train-oil 

 should not cost more than from fifty to seventy- five cents per 

 gallon, and a gallon will anoint a number of animals. Common 

 axle-grease, costing ten cents per box, will answer nearly as well ; 

 and this substance has been extensively and successfully used by 

 Mr. William Johnson, a large stock-dealer at Warrenton, Va. 

 Tallow has also been used to good advantage. The practice of 

 smearing the horns with pine or coal-tar simply repels them from 

 these parts. Train-oil or fish-oil seems to be more lasting in its 

 effects than any other of the substances used. 



A great deal has been said during the summer concerning the 

 merits of a proprietary substance, consisting mainly of tobacco- 

 dust and creosote, known as "X. O. dust," and manufactured by a 

 Baltimore firm, as an application to cattle : and it has received an 

 indorsement from Professor J. B. Smith, entomologist to the New 

 Jersey Experiment Station. This substance has considerable 

 merit as an insecticide, and will kill many of the flies when it 

 touches them, although they die slowly, and a few may recover. 

 The substance costs twenty-five cents per pound, and is not last- 

 ing in its effects. Where it is dusted through the hair, the flies, on 

 alighting, will not remain long enough to bite ; but two days later 

 they are again present in as great numbers as before. A spray of 

 kerosene emulsion directed upon a cow would kill the flies quite as 

 surely, and would be cheaper ; but it is not advisable to attempt to 

 reduce the numbers of the pest by actually killing the flies. 



