N. S. Bailey.
Field Notes on Tabanus nigrovittatus Macquart.
Psyche 54(1):62-64, 1947.

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FIELD NOTES ON TABANUS NIGRO-
ITITTATUS MACQUART1
BY X. S. BAILEY
Cambridge, Mass.
This horsefly was the subject of an intensive study that was started in mid-July, 1946, and was suspended only with the advent of winter. The fly might well be called the Saltmarsh Greenhead since its immature stages are evidently quite dependent 011 the conditions of the Spar- tka zones for their developnient. Wherever expansive salt marshes occur-from Nova Scotia to Texas-this insect is known and may become locally abundant. At such times it is extremely annoying to man and to do- mestic animals. Despite its general coastal distributioi~ and common occurrence, the literature records only meagre details of its life history or of its specific require- ments. This paper reports some initial results of the current investigation.
Abundance. Two incidents will serve to emphasize how abundant the species is at the height of its season. In Essex County, Massachusetts they appear about the first of July each year and are at their peak for the last three weeks of that month. Usually there is a marked decline in their numbers by early August. The decline is augmented when a northeast storm brings a spell of unseasonably cold, wet weather. The past suninier was typical in this respect.
My real introduction to this species came on the warm, sunny afternoon of July fifteenth. A call was made at the farm of Mr. Martin Burns on U. S. Route 1 in Sew- bury. He was found mowing a field that lies above and just south of the Parker River. Two sturdy grey horses 1 This investigation of the biology of I. nigrovittatus is being conducted for a joint board of the State Department of Public Health and the State Reclamation Board with a grant from the Massachusetts Legislature. I wish to acknowledge the generosity of Dr. Joseph C. Bequaert, Curator of Insects in the Museum of Comparative Zoology, who freely devoted his time to the determination of the Tabanidffi and liberally assisted me in many other ways. Tor the progress of this study I am greatly indebted to his friendly guidance.
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were hitched to the mowing machine.
Tabanids were
swarming' around the patient animals.
Practically all
were Tabanus nigrovittutus, although a few other types -notably T. atratus and C71rysops species-were ob- served. The team was flecked with blood from the fly bites. The clots showed plainly on their light coats and gave an indication of favored feeding areas. In order of decreasing frequency, the chest region, the head and neck, the median side of the upper legs, the flanks, and the belly received most attention from the flies. However, the Tabanids were all over them and allowed them no respite. They were experienced horses and maintained a remarkable calm considering the severity of the inces- sant attack.
It has long been known that such conspicuous objects as automobiles attract Tabanids. July eighteenth was another bright, warm day. After lunch the writer drove out Argilla Road towards Crane's Beach, Ipswich. Where the road crosses Fox Creek its bed is raised well above the marshes. The coup6 was parked just beyond the bridge while some observations were made. On re- turning to the car an astounding number of greenheads were noted in it. The thought of making a timed collec- tion suggested itself. The results are numerically em- phatic. They give graphic evidence of the abundance of the Saltmarsh Greenliead under favorable circumstances. In fifteen minutes actual collecting time a total of 475 flies were taken by simply lifting a half -pint bottle, containing some alcohol, under them when they alighted on the inner roof covering. The disturbance caused them to fly down- ward into the liquid which quickly dispatched them. This collecting, at the rate of more than thirty a minute, could unquestionably have been continued much longer without noticeably diminishing the supply.
Mating.
The mating of Tabanids is seldom observed. On one occasion only it was my privilege to find several pairs of T. nigrovittat us in copulation. At that time, un- fortunately, the rarity of such an event was not realized or more attention would have been given to details. The morning" of July twenty-fifth was very warm, humid, and



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64 Psyche [Mar.
hazy-bright.
There was still some fog lingering over the marsh at Conomo Point, Essex, when I arrived at nine- thirty. On approaching the Point, a sharp left turn was made over a small but abrupt rise from which the road falls quickly away to the tide line. The first cottage on the left was surrounded on three sides by salt marsh. There was a convenient place to park in front of it. Im- mediately after getting out on the marsh a continuous low buzzing sound was noted. Then swarms of greenheads were seen hovering just a few. inches above tlie dense cover of the fine marsh grass (Spurtma patens). On the far side of the cottage a slight depression was discovered where a small, sparse patch of the larger and coarser Spartina alterrtiflora stood. On the upper surface of the broader blades of these plants some mating pairs of greenheads were seen. One was resting on the back of the other with its head about over the mesothorax of the mate beneath. Although it was possible to approach the paired flies more closely than is usual with individuals, they remained alert and were not too easy to catch with the net. The carrier could still take off readily and fly rather well. If disturbed they would move to another plant two or three yards away while retaining their rela- tionship. Four or five pairs were caught there and they included the first males taken. Another stop was made at the same place on August sixth. In the thirty or forty minutes then spent on the marsh only five or six flies were seen. This time the owner of the cottage mentioned above was there. After explaining the purpose of the visit to him, Mr. Derby remarked that a carpenter lie had engaged to work on the building in a previous year had told him of the hum produced by the hovering flies. This volunteered information was of interest in the light of my own experi- ence. That spot is apparently a regular mating place for this species.




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