20 
The Ohio Naturalist. 
[Yol. VII, No. 2, 
densely wooded tract on rather low and level ground is often 
referred to as a swamp. Here these flies abound, and at times 
are so abundant that it is impossible to drive some horses into 
their domains. Other animals when compelled to withstand 
their attacks are difficult to control, for the bites are numerous 
and severe. It is hardly possible to describe their abundance 
properly, they must be seen to be appreciated fully. 
Although the different species are much alike in general 
appearance, they are quite easily separated when both sexes of 
all of them are at hand. Some have the eyes hairy, a character 
which is most conspicuous in the male; in the eyes of some of 
the males the factes are all nearly of the same size, in others 
there is a very small area of large factes on the disc of each eye, 
while in others the area of large facets is so extended that two- 
thirds of the extent of the eyes is included. Some of the species 
have the eyes pilose and here the difference in the extent of the 
area of large factes is as pronounced as in the other case. Where 
there are no large facets the head is smaller than in the cases 
where these are of large extent. Some species have a short 
stump of a vein near the base of the branch of the third longi¬ 
tudinal, and good specific characters exist in the coloration of the 
posterior femora. The last two characters seem rather trivial 
when used in reference to the members of the family in general, 
but I have found that in this group, when used in connection 
with the structure of the eyes of the male, they are very constant 
and consequents may be used with good results in separating 
the females. The banding of the eyes and the coloration of the 
thorax and abdomen are specific characters in some cases; also 
the relative size of the first antennal segment of the various 
species is of value, but as this last can be expressed only as a 
comparison with some other species its value in keys and 
descriptions is very limited. 
In some of the species the males have the habit of hovering 
in the sunshine as the Svrphid flies do. This habit was only 
observed bv mvself in two species, both belonging to the section 
with uniform sized facets. The first observation was made in 
reference to the species I have identified as Tabanus truquii, 
near Sanarate, Guatemala. While riding on horseback along 
the main road I saw the fly hovering about six or eight feet above 
the ground in bright sunshine. The specimen was accommo¬ 
dating enough to remain in the same place until I dismounted, 
got my net together and captured it. The other species I 
observed along the railroad near Puerto Barrios. I had been 
walking where the track was more or less shaded, but rather 
suddenlv coming out into an open place where the sun’s says 
were not obstructed, I could see dozens of Tabanids hovering 
just above my head and succeeded in capturing a number of 
