BIOLOGY AND HABITS OF HORSE FLIES 237 



The larval stage of most species is passed in the ground, and a 

 certain degree of moisture is necessary for proper growth and develop- 

 ment. Most species require very wet, or saturated soil, others are able 

 to develop in moderately moist earth. 



EGGS AND EGG LAYING 



The eggs are deposited by the female fly in clumps of several hundred 

 each, on vegetation, rocks, or other objects overhanging suitable places 

 for development of the larvas. When the eggs hatch, the young larvae 

 drop to the soil or water beneath and disappear from sight. Here they 

 remain for several months, sometimes for one or two years, when, after 

 passing through a short pupal period, they emerge as adult ffies. 



In some cases the "egg mass as well as the place of oviposition is 

 characteristic of the species, and renders identification easy, once the 

 observer sees one of which he knows the identity. 



In the Sierra Nevada Mountains of Eastern California where I havd 

 been studying tabanids for the past two years, the egg masses of the two 

 most important species are very easily distinguished. The egg mass of 

 Tahanus pwnctifer Osten Sacken is oblong, somewhat pyramidal in shape, 

 and about the size of the end of a man's little finger (plate XX, fig. 1). 

 It is usually deposited upon a buUrush or coarse grass stem, and from 

 one to three feet above the surface of the soil or water. When deposited, 

 as is the case with all horse fly eggs, the mass is milk white. In a day or 

 so, however, the color darkens to a mottled gray and white. Eggs of this 

 species are found most abundantly along lake shores. The egg mass of 

 Tahanus phaenops Osten Sacken is to be found on grass blades, three 

 or four inches above the soil in swampy places in meadows. This mass is 

 considerably smaller than that of Tahanus punctifer, is elongate, and 

 usually contains but two layers of eggs, while the other species usually 

 has about five layers. The egg mass of T. phaenops is black a day or 

 two after oviposition. This mass is inconspicuous and extremely hard to 

 locate in nature. 



In the Egyptian Sudan, Harold King found the eggs of Tahanus 

 kmgi Austen deposited in rounded masses on rocks rising from the edge 

 of a stream, generally overhanging the water, and from 6 inches to 15 

 inches above the water level. He also found the masses of Tahanus 

 ditaeniatus Macquart on grass growing in rain pools. The shape of the 

 egg mass of this species was variable, — some being long and narrow, 

 others short and broad. The same worker secured ovipositions of 

 Tahanus par Walker in a cage, on the under sides of leaves of a water 

 weed growing in a vessel of water. He also secured the egg masses of 

 Tahanus taeniola Palisot de Beauvois, the tabanid most frequently 



