244 SANITARY ENTOMOLOGY 



Mitzmain found the minimum life cycle of Tabanus striatus in the 

 Philippines to be 52 days. 



The life cycle of Tabanus lasiophthalmus was found by Hine in one 

 instance to be about 9 months. He states that the cycle of Tabanus 

 stygius probably requires two years. 



As has already been indicated in discussing larval periods, it is 

 probable that the species of Tabanus in the Sierra Nevada Mountains 

 require two seasons for their life cycles. 



HABITS OF ADULTS 



Only female adult horse flies attack stock (plate XIX). The males 

 are never found taking any interest whatever in warm-blooded animals. 

 Their food consists of the nectar of flowers and other sweet substances. 

 Females also feed readily on sweet substances. I have quite often cap- 

 tured a few in a fly trap baited with banana. It appears that the primary 

 object of the blood meal is to enable the female to develop eggs, although 

 this diet may also be taken for nourishment. 



The males are usually to be found in the grass, or the foliage of trees,. 

 or on the trunks of trees, and when the females are not sucking blood 

 they will usually be found in the same situations. 



In temperate climates females are most active on still, sunshiny days. 

 It is unusual to find them flying on cloudy days or when strong wind is 

 blowing. 



In taking a meal of blood a female Tabanus will usually insert and 

 withdraw the beak several times, puncturing the skin of the host in a 

 new place each time, before finishing the meal. The length of time 

 occupied in taking a meal in cases observed by the writer has varied from 

 about 3 to 11 minutes, and during this time the position may be changed 

 5 or 6 times. Mitzmain has seen Tabanus striatus in the Philippines feed 

 for 23 minutes. I have allowed flies to bite my arm and feed to satiety. 

 It is not a continuously painful process. The only part of the per- 

 formance that is painful is the insertion of the beak, which takes but a 

 few seconds. After that the drawing of the blood by the fly causes no 

 sensation whatever in the arm. However, the habit of changing position 

 so often during a meal is somewhat annoying. 



Horses are much more nervous under the attacks of Tabanus than 

 cows. The latter often allow the flies to feed without much of any 

 attempt to brush them off^, but a horse fights constantly. Where the 

 attack is severe, the horses in a pasture will bunch up together for 

 mutual protection in rubbing against each other. Under such conditions 

 it is possible that each fly will attack several horses, being brushed off' 

 several times before the meal is finished. This makes an ideal condition 



