258 



NA TURA L HIS TOR Y. 



with the anterior part of the back upwards. At last the time for the 

 emergence of the perfect insect arrives. The pupa now rises to the sur- 

 face of the water, and at last floats upon it. The skin now splits down 

 the back, and from the opening thus formed the mosquito draws its body, 

 legs, and wings ; and then, standing upright in the old pupal case, as one 

 would in a boat or canoe, it allows the flabby wings to dry. This period is 

 fraught with great danger to the young mosquito, for the slightest wind 

 will upset the boat in which he stands, and an immersion in the water 

 will quickly result in the death of the delicate form. 



As is well known, summer and autumn are the seasons when these 

 insects most abound, and at times they occur in enormous swarms. At 

 other seasons of the year they may occur, and the writer once remembers 

 visiting a house which was inflicted with them in the month of February. 

 A little examination showed the cause. A number of hyacinth glasses 

 standing in the window formed the breeding-grounds, and in them wrig- 

 glers were to be seen in great numbers. The glasses were emptied, and 

 the plague ceased until the next season. 



The horse-flies are considerably different from the mosquitos, but tliey 



have one feature in common with them, — it is the 

 female which bites. They will fly round and round 

 a horse, with a dull, droning note, seeking some un- 

 protected spot on which to alight, and suck their fill 

 of blood. Their larvae, too, are carnivorous, and prey 

 upon insects and snails, thus partially repaying the 

 farmer for the torments they cause his live-stock. 



The robber-flies are also large, strong forms, which 

 do a considerable amount of good by their predaceous 

 habits. They fly strongly and quickly, resting on some bush or on the 

 ground until the}' see some insect, when they dart after it, grasp it with 



their strong feet, and run their beak through it. Our 

 figure shows a species which in this way does consid- 

 erable good by destroying injurious insects, while its 

 larva feeds upon the eggs of the western locust. 



The bot-flies, on the other hand, are to be regarded 

 as unmitigated nuisances, from their parasitical habits 

 in the preparatory stages. There are some sixty spe- 

 cies known, all of which prey upon the vertebrates, and 

 all but one upon mammals. • In the habits of the various species there are 

 considerable differences to be noted. 



First to be mentioned is the bot-fly of the horse, very familiar to all 

 who have much to do with these useful animals. It is a brownish species. 



Fig. 248. — Horse-fly 



harms). 



(To- 



Fig. 249. — Robber-fly 

 {Erax). 



