DIPTERA. 439 



molts changes into a club-shaped pupa, the head and thorax 

 being greatly enlarged (514, b). With this transformation a 

 remarkable change takes place in the respi- 

 ratory system. There are now two breath- 

 ing-tubes, and these are borne by the 

 thorax. One of these tubes is represented 

 greatly enlarged by Figure 5 1 5, £. At the 

 tail-end of the body there is a pair of leaf- 

 like appendages, with which the insect breathing-tube of larva: 



rir & ' b, breathing-tube of 



swims ; for the pupae of. mosquitoes, and P u P a - 

 also of certain midges, differ from the pupae of other insects 

 in being active. The pupa state lasts only a few days ; then 

 the skin splits down the back, and the winged mosquito 

 carefully works itself out and cautiously balances itself on 

 the cast skin, using it as a raft, until its wings are hardened 

 so that it can fly away. 



The larvae of mosquitoes are doubtless beneficial insects, 

 for they feed on decaying matter in water, and thus act as 

 scavengers ; but the annoyance caused by the bites of the 

 adult females more than counterbalances this good. The 

 males of mosquitoes neither sing nor suck blood ; * they 

 are said to feed on the sweets of flowers. 



These pests can be repelled by smoke and by certain 

 strong-smelling substances. In regions where they abound 

 it is customary to build smudges in the evening for this 

 purpose ; and sportsmen anoint their faces and hands with 

 aromatic ointments. The best of these is made of mutton 

 tallow scented with camphor and oil of pennyroyal; a mix- 

 ture of oil of tar and oil of pennyroyal is also used. 



It often happens that plagues of these pests are bred in 

 receptacles of rain-water standing near dwellings; such re- 

 ceptacles should not be left open unnecessarily. When the 

 breeding-places are ponds of limited extent the larvae and 



*E. Ficalbi states that he has observed two Italian species in which both 

 sexes suck blood. Bull. Soc. Ent. Ital. 1889, p. 25. 



