LEPIDOPTERA 



223 



venomous. Recently Bleyer has described caterpillars belonging 

 to the Bombycidae of Brazil which possess peculiar stinging organs, 

 the venom from which produces locally urticaria and dermatitis, as 

 well as general symptoms, which arc best treated by the local appli- 

 cation of a 2 per cent, solution of menthol in aether, chloroform, 

 and rectified spirits, and by the administration of a mixture con- 

 taining liquor ammonise acetatis. 



Porthesta Chrysorrhcea.— The caterpillar of this brown-tailed moth 

 is reported from America (Massachusetts and New Hampshire) as 

 causing a peculiar skin eruption, which Tyzzer says is caused by 

 the penetration into the epidermis of peculiarly modified micro- 

 scopic hairs called the nettling hairs, which are sharply pointed and 

 barbed. These hairs are specially arranged for penetration, and 

 possess an irritating substance which can be destroyed at 115° C. 

 The other hairs are innocuous. The poison causes necrosis of the 

 cells of the epidermis, together with the formation of small vesicles 

 and inflammation of the corium. 



The Symptoms, which are generally those of an urticarial der- 

 matitis, but occasionally erysipelatous-like, may be divided into 

 two groups: (i) severe, due to contact with the caterpillar; (2) mild, 

 due to hairs blown into the air and lodging in skin or under-gar- 

 ments. But it must be remembered that some people are very 

 sensitive and others almost immune. 



Treatment.^ — ^The best treatment is to clear away the hairs with 

 a little alkaline lotion (bicarbonate of soda 2 per cent.), and then 

 to apply an ointment of ichthyol (10 per cent.). 



5. Diptera. 



The classification of the Diptera is given in Chapter XXXII., p. 775, 

 to which reference should be made. 



CulicidcB. — The irritation ot mosquito-bites is most noticed by 

 the new-comer to the tropics, for as years go by a kind of partial 

 immunity is acquired, and the bites are much less noticed. Some 

 people appear to have a partial natural immunity to the bites, but 

 this is uncommon. 



Only the female mosquito bites and sucks blood, which is sup- 

 posed to be required for the nutrition of the eggs. When the 

 female mosquito alights upon the skin, it does not always bite at 

 once, but may move from one part to another, apparently testing 

 the different parts of the skin by its labellse.* 



Having selected a given area of skin, it moves the palpi away 

 from the proboscis dorsally, and at the same time rotates the 

 labellse on their hinge- joints outwards. 



The labium is now pressed against the skin, and is bent into the 

 form of a bow, convex posteriorly. An opening in the skin is then 

 made, in which the mandibles and maxillae work like saws, while 

 the head of the mosquito can be seen rocking from side to side. 



* For the anatomy of the proboscis see^Chapter XXXII., p. 776. 



