AUGUST 143 



not harbour, though they may receive occasional visits 

 from, the species of gnat known as Anopheles which 

 disseminates Mediterranean fever, nor the deadly 

 Stegomyia calopus, the carrier of yellow fever. The 

 manner in which the last-named gnat has been brought 

 under control, and almost extirpated in Panama and 

 the West Indies, forms the subject at once of a 

 fascinating romance and one of the most brilliant 

 chapters in the history of applied science. 



There is no obscurity in the purpose with which the 

 insects briefly referred to above attack human beings. 

 They are out for blood. But my house of recent years 

 has been frequented in late summer by an insect 

 whereof the operations are involved in considerable 

 mystery. This is Ophion luteus, a fly half an inch 

 long, of a yellow hue, with the abdomen united with 

 the thorax by an extremely slender attachment, 

 resembling that feature in some of the solitary wasps. 

 It belongs to the family Ichneumonidce, whereof about 

 6000 species have been recognised, more than 1200 

 being indigenous to Great Britain. Every member of 

 this family is parasitic, the female of each species 

 depositing her eggs in or on the body of some in- 

 voluntary host, which is usually the larva of one of 

 the Lepidoptera or other flying insect. 1 Each species 

 of ichneumon-fly is parasitic on a special species, or at 

 least genus, of insect. The female deposits her eggs by 

 means of an ovipositor an instrument in some species 



1 Apanteles glomerate, the ichneumon-fly which is the parasite of 

 the common white butterfly, deposits its eggs in the eggs of the 

 butterfly and they are hatched in the body of the caterpillar, reside 

 and feed there, ultimately causing its death. 



