44 BRITISH INSECTS 



morphosis is incomplete, it is not accomplished with- 

 out a break in the creature's activity. In the stage 

 before the final change the nymph becomes sluggish 

 (in some species inert) and takes no food. Its body, 

 limbs, and wing-rudiments are enveloped in a thin skin, 

 which is cast off prior to the assumption of the adult 

 state. Thus, as Professor Carpenter has remarked, 

 " the development of the Thysanoptera exhibits an 

 interesting transition towards a true metamorphosis." 1 



About fifty species of thrips have been found in 

 Britain. Most, if not all, of them suck the juices of 

 plants, attacking chiefly the essential organs of flowers. 

 In this way considerable damage is often done to 

 cultivated crops. The pea and bean thrips, 2 known to 

 farmers as the " black fly," is the subject of a leaflet 

 issued by the Board of Agriculture and Fisheries. 

 Another species 3 is harmful to wheat and other cereals. 



Members of the ninth order of insects (the Hemi- 

 ptera) have their mouth-parts definitely modified for 

 piercing and sucking. The mandibles and first 

 maxillae are transformed into long, slender stylets, 

 which work to and fro within a kind of grooved sheath 

 (called the rostrum) which is formed by the union of 

 the second maxillae. The whole contrivance consti- 

 tutes a lengthy proboscis, which, when not in use, lies 

 directed backwards beneath the body. When one of 

 the Hemiptera feeds, it first brings the tip of its rostrum 

 into contact with the organism (plant or animal as the 

 case may be) that it is about to attack. The sharp- 

 pointed stylets are then driven into the tissues, and a 

 stream of saliva is pumped down the rostrum into the 

 wound. The saliva is believed to arrest coagulation of 



1 " Insects, their Structure and Life." 



2 Thrips pisivora. 3 Thrips cerealium. 



