COLOUR-PRODUCING INSECTS. 63 



As grease exists in the vegetable as well as in the 

 animal world, it was an interesting question to know 

 whether animals derived their fat wholly from vege- 

 tables, or whether this substance could be formed in 

 the animal body. The vegetable tumours in which 

 the larvas of the Cynips are found contain no grease 

 or oily matter, whilst the grub that grows in them 

 is remarkably fat ! It is evident, therefore, that 

 animals have the power of forming fat or grease by 

 means of the starch or other principles supplied by 

 vegetables.* The conditions under which fat is 

 most readily formed are indeed those in which the 

 larvae of the cynips live, namely, a vegetable or 

 farinaceous diet, repose, solitude, and obscurity. 



It is not improbable that other insects besides 

 kermes, coccus, and cynips may become important 

 as dye-producers. Reaumur has spoken of an aphis 

 which produces galls in different parts of Asia, and 

 these galls are employed to dye silk a crimson colour. 

 Linnaeus also speaks of the tinctorial properties of 

 Aphis pini, an insect common in our climate, and 

 which produces a sort of gall-nut at the extremities 

 of the spruce fir. When these galls have attained 

 their maturity, says he, they burst and discharge a 



* Dumas and Milne Edwards formerly arrived at the same 

 conclusion. They fed bees exclusively upon honey and sugar, and 

 found that they produced wax y an observation which Huber had 

 already made many years before. 



