334 A BOOK OF INSECTS 



tiie air ; also as an external medical application in various 

 ailments. The curiosities known as " ground pearls " are 

 the outer shells of coccids which belong to the genus 

 Margarodes. In South Africa, and the island of St. 

 Vincent, they are collected and strung together as neck- 

 laces and bangles which are sold to tourists. 



By far the most important products of scale insects, 

 however, are lac and cochineal. Lac is secreted in large 

 quantities by Carteria lacca upon the twigs of its food 

 plants — fig, buckthorn, and other trees. It is imported 

 from India in its natural state, and after treatment forms 

 the basis of varnish, French polish and many other im- 

 portant materials. The bodies of the female lac insects 

 also yield the crimson pigment known as "lake"; but 

 the chief dye-producing coccid is Coccus cacti, the cochineal 

 insect. A native of Mexico, it was long ago carried 

 by man to the Eastern Hemisphere, and became thoroughly 

 acclimatised in the Canary Islands. Cochineal, w r hich in 

 its crude form consists of the dried female coccids, has 

 been largely displaced in commerce by aniline dyes ; but 

 it is still employed almost exclusively for colouring sweet- 

 meats and confectionary, and in pharmacy. Other species 

 of scale insects yield a crimson dye, and some of these 

 have been known to man from the earliest times. 



We see, therefore, that mankind is affected by the 

 activities of insects in a great variety of ways. We can 

 point decisively to many foes and many friends, but there 

 are myriads of insects whose status remains obscure. 

 Whether their influence is baneful or beneficial remains 

 to be discovered. Thus, while the study of insects is 

 interesting for its own sake, its chief justification consists 

 in its bearing upon human affairs. This book may be 

 fittingly concluded by an extract from the writings of 

 Dr. S. A. Forbes. " The life-histories of insects lie at 



