DIRECT BENEFITS DERIVED FROM INSECTS. 191 
stronger that twenty threads will carry an ounce more.* Don Luis Neé 
observed on Psidium pomiferum and pyriferum ovate nests of caterpillars 
eight inches long, of grey silk, which the inhabitants of Chilpancingo, 
Tixtala, &ec., in America, manufacture into stockings and handkerchiefs.? 
Great numbers of similar nests of a dense tissue, resembling Chinese 
paper, of a brilliant whiteness, and formed of distinct and separable layers, 
the interior being the thinnest and extraordinarily transparent, were ob- 
served by Humboldt in the provinces of Mechoacan and ‘the mountains of 
Santarosa, at a height of 10,500 feet above the level of the sea, upoi the 
Arbutus Madréno, and other trees. The silk of these nests, which are the 
work of the social caterpillars of a Bombyx (2. Madréno), was an object 
of commerce even in the time of Montezuma ; and the ancient Mexicans 
pasted together the interior layers, which may be written upon without 
preparation, to form a white glossy pasteboard. Handkerchiefs are still 
manufactured of it in the Intendency of Oaxaca, De Azara states that 
in Paraguay, a spider, which is found to near the thirtieth degree of 
latitude, forms a spherical cocoon (for its eggs) an inch in diameter, of a 
yellow silk, which the inhabitants spin on account of the permanency of 
the colour.t And according to M. B. de Loziéres, large quantities of a 
very beautiful silk, of dazzling whiteness, may be collected from the 
cocoons even of the Ichneumons that destroy the larvae of some moth in 
the West Indies, which feed upon the indigo and cassada.° 
It is probable, too, that other articles besides silk might be obtained 
from the larvae which usually produce it, particularly cements and varnishes 
of different kinds, some hard, others elastic, from their gum and silk 
reservoirs, from which it is said the Chinese procure a fine varnish, and 
fabricate what is called by anglers Indian grass.° The diminutive size of 
the animal will be thought no objection, when we recollect that the very 
small quantity of purple dye afforded by the Purpura of the ancients did 
not prevent them from collecting it. 
I now conclude this long series of letters on the injuries caused b: 
insects to man, and the benefits which he derives from them ; and I think 
you will readily admit that I have sufficiently made good my position, that 
the study of agents which perform such important functions in the eco- 
nomy of nature must be worthy of attention, Our subsequent corre- 
spondence will be devoted to the most interesting traits in their history — 
as their affection to their young, their food and modes of procuring it, 
habitations, societies, &c. 
Tam, &e. 
1 Pullein in Phil. Trans. 1759. 54, 
2 Annals of Botany, ii. 104. 
5 Political’ Essay on N. Spain, iii. 59. 
+ Voyage dans ’ Amer. Mérid. i. 212. Tt may here be observed as a benefit 
derived by the higher walks of philosophy from insects, that astronomers employ 
the strongest thread of spiders, the one namely that supports the web, for the divi- 
Slons of the micrometer. By its ductility this thread acquires about a fifth of its 
ordinary length. Wouv. Dict. d’Hist. Nat. ii, 280. 
5 American Phil. Trans. v. 826. 
5 Anderson’s Recreations in Agriculture, So. iy. 899, 
