395 THE PHILOSOPHY" ' .-l 



a pair of fparrows, during the time they have their youtig to feed, 

 deftroy, every week, 3360 caterpillars. This calculation he founded 

 upon adual obfervation. He difcovered that the two parents car- 

 ried to the neft 40 caterpillars in an hour. He then fuppofes, which 

 is a moderate fuppofition, that the fparrows enter the neft only 12 

 hours each day, which is a daily confumption of 480 caterpillars. 

 This fum, multiplied by 7, or the days of a week, gives 3360 cater- 

 pillars extirpated weekly from a garden. The utility of thefe birds 

 is not limited to this circumftance alone; for they likewife feed their 

 young with butterflies, and other winged infers, each of which, if 

 not deftroyed in this manner, would be the parent of feveral hun- 

 dreds of caterpillars. Thofe butterflies and caterpillars which are 

 covered with hair are rejedted by fome birds, who prefer flies of a 

 fmoother and fmaller kind. But thefe hairy fpecies, it ftiould be con- 

 fidered, are the food of the worms which are transformed into thofe 

 fmaller flies that afford nourifhment to the birds which rejedl the 

 hairy caterpillars and butterflies, 



Shell-fiflies are extremely prolific, and fo ftrongly fortified by Na- 

 ture, that their increafe, one flaould imagine, would foon augment to 

 a degree that might be hurtful to other fpecies. Their noxious mul- 

 tiplication, however, is checked by numberlefs enemies. But their 

 moft deftrudive enemy is the trochus, which is a kind of fea-fnail. 

 This animal is furniflied with a ftrong, mufcular, hollow trunk, bor- 

 dered at the extremity with a cartilage toothed like a faw. Againft 

 this inftrument, which adls like an augre, no {hell, however hard or 

 thick, is a fufficient defence. Thefe animals, called trochi, fix them- 

 felves upon an oyfter or a mufcle, bore through the fhell with their 

 trunk, and devour their prey at their leifure. The animal attacked, 

 if a bivalve, may open or fhut its (hell ; but no efforts of this kind 

 can be of any avail ; for the trochus remains immoveably fixed till 

 it has completely fucked out the vitals of its prey. In this cruel oc- 

 cupation 



