INDIRECT BENEFITS DERIVED FROM INSECTS. 201 



with the locusts, and then accompany them in astonishing numbers, prey- 

 ing upon them in their larva state. The common sparrow, though pro- 

 scribed as a most mischievous bird, destroys a vast number of insects. 

 Bradley has calculated that a single pair, having young to maintain, will 

 destroy 3360 caterpillars in a week.^ They also prey upon butterflies 

 and other winged insects. The fly-catchers (Muscicopa) , and the warblers 

 (Motacilla), which include our sweetest songsters, are almost entirely sup- 

 ported by insects ; so that were it not for these despised creatures we 

 should be deprived of some of our greatest pleasures, and half the interest 

 and delight of our vernal walks would be done away. Our groves would 

 no longer be vocal ; our little domestic favorites the red-breast and the 

 wren would desert us; and the heavens would be depopulated. We 

 should lose too some of the most esteemed dainties of our tables, one of 

 which, the wheat-ear, is said to be attracted to our downs by a particular 

 insect.^ Lastly, insects are the sole food of swallows, which are always 

 on the wing hawking for them, and their flight is regulated by that of 

 their prey. When the atmosphere is dry and clear, and their small game 

 flies high, they seek the skies; when moist, and the insects are low or 

 upon the ground, they descend, and just skim the surface of the earth and 

 waters ; and thus by their flight are regarded as prognosticating fair or wet 

 w^eather. I was one summer much interested and amused by observing 

 the tender care and assiduity with which an old swallow supplied her 

 young with this kind of food. My attention was called to a young brood 

 that, having left their nest before they were strong enough to take wing, 

 were stationed on the lead which covers a bow window in my house. 

 The mother was perpetually going and returning, putting an insect into 

 the mouth first of one then of the others in succession, all fluttering and 

 opening their mouths to receive her gift. She was scarcely ever more 

 than a minute away, and continued her excursions as long as we had time 

 to observe her. When the little ones were satisfied, they put their head 

 under their wing and went to sleep. The number of insects caught by 

 this tribe is inconceivable. But it is not in summer only that birds derive 

 their food from the insect tribes : even in winter the pupae of Lcpi- 

 doptera, as Mr. White tells us, are the grand support of those that have a 

 soft bill.^ 



I shall close my list of the Indirect benefits derived from insects, by ad- 

 verting to the very singular apparent subserviency of some of them to the 

 functions of certain vegetables. 



You well know that some plants are gifted with the faculty of catching 

 jiies. These vegetable Mascicapoi, which have been enumerated by 

 Dr. Barton of Philadelphia, who has published an ingenious paper on the 

 subject"*, may be divided into three classes : — First, those that entrap insects 

 by the irritability of their stamina, which close upon them when touched. 

 Under this head come Apocynum androsctmifolium, Asclepias syrica and 

 curassnvica, Nerium oleander, and a grass described by Michaux under the 

 name of Leersia lenticularis. The second class includes those which 

 entrap them by some viscosity of the plant, as many species of Rhododen- 



> Reaum. ii. 408. « Bingley, ii. 374. 



3 White's Selborne, i, 181. * Philos. Mag. xxxix. 107. 



