ACTIVE GLEANERS 
127 
his perpetual energy and the occasional hurried call, 
given out without pausing in his work. 
The insect world may hold itself in check by the 
parasitism that besets every species. Perpetual 
warfare holds, controls, and restrains a possibility 
of reproduction sufficient to devour the world's 
vegetation. The balance of contending forces has 
swayed but little during the comparatively brief 
period covered by human observation ; and a lasy 
summer hour watching the ceaseless activity of the 
birds reveals their important part in the struggle 
that holds insect life in check. They are indis- 
criminate, it is true, feeding as freely on the useful 
parasite as on the injurious leaf-eater ; but they 
are an established element in the perpetual conflict, 
and cannot be destroyed or removed without grave 
danger. 
Birds destroy insect life in all its forms. Nowhere 
are the insects safe. Woodcock, Snipe, and other 
shore birds bore for them in the mud and sand. 
Robins pluck them from the hard earth. Thrushes 
turn over the leaves in search of them, Woodpeckers 
bore into the trees for them. They are caught on the 
wing by Kingbirds, Phcebes, Night-hawks, Swallows, 
and even Warblers and Sparrows. Nuthatches and 
Creepers search every crevice in the bark for them. 
The nimble little Warblers go swiftly and patiently 
over every branch, twig, and leaf, as if determined 
