452 STATE POMOLOGICAL SOCIETY. 



system of checks and balances to keep its species within proper bounds; and if 

 the argument be made of general application, it excludes the whole series of 

 insectivorous birds from any normal or useful part in the economy of nature. 



It would also be an interesting inquiry respecting the different classes of 

 agents for keeping insects in check, namely, the insectivorous birds, the pre- 

 daceous insects, and the parasitic insects, whether they occuj^y, to any consid- 

 erable extent, different and distinct fields of operation, and whetlier, therefore, 

 the work of one class may be said to be the complement of that of the others. 

 That this is true to a certain extent there can be no doubt, but to how great 

 an extent, it would require much time and investigation to determine. The 

 following statements may help to elucidate the subject. 



Birds seem to be the natural antagonists of such insects as are exposed to 

 view, or which are but slightly concealed, whilst those which are deeply hid- 

 den in the trunks of trees, in fruits, in the earth, or in the water, for the most 

 part escape them. But it is important to bear in mind that what may be 

 called exposed insects, embraces not only the superficial larva, such as the 

 leaf-eating and the leaf-rolling caterpillars, but it includes almost all kinds of 

 insects in their perfect or winged state. The crops of small birds are often 

 found to contain fragments of the hard wing-covers and legs of beetles. Those 

 birds which spend most of their time on the wing, like the night-hawks, must 

 depend almost wholly upon winged insects for subsistence. Swallows are 

 often seen skimming over the surface of ponds in search for the newly emerged 

 aquatic Neuroptera. And the fly-catchers capture most of their prey upon 

 the wing. On the contrary, we know that insects in their perfect or imago- 

 state are rarely attacked by either predaceous or parasitic insects. They are 

 either too hard to be injured by them, or too active to be caught by them. It 

 is therefore in their larva state that insects are so extensively destroyed by the 

 predaceous and parasitic species of their own class. But like all general rules 

 this has its exceptions. A few of the larger and more active carnivorous 

 insects, such as the dragon-flies, capture their prey on the wing, in a manner 

 very similar to that of the fly-catching birds. A few cases, also, are on record 

 of the parasitic ichneumon-flies being known to emerge from the bodies of 

 mature beetles. (Westwood, II., pp. 142-3). But these instances are so rare 

 that it is reasonable to suppose that the parasites did not attack the adult 

 insects, but that they deposited their eggs in the bodies of their larvaB, but at 

 so late a period that they did not come to maturity till after their foster-par- 

 ents had passed through their transformations. 



But this exemption of images from parasites does not seem to include those 

 outside of the hymenopterous order. The larvse of the parasitic beetles 

 (Meloe, Sitaris, Ripiphorns, and tStylops), are found in the bodies of adult 

 bees and wasps; and many of the two-winged Tachinse are known to deposit 

 their eggs upon the bodies of beetles. Many persons are familiar with the 

 eggs of these flies on the backs of potato beetles. 



Mr. Geo. M. Dodge, of Bureau county, wrote to me in 1872 : " More than half 

 of the Colorado potato beetles that I have found on our potatoes tliis fall have 

 had the eggs of some kind of Tachina on their wing covers, sometimes as 

 many as seven or eight on one beetle." Mr. Dodge also found similar eggs on 

 the Li/tta marginata, one of the blistering beetles which are injurious to pota- 

 toes. A European author, Leon Dufour, has described a species of Tachina 

 "which he reared from the larva state, and which he found in one of the Tor-^ 

 toise beetles; and another which he reared from one of the bugs proper,. 



