14 



THE RELATION OF SPAEROWS TO AGRICULTURE. 



y.i 



IN' 



Fig. 8. —Eyes of 

 spider. 



broken off from the body, and is sometimes all that is left to show 

 that a click-beetle has been eaten. The pitted, earthenware-like wing- 

 covers of weevils (see PL II, fig. 7) and the curved, sharp jaws of 

 ground-beetle larvae are easily recognizable (see PL II, fig. 7). The 

 identification of Hymenoptera is much more difficult, as the distin- 

 guishing features are found mostly in the veining of the delicate 

 wings, which are exceedingly perishable. Ants, however, can always 

 be recognized hy the very hard jaws even when the action of the 

 stomach has practically reduced the insect to dust (see PL II, fig. 9). 

 Certain black wasps {Tiphid inoriiata) often eaten by birds may 

 be recognized in the stomach by the presence of a 

 tiny piece of the crust of the insect's back (meso- 

 thorax), which is sculptured by three parallel raised 

 ridges (see PL II, fig. 10). The presence of female 

 May-fiies can usuall}^ be detected by means of the 

 prettily reticulated eggs from within the insect's body 

 and the golden globule of oil each contains (see PL II, 

 fig. 11). Bugs (Ileteroptera) may be determined hy 

 their back shields (scutella), which are marked with dark dots and in 

 shape closely resemble equilateral triangles (see PL II, fig. 12); spi- 

 ders b}^ their jaws, which look like miniature cow horns, and their 

 minute eyes, which resemble clusters of gleaming gems (see fig. 8). 

 The remains of earthworms are identified with the compound micro- 

 scope, the high-power lenses of which reveal the characteristic 

 amber-colored S-shaped spicules (see fig. 9) with which the bodies 

 of the worms are beset. These lenses are also employed in identify- 

 ing bits of the skin of fruits and pastj^ masses of the endosperm, 

 or meat}^ part, of seeds. Differences can thus be ijerceived in the 

 structure of the epidermis of many fruits (see PL III, figs. 4 and 5) and 

 the starch grains of common cereals (see PL III, figs. 1, 

 2, and 3). When a bird has eaten poison ivy there often 

 remains nothing of the fruit except certain black, club- 

 shaped bodies (see PL III, fig. 6) which coat the stone 

 below the white skin of the fruit. The stones of bay- 

 berries are similarly covered with small granules (see 

 PL III, figs. 7 and 8), which furnish the clew in each 

 case when the stones are absent. 



After each element in a bird's stomach has been identified and 

 placed in a separate pile, the percentages of the different elements 

 are estimated by volume.^ In recording the results of examinations 

 a separate record is made for each species and for each month. 

 Monthly averages are based on the number of stomachs collected in 



' Of course it must be understood that mathematical exactness is not attainable 

 in these examinations; but every possible means is taken to reduce the error to a 

 minimum, and with a sufficient number of stomachs a very correct idea may be 

 obtained of the proportions of the different elements of the food. 



1 



Fig. 9.— Spicule 

 of earthworm. 



