1^07.] White-grttbs and May- beetles. 



469 



insects were abundant in the beetle stage, making, indeed, the greater 

 part of the insect food of all the crows collected at that time. 



To these well-known facts I have to add two significant items of 

 observation reported to me by my field assistants. One of these, 

 Mr. E. O. G. Kelly, who was engaged during much of the season 

 of 1906 in a field study of injuries by white-grubs, unusually serious 

 that year in central Illinois, tells me that 'he often saw considerable 

 numbers of crows following after the plow in fall, evidently picking 

 up white-grubs, and that he has also seen flocks of! crows alight in 

 a .badly infested pasture and tear the sod in pieces in search of the 

 grubs, fighting with each other for their possession when thus ex- 

 posed. Another assistant, Mr. A. O. Gross, employed last fall in 

 collecting data for a census of the bird life of Illinois, found, in a 

 trip across the state made on foot in September and October, that, 

 next to the horned lark, crows were the most abundant birds on 

 plowed ground, averaging seventy-nine per square mile in all the 

 recently plowed fields crossed on that trip. They could have had no 

 other object there than the search for insect food.* 



In a study of the food of blackbirds, made by Mr. F. E. L. Beal 

 for the U. S. Department of Agriculture in 1894, it was found that 

 these birds ate either beetles or grubs in every month from March 

 to October inclusive. In May these insects made more than a sixth, 

 and in June one ninth, of the entire food. Many stomachs were 

 found to be literally crammed with grubs ; and in many more, grubs 

 had formed a large part of the previous meal. 



The Common Grub Wasp (Tiphia). — Much the most important 

 insect enemy of the white-grubs is a wasplike insect belonging to the 

 hymenopterous genus Tiphia. It is a slender, jet-black species, usu- 

 ally about two thirds of an inch long, but sometimes smaller, and 

 with wings either clear or more or less deeply tinged with dusky 

 yellow. It enters the ground in search of the grubs, follows them 

 up in their burrows, and lays on the back of each grub a single egg, 

 which hatches in a little over a week into a footless, maggot-like 

 larva. This larva adheres to the surface of the insect, punctures its 

 skin and sucks its blood for a time, but finally eats it up. The Tiphia 

 larva then spins, under ground, an oval brown coccoon within which 

 it goes through its transformations, coming out as a winged insect 

 the following summer. The rate of multiplication of the species 

 is not known, but it is certainly sufficient to enable the Tiphia vir- 

 tually to destroy, under favorable circumstances, the entire grub 

 population of a badly infested field. 



I _ • *"An Ortiithologrical Cross-section of Illinois in Aulnmn." By S. A. Forbes. Bull. 111. 

 State Lab. Nat. Hist., Vol. VII., Art. IX., p. 318. 



