90 
PROMACHUS VERTEBRATUS Say 
This important enemy of white-grubs is known to occur in Mich- 
igan, Indiana, Wisconsin, Illinois, Iowa, Minnesota, South Dakota, and 
Washington. 
According to our observations the larva of P. vertebratus is the 
most beneficial of the asilids known to attack white-grubs. It is very 
common in certain parts of Wisconsin and Michigan where the common 
white-grub is a serious pest. The writer has several times seen the larva 
of this species attacking grubs in the field, most frequently in the sum- 
mer or early fall, when the grubs have become more or less inactive and 
have made cells preparatory to pupation.: It makes a small entrance- 
hole into the cell and through this attacks the grub, withdrawing if 
necessary to escape its mandibles. After it has weakened the grub, or 
if this is in the inactive prepupal or pupal stage, the predator may enter 
the cell and leisurely consume its host. In the summer and fall of 1914 
we found large numbers of the empty pupal exuviae of this fly pro- 
truding half their length or more from the ground in fields at Baraboo 
Fic. 20. Promachus vertebratus Say, 
larva attacking a white-grub. 
and Madison, Wis., and at Richland, Mich., where grubs had been de- 
structive in 1912 and the adult beetles of that brood had issued in the 
spring of 1914. 
The life cycle has not been completely worked out, but from the 
facts that we have kept larvae in confinement for two years and that’ 
larvae of one size and pupal exuviae are found common in the same 
locality only every three years, it is probable that the cycle is three years, 
as Dr. Felt has found to be the case with P. fitchi. The larva is pure 
creamy-white, smooth, cylindrical, and tapering at the extremities. It 
very closely resembles the larva of Erax, and is shown in Figure 20. In 
feeding, it punctures the host with its sharp mandibles and, inserting 
its head in the small opening, sucks the body fluids. This and the other 
Pe eS a 
