PSYCHE 
VOL. XXX. APRIL 1923 No. 2 
OBSERVATIONS ON THE FEEDING HABITS OF 
ROBBER FLIES. PART I. 
PROCTACANTHUS RUFUS WILL. AND P. BREVI- 
PENNIS WIED. 
By S. W. Bromley. 
Massachusetts Agricultural College, Amherst, Mass. 
One of the characteristic insects of the sandy plains along 
the Quinnipiac river in southern Connecticut during the hot 
sunny days of July is the large and handsomely-colored robber- 
fly, Proctacanthus rufus Will. Its rusty-orange abdomen and 
swift, undulating flight as it starts up in advance of the collector 
make it very conspicuous. The frequency with which one is 
seen bearing away some large insect that it has captured in- 
vites attention to what particular species are being taken. 
The flies are very active and hard to approach, taking 
wing at the slightest movement and flying long distances before a- 
gain alighting. In fact, the only times that they are at all easily 
captured is when they are encumbered with prey, and even then 
they are very wary and when disturbed carry such large prey as 
Polistes several rods before they again settle down. Because of 
these habits, it was very exasperating to stalk an individual 
over the hot sands only to have the specimen take flight just as 
the net was poised for the stroke. 
Of the prey taken, all were of the order Hymenoptera. I 
did not see them attack species of any other order, although it is 
probable that they would capture Hymenoptera-resembling 
Diptera if opportunity offered. No attention was paid by them 
to the Lepidoptera and Odonata that occasionally drifted over 
the sands. 
