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PSYCHE

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S. M. Bromley.
Observations on the Feeding Habits of Robber Flies. Part I Proctacanthus rufus Will. and P. brevipennis Wied.
Psyche 30(2):41-45, 1923.

This article at Hindawi Publishing: https://doi.org/10.1155/1923/73859
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PSYCHE
VOL. XXX. APRIL 1923 No. 2
OBSERVATIONS ON THE FEEDING HABITS OF
ROBBER FLIES. PART I.
PROCTACANTHUS RUFUS WILL. AND P. BREVI-
P E W WIED.
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, Proetacanthus 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 takeflight 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.
Pu&e 30:41-46 (1923). hup Ytpsychu einclub orgtlWlO-IMLhtinl



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42 Psyche [~~ril
For aid in determining the species recorded, both from P. rufus and P. brevipennis, I wish especially to thank Dr. W. E. Britton of the Conn. Exp. Station who allowed me access to the Station collection, and to Dr. H. T. Fernald for the use of the Massachusetts Experiment Station collection. The insects taken from P. rufus are as follows: Sex of
Fly
Date
July 2, '22
It
July 8, '22
it
46'

it
44
ti
i 4
it
it

it
July 16, '22

ii
it
if
4 i
i i
44
i i
Locality
Hampden, Conn.

a
a
ti
it
it
a
a
44
tt
i t
it
Wallingfod, Conn.
it
44
44
it
it
it
a
it
Prey
Vespa vidua Sauss. (queen)
Pohstes variatus Cresson.
(worker)
A pis m,ellifera L. (worker)
Polistes pallipes LePel. (worker)
46 it,
Apis mellzfera L. (worker)
ii
it
it
44
it
ti
it
a
Pompiloides tropicus L. 9
A pis nzellifera L. (worker)
44
44
Polistes pallipes LePel. (worker)
Microbembex monodonta Say. Q
Tiphza inornuta Say. Q
I I
Elis interrupta Say. c?
A mblyteles rufiventris Brulle.
Hemi-hosonius SD? 9
Summarized Table of Prey
Hymenoptera.
14 A pis mellifera L. 1 Elis interrupts Say. 3 Polistes pallipes Le Pel. 1 Pompiloides tropicus L. 2 Tiphia inornata Say. 1 Hemipogonius sp? 1 Vespa vidua Sauss. 1 Microbembex monodonta Say. 1 Polistes variatus Cresson.
1 Amblyteles rufiventris Brull6.




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19231 Observations on the Feeding Habits of Robber Flies 43 From this may be seen that over 50% of the prey taken from the flies consisted of honey-bee workers. The explanation of the
presence of so many bees in such an uninviting environment as these sand areas is this: beyond the western edges of the fields where I made these observations were banks of sumac to and from which the bees were continually streaming, many taking their course over the sand plains not more than ten or fifteen feet from the ground. It was from these that the robber-flies took heavy toll. Where the flies were most abundant I oft,en saw one sweep upward and grasp a bee, only to fly so far with its prey as I approached that I was unable to locate it and obtain the record.
Several honey-bees that were taken from the flies were after- wards dissected and examined by Mr. R. E. Snodgrass of the Bureau of Entomology, with whom I was staying at the time, and myself. A specimen that the fly had dropped because it had consumed all parts possible was found to be nothing but an empty shell. Nearly all of the digestive, nervous, and mus- cular systems had been dissolved, probably by the introduction of an enzyme, and sucked out. The poison sac was intact, as was the tracheal system and all chitinized portions. A bit of the small intestine and unrecognizable pieces of other organs remained in the body cavity, but most of the internal struc- tures were gone. Examination of others in different stages of consumption showed the muscle tissue of the thorax reduced to a shredded mass and the muscles and brain in the head-capsule disintegrated. Whether or not this was accomplished by an enzyme secreted by the salivary glands, I do not know. Further work might determine this point.
An interesting point noted in watching the flies was the fact that although Psammocharids were the predominating and most conspicuous hymenopterous insects flying over the plains, the flies seemed to have trouble in capturing these. I watched them dart at these wasps on several occasions but the wasps eluded them by dropping to the ground and running through clumps of bunch-grass. They are occasionally captured, how- ever, and I was able to take the flies preying upon Psammo-



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44 Psyche [~~ril
charids in two instances, as shown by the list, but I never had the good fortune of seeing any in the act of capturing the wasps. Females of P. rufus were watched for oviposition habits. No attempts were seen to be made, but empty pupa cases were seen protruding from the sand. These, because of their size, were evidently of this species, indicating the underground life of the immature stages.
Recently, through the kindness of Mr. Nathan Banks, I was allowed to examine the collection at the M. C. 2. where two records of this species with prey were obtained. 9 P. rufus: prey, Polistes sp? Woods Hole, Mass., VII,19, 1893. A. P. Morse, Coll.
9 P. rufus: prey, Brew sp?$ West Springfield, Mass., VII, 26, 1915. H. E. Smith, Coll.
Proctacanthus rufus seems to be restricted to sandy areas such as those a,bove mentioned and I have never taken it in the fields and pastures frequented by P. philadelphicus except those in the immediate vicinity of the sand areas. That the insect is not more widely spread is a fortunate thing for bee-keepers. Another Asilid found in the same sandy areas as the above but less conspicuous and active is Proctacanthus brevipennis Wied.
This belongs to the same genus but is smaller and more of the color of the sand on which it alights. I found it to be far less abundant than its larger relative in the area studied. It will be seen from the list of prey that the type of insects captured by this species is quite different from that taken by by the last. Here half the species recorded were specimens of the beetle Anomala lucicola Fab. which is common on the sand fields and captured during flight, as is the case of all prey taken. The list of insects taken from P. brevipennis is as follows: s f 1 Date 1 Locality 1 Prey
1. Q
2. Q
3. 9
4 . Q
5. 9
6. c?
---
July 8, '22
Tuly 16,'22
::
Tulv 23.'22
Hampden, Conn.
6 i
Wallingford, Conn.
it
it
it
Anomala lucicola Fab.
64
Formica fusca var? 3'
Anomala lucicola Fab.
Zelus exsanguis Stal. Q
Sarcofihaga sp?




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19231 Observations on the Feeding Habits of Robber Flies. 45 Summarized Table of Prey.
Coleoptera Diptera
3 Anomala lucicola Fab. 1 Sarcophaga sp? Hymenoptera
Hemiptera
1 Formica fusca var? 1 Zelus exsanguis Stal. McAtee and Banks in their paper on the Asilidae of the District of Columbia (Proc. Ent. Soc. Washington, vol. 22. p. 26) record P. brevipennis as feeding upon Anomala sp. This fly evidently has a predilection for this genus of beetles. Most of the prey from both species were taken from fe- males, as one would naturally expect to be the case in preda- cious insects, for they are larger and more powerful than the males and require more stored-up energy for the discharge of of their sexual functions.




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46 Psyche [~~ril
NOTES ON THE DIPTEROUS FAMILY CYRT1D.E.
BY F. R. COLE.
Stanford University, California.
In 1919 the writer published a revision of the Cyrtidae of North America (Trans. American Ent. Soc., XLV, 1-79). There are some mistakes and omissions in this paper which should be corrected and some notes have accumulated on various species of the group.
Eulonchus marginatus 0. S.
There are two specimens of
this apparently rare species in the collection of the California Academy of Sciences, taken at Sobre Vista, Sonoma Co., Gal., May 8 (Kusche).
Ocncea helluo 0. S. A specimen taken at College Station, Texas, was sent to the writer by Mr. H. J. Reinhard. It is 12.5 mm. in length and answers the original description in most res- pects; it differs in that all the longitudinal veins reach the wing margin. In each wing there is an adventitous cross-vein in cell M-3, one in cell 1st R-5 in one wing and one in cell R-1 in both wings (see fig. 1).
Fig. 1.
Ocnaa helluo 0. S., wing.
Acrocera liturata Will. The writer has one specimen taken at Los Gatos, C,a,l., June 20, 1917. This is a female with very little black at the base of the scutellum. There is more yellow on
the abdomen than in the typical description. The species is evidently quite variable in coloration. Length 3 mm.



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