G. C. Wheeler and J. Wheeler.
Veromessor lobognathus in North Dakota (Hymenoptera: Formicidae).
Psyche 63(4):140-145, 1956.

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VEROMESSOR LOBOGNATHUS IN NORTH DAKOTA
(HYMENOPTERA : FORM1,CIDAE)
BY GEORGE C. WHEELER AND JEANETTE WHEELER Department of Biology, University of North Dakota In our field studies on the ants of North Dakota we have been in the habit of identifying our collections of Pogo- nomyrmex by casual inspection with the unaided eye. This seemed adequate, since there is only one species of this genus in the state and since we knew of no other ant that could be confused with Pogonomyrmex. But after reading Gregg's interesting paper2 on Veromessor we hur- riedly re-examined our material under magnification. (See Fig. 1.).
Among a hundred nest-series of putative Pogo- nomyrmex occidentalis (Cresson) we discovered one of Veromessor lobognathus (Andrews) . This is only the sixth collection of this species, but it extends the range northward by 450 miles. Since almost nothing is known about its habits and ecology we hoped that our field notes would contribute something, but we found them disap- pointingly laconic: "Under flat rock 32 x 23 x 2" lying on north wall of east-west valley. ATYPICAL." The word "atypical" is significant for it shows that at the time we regarded the ant as P. occidentalis and a Pogonomyrmex nest under a rock was something we had never seen. Our error was not detected until the autumn or winter of 1955. Consequently we could not return to the site until the summer of 1956. By that time southwestern North Dakota had suffered a year of drouth and ants (except P. occi- dentalis)
were scarce and hard to find. We revisited the same hillside and literally "left no stone unturned"; in fact we turned them over twice- the second time after the late summer rains. But we found no trace of the This study was aided by a grant from the Louis W. and Maud Hill Foundation.
Gregg, R. E. 1955. The rediscovery of Veromessor lobognathus (Andrews) (Hymenoptera : Formicidae). Psyche 62 : 45-52.



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19561 Wheeler and Wheeler - Veromessor 141 coveted Veromessor. If moisture conditions improve, we plan to resume our search next summer.
Billings County, North Dakota. T. 140 N., R. 102 W., see. 1. On an ordinary map it can be located four miles north-northeast of Medora, in Roosevelt National Memorial Park (South Unit). The site is in the heart of the Little Missouri Badlands. June 12, 1954. Collected by G. C. and J. Wheeler, No. 556. Altitude approximately 2500 feet above sea level.
HABITAT
The nest was discovered in a tributary valley entering the valley of the Little Missouri River from the east. This tributary valley is short, narrow, steep-walled and about 200 feet deep at the mouth. At the bottom is a small intermittent stream with little or no flood plain. The soil is a sandy silty loam.
The south wall of the tributary valley is densely covered with a thicket of Rocky Mountain red cedar (Juniperus scopulorum Sarg.).
The thicket floor is covered with duff
and moss and is relatively humid.
In marked contrast, the nearby north wall-as the result of greater insolation - is treeless and sparsely beset with grass and low shrubs, such as sagebrush (Artemisia frigida Willd. and A. tridentata Nutt.), saltbushes (Atrip- lex spp.) and rabbitbrush (Chrysothamnus graveolens Nutt.). Yucca (Yucca glauca Nutt.) and prickly pear (Opuntia polycantha Haw.) are present but very scarce. The most abundant and conspicuous ant is the western harvester (Pogonomyrmex occidentalis) . Scorpions (Ve- jovis boreus Girard) are common under rocks. Our colony of Veromessor lobognathus was found under a rock halfway up the north wall. Its occurrence on a slope with southern exposure is significant in interpreting the distribution of this species, i.e., why a southwestern
species occurs so far to the north. "The Upper Austral Zone, the Upper Sonoran, or semiarid subdivision of which penetrates only into the warmest corners of the



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142 Psyche [December
State, is in no part sufficiently extensive to be marked by entirely characteristic mammals, birds, or plants. In its narrow strips along the Missouri Valley below Bismarck, down the Missouri and Yellowstone Valleys to Williston, along the Little Missouri Valley above the Killdeer Moun- tains, and on many dry, warm slopes between these Text figure 1. Thoracic profiles of (A) Pogonomyrmex nccidt~ntalis (Cresson) and (B) Verom,essor 1obRgnathu.s (Andrews), both x8.8. areas, it is strongly characterized. So near the edge of a zone, however, the slight inclination of a slope to the north reduces the heat receivedl from the sun's rays suf- ficiently to change the flora and fauna in part or wholly to that of the colder, higher zone, while a steep slope fac- ing the direct rays of the sun will attract many species of the warmer, lower zone above their normal limit^."^ THE LARVA
Genus VEROMESSOR Forel
Body curved ventrally, thorax only moderately stout. Body hairs sparse and short; of three types: (1) the shortest and most numerous, tip simple or bifid; (2) longer, Bailey, Vernon. 1926. A biological survey of North Dakota. US. Dept. Agric., Bureau of Biol Survey, North American Fauna, No. 49. p. 8.



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19561 Wheeler and Wheeler - Veromessor 143 with the tip bifid; (3) also longer, bifid, the branches short to long and recurved at the tip. Antennae minute. Head hairs moderately numerous, short, with the tip simple or bifid. Mandibles with the apex forming a long large round-pointed tooth which is curved medially; the two medial teeth prominent and round-pointed; a few spinules on the medial surface. Maxillae with the apex spinulose. Labium moderately spinulose. Dorsal portion of hypo- pharynx with sublongitudinal ridges ; ventral portion spinu- lose, the spinules minute and in numerous subtransverse rows.
Veromessor lobogmthus (Andrews)
(Text figure 2)
Body length (through spiracles) about 6.8 mm. Stout; diameter greatest at abdominal somite V, diminishing gradually to the anterior end and rapidly to the posterior end, which is broadly rounded. Whole body curved ven- trally. Anus ventral. Lateral longitudinal welts present. Leg, wing and gonopod vestiges present. Spiracles small ; the mesothoracic the largest. No spinules seen on the in- tegument. Body hairs sparse, short and uniformly dis- tributed. Of three types : (1) 0.036-0.094 mm long, with the tip simple or bifid, on every somite, the most abundant type; (2) 0.094-0.l156 mm long, with bifid tip, on the thorax and abdominal somites IX and X; (3) 0.078-0.156 mm long, bifid, with the branches short to long and re- curved at the tip, on the metathorax and abdominal somites I-IX. Cranium subrectangular in anterior view, with the occipital angles rounded, slightly broader than long. An- tennae minute, each with three sensilla, each of which bears a spinule. Head hairs moderately numerous, slightly curved ; short (0.036-0.086 mm long), with the tip simple or bifid. Labrum small, bilobed, breadth nearly twice the length; anterior surface of each lobe with 10 sensilla; ventral border with a few minute spinules; posterior surface spinulose, the spinules minute and in short arcuate rows, the rows transverse dorsally and longitudinal ven- trolaterally; posterior surface with two isolated sensilla



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144 Psyche
[December
and a cluster of three sensilla on each lobe. Mandibles rather small ; heavily sclerotized ; subtriangular in anterior view; the apex forming a long, rather large tooth which is curved medially; medial surface with two rather large round-pointed teeth on the distal half and a few ridges bearing spinules on the proximal half; anterior surface with a few longitudinal ridges. Maxillae with the apex spinulose, the spinules minute and in short arcuate rows; palp paxilliform with one lateral sensillum (bearing a spinule) and four apical (two small and bearing a spinule each and two larger and encapsulated) sensilla; galea digitiform, with two apical sensilla. Labium with the anterior surface spinulose, the spinules minute and ar- ranged in short transverse rows; palp a boss with five apical sensilla; an isolated sensillum between each palp Text figure 2. Larva of Veromessor Inbognathus (Andrews). A, head in anterior view, x47; B. left mandible in anterior view, xll7; C, larva in sidc view. xl4:
D and E, type 1 body hairs, x217: F. type 2 body 11;ur. x217; G find H, type 3 body hairs (with short branrhes) in side and ~~if:~ce view, x217; I and J. type 3 b>dy hairs (wit11 long brrn ,hw) in sirfru~ and side views. x217.



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19561 Wheeler and Wheeler - Veromessor 145 and the opening of the sericteries; the latter a short trans- verse slit in an anteroventral depression. Dorsal portion of the hypopharynx with sublongitudinal ridges, ventral portion spinulose, the spinules minute and in numerous subtransverse rows. (Material studied: six larvae from the nest cited above.)
Since this is our only representative of the genus we do not know whether it differs as much from its congeners as does its adult. It does, however, resemble the larva of the closely related genus Novomessor.




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