Great Basin Naturalist
Volume 56 Number 4 Article 6
11-21-1996
A field study of the nesting ecology of the thatching ant, Formica obscuripes Forel, at high altitude in Colorado
John R. Conway University of Scranton, Scranton, Pennsylvania
Follow this and additional works at: https://scholarsarchive.byu.edu/gbn
Recommended Citation Conway, John R. (1996) "A field study of the nesting ecology of the thatching ant, Formica obscuripes Forel, at high altitude in Colorado," Great Basin Naturalist: Vol. 56 : No. 4 , Article 6. Available at: https://scholarsarchive.byu.edu/gbn/vol56/iss4/6
This Article is brought to you for free and open access by the Western North American Naturalist Publications at BYU ScholarsArchive. It has been accepted for inclusion in Great Basin Naturalist by an authorized editor of BYU ScholarsArchive. For more information, please contact [email protected], [email protected]. Great Basin Naturalist 56(4), © 1996, pp. 326-332
A FIELD STUDY OF THE NESTING ECOLOGY OF THE THATCHING ANT, FORMICA OBSCURIPES FOREL, AT HIGH ALTITUDE IN COLORADO
John R. Conwayl
AB~TRAGe-A field study of the thatching ant, Formica ohscuripes Forel, at 2560 m elevation in Colorado provided information on mound density, composition, dimensions, and temperatures; worker longevity; and mite parasitization. Density was 115 moundsftla. Mounds had 1-52 entrances and PeromysCU8 fecal pellets in the thatch. Mounds conserved heat and exhibited thermal stratification. Excavations of 4 nests revealed depths of 0.3 m to almost 1 m, novel myrme cophiles, and 0-198 wingless queens per nest. Marking experiments demonstrated that some workers overwinter and live more than a yea!:
Key words: Formica obscuripes, thatching ant, Colorado, ant mouruls, myrmecophiles.
Formica obscuripes Fore! is in the Formica MATERIALS AND METHODS mfa-group (Weber 1935) and rauges from Indi ana aud Michigan westward across the United The study site is in Gunnison County north States and southern Canada. It is one of the of Blue Mesa Reservoir aud west of Soap most abundant ants in western North America, Creek Co. Rd. in western Colorado at au alti especially in semiarid sagebrush areas (Gregg tude of 2560 m. Field observations were con 1963), and has heen found at altitudes up to ducted 5-6 August 1990, 20 June -11 October 3194 m (Wheeler and Wheeler 1986). 1992, 28 June-16 August 1993, 29 June-31 11,e objective ofthis field study was to com July and 14-16 August 1994, aud 3, 29-31 July pare mound density, formation, composition, and 15-16 Augnst 1995. The area, dominated dimensions, aud temperatures, worker longevity by big sagebrush (Artemesw tridentata Nuttall) and parasitization, nest depths, myrmecophiles, and to a lesser extent by rubber rabbitbrush aud the number ofwingless queens per colony (Chrysotlwmnus nauseosus [Pallas] Britton), is ofthis species at high altitude in Colorado with adjacent to a grove of quaking aspens (Populus findings from lower altitude studies in Colo tremuloides Michaux). rado (Jones 1929, Gregg 1963, Windsor 1964), The locations of 85 mounds were mapped Idaho (Cole 1932), Iowa (King aud Sallee 1953, in a study area (64.6 m X 114 m) using a sur 1956), Michigan (Talbot 1972), Nevada (Clark veyor's trausect and compass in July 1993 to and Comanor 1972, Wheeler and Wheeler determine density. 1986), North Dakota (McCook 1884, Weber The diameters aud heights of 97 mounds in 1935), Oregon (McIver aud Loomis 1993, the study area and surrounding area were mea McIver aud Steen 1994), Washington (Hender sured. The number of entrances per mound son aud Akre 1986), aud Cauada (Bradley 1972, was determined by inserting sprinkler flags 1973a, 1973b). Although this species seems to into the active openings on each mound. be most common at altitudes of 1524-2743 m Mound temperatures were measured with a in the mountainous states (Gregg 1963, Wheeler Model 100-A VWR digital thermometer probe. and Wheeler 1986), the highest previous study Sixty-seven temperature measurements were site was at au elevation of 1550 m (Clark aud made on 34 mounds in the evenings (1915-2045 Comanor 1972). It is hypothesized that cli h) 2-14 July 1993 by inserting the probe matic and vegetational changes associated with approximately 15 em into the top ofeach mound. higher altitude may alter the nest ecology of The temperatures of 4 of these mounds were this species. also recorded in the afternoon (1538-1600 h)
IDepartment of Biology. Univcn'ity ofScranloll, ScnmtOIl, PA 18510.
326 1996] NESTING ECOLOGY OF THATCHING ANT 327 on 2 July 1993. In addition, hourly tempera deer mouse (PeromysclIs tn1111icul. MOUND #3 JULY 16-18,1994 MOUND #14 JULY 18,1994 35.0 35.0 30.0 30.0 C fT'"" / / f'..... C e 25.0 l I e 25.0 n , / n t / I ...... "...... I ; .II" t i ..... 20.0 I 20.0 9 ,';... ,1/" r Ii _ .., 9 .'.... r a 15.0 , ..R a 15.0 d d e 10.0 e 10.0 5.0 5.0 0.0 l-+--<...... -....-....-...... 0.0 :1:--0--0-..,....,....,....,..-..,..,.....,.....,.....,...... 7 8 9 10 11 12 13 14 15 16 17 18 19 20 7 8 9 10 11 12 13 14 15 16 17 18 19 20 Time of Day Time of Day -e- Mound Top -.... Mound Base --- Mound Top -.-. Mound Base -0- Air N'" Ground _..... Ground -0- Air Fig.!. Average mound-top, mound-base, ground, and Fig. 2. Mound-top, mound-base, ground, and air tem air temperatures around a mid-sized Formka obscuripes peratures around a large Formica obscuripes mound from mound from 0700 to 2000 h on 16-18 July 1994 at 2560 m 0800 to 2000 h on 18 July 1994 at 2560 m in Colorado. in Colorado, Hourly top and base temperatures showed d). However, 2 workers marked on a mound thermal stratification. Average top temperatures between 7-9 July and 15-27 July 1994, respec were 3.2°C and 4.1°C higher than average tively, were observed on 30 July 1995 on base temperatures for the large and mid-sized another mound and on the original mound. mounds, respectively. However, for the small Thus, some workers overwinter and live more mound the stratification was reversed: average than 1 yr. top temperature was 3.5°C lower than the Mites average base temperature. The poor thermal regulation of smaller Mite infestation was not common. Orange, mounds was also reflected by a greater fluctua spherical mites were noted on only 1 worker at tion of hourly top and base temperatures. Daily 3 of the many mounds observed. The largest ranges oftoplhase temperatures were 7.6/8.7°C, number of mites observed was 4-5 on the tho 13.3/15.9°C, and 13.8/26.3°C for the large, mid rax and gaster of 1 worker. sized, and small nests, respectively. Thus, larger Excavated Nests mounds exhibited less daily temperature fluc tuation than smaller mounds. Each of the 4 nests excavated contained numerous workers, larvae, and pupae, but the Worker Longevity number of wingless queens per nest varied Most marking experiments (n = 14) indicated greatly: 0, 1, 32, and 198. No winged reproduc that some workers live 19 to 44 d (mean = 31.6 tives were found except a male in 1 nest. The 1996] NESTING ECOLOGY OF THATCHING ANT 329 MOUND #98 JULY 17, 1994 ers); and Lepidoptera (F Noetuidae-larvae; Table 1). 45.0 DJSCUSSION A:.'JD CONCLUSIONS 40.0 The extrapolated density of 115 mounds/ha is about 1.8 times greater tI,an the highest den C 35.0 sity reported: 64jha of Jack pine in Manitoba e (Bradley 1973a). n 30.0 Colonies are known to be polydomous and t to reproduce by budding (Herbers 1979). Some i 25.0 primary mounds and small secondary mound 9 lets along trails appeared and disappeared in r 20.0 our study area over the years as previously a reported, and some may have moved. For ex d 15.0 ample, a primary mound that was active in e 1990 was largely deserted by 1994 and mm 10.0 pletely abandoned io 1995. Colonies have been reporttxJ to move at lea:-;t 3 times during their We and to move 18 m from their original 5.0 location, or 1.:h33 m after transplantation (Brad ley 1972, 1973a). King and Sallee (1953, 1956) 0.0 7 8 9 10 11 12 13 14 15 16 17 18 19 20 noted desertions of many old ncsts and the establishment of1 or more new oncs from each Time of Day ofthem. -e- Mound Top ~.... Mound Base All our mounds were in open sagebrush ex cept for 2 built around aspens at the forest edge...... Ground -0- Air Weher (1935) also noted that most mounds are in the open, but did Hnd some mounds par Fig. 3. Yluund-top, mound-base, ground, and air tem tially shaded and 1 enormous mound almost peratures aruund a small FonJ1ica obscuripes mound from completely shaded in an aspen grove. 0800 to 2000 h on 17 July 1994 at 2560 Tn in Colorado. In our study, 63 of98 mounds (64%) showed evidence of being built around sagebrush as depths of the nests were 0.3 m (estimated), 0.3 reported hy Weber (1935), but a few were huilt m, 0.64 m, and 0.97 m. around other structures such as trees and a The uest excavated in 1993 mntained the fencepost. Weber noted that workers kill sage following arthropods: psendoscorpioD5, collem bnlsh by chewing bark at the buse and spraying bolans, beetles and beetle larvae (I Ctenicem formic acid on the cambium. After 3 months, sp. [E Elateridae] and 4 EZeodes sp. [E Tene the stem is removed to form a longitudinal pas brionidae]; Table 1). sage in tI,e center of the mound leading to the The following insects were identified in the main entrance. 1994 nest Collembola (F Entomobryidae); Hom Weber (1935) reported that mounds are opteru (F: CicadelJidae-1 immature, F Aphid composed of slightly longer twigs (1-12 em) ida~2 immatures); Hemiptera (F Anthomri than the ones we measured (0.4--8.9 em), but dae-1 specimen); Coleoptera (F Cureulion these slight differences may simply reflect the idae-5 adults, F Scarabaeidae-1 adult and availabUity ofmaterials. CremastocheiZtlS pupa and larval skio, probable A new discovery was the presence of fecal F Crn"bidae-1 adult, probable F Anthri pellet.s of P. maniculatus or MicrottlS (Clark bidae-2 larvae, E Tenebrionidae-unidenti personal communication) on the surface and in fied larvae, probable Eleodes sp. larvae, and the thatch of Colorado mounds. Since workers Eleodes sp. pupae, F Cerambyeidae-Lcpturi were never observed canying pellets to mounds, nae, probable [",ptum sp. larva); Diptera their onwn is unclear. (probable E Asilidae-pupa); Hymenoptera (F Although Clark and Comanor (1972), Talbot Formicidae-fcw TapiMma sessile [SayI work- (1972), and Wheeler and Wheeler (1986) 330 GREAT BASIN NATURAUST [Volume 56 TAtfLI::: L Arthropods in Formica OOSCU1lpes Forel nests Coleoptera (continued) reported in the liter reported mound diameters within the range The number, size, position, and activity of we observed (9--142 em), Weber (1935) noted a mound entrances changed over time as re much greater range (13-335 em), but a smaller ported by Weber (1935). The number of en mean diameter (43 em) than we found (65 em). trances per mound in our study, 1-52, is close Talhot (1972), Clark and Comanor (1972), to tbe range of3-50 per mound reported (Cole and Wheeler and Wheeler (1986) noted 1932, Wheeler and Wheeler 1986). In the early mound heighls in the range we measured morning ants use openings in the sunlight; Jatel' (6-58 em), hut Weber (1935) reported lower as the temperature rises they use only shaded heights (2.5--46 em) and Henderson and Akre entrances as reported hy Weber (1935). Ilen (1986) reported mounds up to 1.22 m high. derson and Akre (1986) speculate entrances are Somewhat lower (20 em) and higher (30 em) opened during the day and closed with thatch mean heights were recorded by Weber (1935) at night to help control nest temperatures. and Wheeler and Wheeler (1986), respectively, Our mounds, especially mid-sized and large than we found (26 em). ones. were generally warmer than ground and 1996] NESllNG EcoLOGY OF THATCHING ANT 331 air temperatures and exhibited thermal stratifi TenebIionidae--EleoMs sp., and F. Ceramby cation Ii'om top to base. Weber (1935) and cidae--probahle Leptura sp.; Table 1). Andrews (1927) also noted that mounds are On the other hand, Windsor (1964) and warmer than the ground, and Andrews reported Henderson and Akre (1986) reported 3 major that the upper parts are warmer than the lower groups not fonnd in our limited sampling: parts of mounds. The differential between our Arachnida (small spiders), Thysaoura (silverfish), mound-top and air temperatures was greater in and Orthoptera (F Gryllidae). In addition, the evening than in the ahemoon. Small mounds Weber (1935), Windsor (1964), and MacKay sbowed a reversal of thelmal stratillc-ation and and MacKay (1984) noted many dipteran and greater hourly fluctuation of top and base tem coleopter:m families not in our nests and new peratures, which is indicative of poorer ther genera and species in a few of the same fami mal regulation. lies found in our nests (Table 1). Marking expedments suggest that worker The relationship of these myrmecophiles longevity is olien sbort but that some workers with the host colony is unclear. Larval and overwinter and live more than a year, Little adult coleopterans and noctuid lmvao may use information is available on the longevity of the chambers for hibernation or development worker ants and none was found for this species. (Weber 1935). Staphylinid beetles may prey Although maximum longevity is known to be 3 upon brood or workers. Jones (1929) suggested yr for workers of some species, such as Aphae that lepidopterau, coleopteran, and dipteran nogaster mdis (Emery), for others, such as larvae are tolerated becanse they feed on Solenopsis inDicta Buren, it is only 10-70 wk decaying vegetable matter in tl,e nest. Cmmas (Holldobler and Wilson 1990). tocheilus is a well-known symbiont in the nests Mites were found 00 only 3 workers in our of a number of ant species (HoUdobler and stndy area. Weber (1935), on the other hand, Wilson 1990). The scarab genus Euphoria may noted that mites (Parasitidae, Tyroglyphidae, be a symbiont treated with indillerence by the Uropoda sp.) were common on workers and host colony (Wheeler 1910). On the other hand, sexuals, especially on the tibia-tarsal joint, and ants are aggressive to other guests, such as the estimated over 200 on 1 queen. myrmecophilous cricket (Mynnecophila rnanni Schimmel"; Henderson and Akre 1986). Excavated nests varied in depth from 0.3 to Weber (1935) reported 3 ant species in nests 0.97 m, or less than the maximum depth of (Table 1) and noted that Leptothorm: hirticomis 1.37 m noted by McCook (1884) and 1.58 m Emery may prey upon brood or isolated work reported by Weber (1935). Weber specnlated ers. Tal1itwma sessile, one of the species in our that the water table (below 1.52 m) limits nest nests, often steals honeydew from thatching depth. ants throughout its territory, but seems to elicit Nests excavated from 27 Jnne to 6 August little defensive response (Mclver and Loomis did not contain winged reproductives except a 1993) male in 1 nest. This finding dillers from Cole's The high altitude of our stndy site did not (1932) observations oflarge numbers ofwinged seem to significantly alter nest dimensions and reproductives through June and July. ecology, but the work did provide new Hndings Many species of Fonnica are polygynous on this species, such as the greatest mound (Kannowski 1963). The number of Wingless density per hectare, Hrst report of probable P. qneens pcr Colorado nest varied from 0 to 198 maniculatus fecal pellets associated with mound (Conway 1996). The latter number lar exceeds thatch, new information on tlle thennal prop the 2 or more queens per colony reported by erties of mounds, new information on worker Cole (1932). longevity, greatest number of wingless queens The following arthropod groups found in reported in a nest, and possible new myrme our excavated nests had not been reporled cophiles. associated with this species: pseudoscorpions, collembolans (F Entomobryidae), homopterans ACKNOWLEDGMENTS (F Aphididae, F Cicadellidae), hemipterans (F Anth(x.'oridae), dipterans (F Asilidae), and cole Support for this research was provided by opterans (F Carabidae, F Anthribidae, E Cur grants fwm the Howard Hughes Medicallnsti cnlionidae, F. Elateridae-Ctenicera sp., F. tnte through the Undergraduate Biological 332 GHEAT BASIN NATURALIST [Volume 56 Sciences Education Program in 1993-94 to the Ht"lUJJOUl,ER, B., AND E. O. WII...WN. 1990. The ants. Bel following University of Scranton students: John l.:nap Press of lIarvard Ulliversity Press, Cambridge, MA. 732 pp. Bridge, Tom Sahalaske, Anthony Musingo, and JUNES, C. H. 1929. Ants and their relation to aphids. Bul •leanne Rohan. 1 would also like to thank the letin ofthe l..olorado Agricultural Experimcnt Station Systematic Enlnmology Laboratory in Beltsville, 341, 1-96. Maryland, for identification of myrmeeophiles; KING, R. L., AND R. M. SALLEF.. 1953. On the duration of William Clark at the Orma Smith Museum of ncsts of Fonnica obscuripe8 Forel. Proceedings ofthe J. Iowa Academy of Science 60: 656-659. Natural History, Albertson College of Idaho, in . 1956. On the half-life of n~ts of I-oonica ohscur Caldwell, Idaho, for identification of mam ---cipe:-':s Fore!' ProceediDJ.t.~ of lhe Iowa Academy of Sci malian fecal pellets; and the Forest Service in ence f13: 721-123. Gunnison, Colorado, for identification ofplants. KANNOWSKI. P. J. 1963. The flight activities of fonnicine ants. Sympos.ia Ccnctica e1 Biologica rtalia 12: 74-102. MAcKAY. E. E., AND W. P. MAcKAv. 1984. Biology of tlle LITERATURE CITED tha(cbi.n~ant liOnnica 1wemcrrl1Oidoli'J Emery (Hyme noptcra: Formicidae). Pan-Paci.fic Entomolo~ist 60: ANIJI\EWS, E. A. 1927. Ant-mounds (IS lo tempemture nnd 79-87. sunshine. Journal of Morpho]o!-!:y and Physiology 44: MANN, W. M. 1911. On some north western ants and their 1-20. guests. Psyche 18: 102-109. DHAIJU,y, G. A. 1972. 'lransplantin.g Formica ohscurlpes McCOOK, H. C.1884. The rufous or thatching ant of Dakota and Dolidtoderus tascherWergt (Hymenoptera: f