lnsectes Sociaux, Paris Masson, Paris, 1983 1983, Volume 30, n ~ 4, pp. 384-401 A BEHAVIORAL STUDY OF THE PRIMITIVE ANT NOTHONYR2~ECIA MACROPS CLARK B, HOLLDOBLER (1) and R.W. TAYLOR (2) (I) Department ol Organismic and Evolutionary Biology, MCZ Laboratories, Harvard University, Cambridge, Mass. 02138, U.S.A. (2) Division af Entomology, C.S.LR.O., Canberra City, ACT 2601, Australia. Re~u Ie 18 octobre 1982. Accept6 le 10 avril 1983. SUMMARY 1. Nothomyrmecia macrops workers forage individually; no recruitment communication or group retrieval of prey has been observed; prey items measure tess than 4 mm in length ; huntresses grasp live prey with the mandibles and forelegs and sting it to death. 2. Field and laboratory observations confirm that ~vorkers from neighboring nests can forage on a single tree 'without antagonism. Alien conspecifics might be attacked, however, if attempting to enter foreign nests. 3. Field and laboratory observations suggest that chemicaI trai!s do not play an impor- tant role:during homing by foragers, indeed they might not be produced. Mthough strictly nocturnal, Nothomyrmecia seems to navigate primarily by visual cues, possibly using the canopy silhouette overhead~ However, chemical markers might be important in localization and recognition of nest entrances. 4. No antagonistic behavior has been observed beZ'ween foragers from different colonies, yet in a laboratory test nestmates appear to shq',v a greater tendency to' cluster than non-nestmates. Wor&er interchange between neighboring laboratory nests ,was observed and experiments suggest that it is facilitated by loss of the queen in one colony. These results explain in part the findings of WAa~ and TAYLOR (1981) that Nothomyrmecia nestmates are not ~ways full sibs. 5. All records to date indicate that mature Nothomyrmecia colonies are monogynous, but can be founded by pleometrosis (TA~LOR, 1978). : In an experimentally assembled group oh I5 ~vor..kers ~vith 2 queens (neither of vghich was the mother of any of the worker~ i one queen exhibited dominance behavior to*,vards the other. The subordinate was finally expelled by the 'workers. 6, Nothomyrmecia employs chemical alarm communication when other ant species attempt to enter its nests. The mandibular gland secretion is an effective close-range alarm pheromone. Dufour's gland secretions also elicit attraction, but the ants react more slowly. Secretions from the pygidial gland appear to function as an atarm-repelle,at substance. BEHAVIOR OF THE PRIMITIVE ANT N. MACROPS 385 ZUSAMMENFASSUNG Fine verhaltensbiologische Untersuchun9 der primitiven Ameise Nothomyrmecia macrops Clark, 1. Nothomyrmecm macrops Arbeiterinnen furagieren einzeln ; Rekrutierungsvers~ndigung oder Eintragen yon Beute in Gruppen wurde nicht beobachtet. Die Beutestiicke sind gew.Shrdieh nicht Nnger als G.4 cm. Die Jggerinnen packen die lebenden Beuteinsekten rnit den Mandibeln und Vorderbeinen und jede Beute 'wird yon der Ameise gestochen. 2. Beobachtungen im Freiland und Laboratorium bestSitigen, dass Arbeiterinnen yon benachbarten Nestern am selben Baum Futter suchen kSnnen. Im Furagier-Areal ~urde kein antagonistiches Verhalten z"Mschen gleichartigen Fremden beobachtet. Gleichartige Arbeiterinnen k6•nen jedoch angegriffen werden, wenn sie in ein fremdes Nest eindringen. 3. Chemische Spuren spielen offensichtlich keine ~vesentliche Rotle bei der Heimfinde- Orientierung. Obgleich Nothomyrmecia bei Nacht furagiert, scheint sie sich haupts~ehlich visuell zu orientieren. Erste Versuehe deuten darauf hin, dass das "Baumdach-Muster" dabei eine ,wesentliche Rolle spielen kSnnte. Am Nesteingang 2<6nnten jedoch auch chemische MarJ~en entscheideade Erkennungs-und Orientierungshilfen darstellen. 4. Die Nesttreue von Furagier-Arneisen wird dutch die genaue Heimfinde-Orientierung und dutch eine Bevorzugung yon Nestgenossen gesichert. Arbeiterinnen vom selben Nest zeigen ira Versueh eine gr:Sssere Tendenz in dichten Gruppen zu sitzen als frerade Nothomyrmecia Arbeiterinnen. Dennoch haben wit ira Laboratorium Arbeiterinnen- Austausch zwischen Kolonien beobachtet. Die Ergebnisse mehrerer Versuche deuten darauf hin, dass der Verlust der K6nigin in einer Kolonie das Ab'wandern yon Arbeit- erinnen begfinstigt. Diese Ergebnisse erklfiren teiI'weise die genetischen Befunde yon WARY und TAYLOR (1981), wonach Nothomyrmecm Nestgenossen nicht iraraer voile Geschwister sind. 5. Alle bisherigen Ausgrabungen yon voli ent,wickelten Kolonien (10) deuten darauf hin, dass Nothomyrmecia in monogynen Kolonien lebt. Neue Kolonien :k6nnen jedoch pteometrotisch gegrfindet ~werden (TAYLOl~, t978). In einer experimentell zusarnmengesetzten Gruppe bestehend aus I5 Arbeiterinnen und zwei K/Sniginnen (keine davon ~war die Mutter der Arbeiterinnen), zeigte eine K,fnigin Dominanzverhalten gegenfiber der anderen. Die untergeordnete KSnigin wurde schliesslich yon den Arbeiterinnen ausgestossem 6. Nothomyrmecia setzt ein chemisches Alarm-Komraunfkationssystem ein, ~wenn Arneisen anderer Arten versuchen in ihr Nest einzudringen. Unsere Versuche zeigen, dass das Mandibeldrfisen-Sekret ein besonders effektives Alarrapherornon darstellt. Auch das Sekret dec Dufourschen Drfise 1,Sst Attraktion aus, jedoch ist die Reaktion tier Ameisen lang- saraer. Das Sekret der Pygidialdrfise scheint als A1arm.Repetlent-Substanz gegen andere Ameisenarten eingesetzt zu werden. INTRODUCTION The Australian ant Nothomyrmecia macrops (CLARK) is arguably the most primitive li~ng formicid, and therefore a species of special interest to systematic and beha~oral biologists (WILSON, 1971). Its original description was based upon two damaged worker specimens originating from southern Western Australia and coI!ected in the Summer of 1931-32 (CLARK, 1934). Despite much effort Nothomyrmecia was lost to prospective colIectors, and 386 B. HOLLDOBLER AND R.W. TAYLOR to science, for a further 46 years, until rediscovered by TAYLOR ill 1977. This resulted in the collection and study of captive colonies, initiating a major program of field and laboratory research conducted by TAYLOR and others. Some results of this ~r have been published (TAYLOR, 1978 ; H/fLLDOBLER and ENGEL, 1978 ; KUGLER, 1980 ; WARD and TAYLOR, 1981 ; WHEELER, WI~ELER and TAYLOR, 1980), and other studies are in progress in Australia, Europe and North America. We report here the results of further behavioral studies on communication and colony distinctiveness in Nothomyrmecia~ The single presently known population of N. macrops resides in Euca- lyptus oleosa-dominated mallee woodland near Poochera (32 ~ 43' S ; 134 ~ 50' E), southwest of Ceduna, South Australia, about 1 000 km east of the original collection site. It is more extensive than previously supposed but all its known loci lie veithin a 1 km radius. MATERIAL AND METHODS Our research ,was conducted during a brief field visit to the Poochera area in late September and early October 3980, supplemented by Tater experiments in Canberra, using three colonies excavated then (and designated A, B and C), along ~vith a number of captured foraging ~workers and three foraging queens. Each laboratory colony was housed in a stoppered test-tube nest (8 cm • O 2.5 era) fitted 'with a narro~v glass entry tube (O 0.6 era). The interior of each nest was kept moist *with ,water trapped at the bottom of the :tube by a Cotton-~r plug. Early observations showed that dim ambient light did not visibly disturb the ants, so the nests ~were kept uncovered. Each colony had access to a foraging arena, ~vhere small containers of honey~water ~vere provided, and insect prey ~vas available. This included several species of field-collected flies, and laboratory reared Drosophila adults. Other nestS, described belo-,v, 'were used for some experimental procedures. RESULTS Hunting behavior and homing We noted in the field several phenomena previously reported by TAYLOR (1978). Namely that Nothomyrmecia workers forage nocturnally on Euca- lyptus oteosa trees, leaving the nests only after dusk and returning by d~wn, with all above-ground activity ceasing by approximately 30 minutes after sunrise; that the ants forage individually, with no evidence of recruitment or group retrieval of prey ; that prey objects included various small insects, generally less than 4 mm long; that foragers observed on tree treks late at night did not return positively in a manner allcrvcing them to be easily tracked, even when carrying prey or fed to satiation with honey (*) and that (*) We observed three workers carrying insect prey down a tree trunk (~ig. 2) at 22:30; 23:05;23:30 hours. These ~vere lost in the leaf litter at the base of the tree; so it is not ~mcmm if they returned directly to their nest. BEHAVIOR OF THE PRIMITIVE ANT N. MACKOPS 387 nests could be most easily located at first light, when the last returning foragers move very positively down the tree trunks and are readily tracked from there across the ground to their nest entrances. We also confirmed by direct observation the findings of WARD and TAYLOR (1981), that workers from neighboring nests can forage on the same tree (fig, 1). .,o NesfE ; !m / Fig. 1. -- Map of ~wo neighboring nests of N. macrops. Foragers:from both nests had simultaneously visited the 11 Workers same tree, as indicated by their homing routes to the nests at da~n ; 17 ~vorkers ~vere counted returning to nest I and tl workers to nest II. Abb. 1, -- Lage zweier N. macrops Nester. Arbeiter yon beiden Neste~ fura- Ne't ~~sTree gierten am selben Baum. 17 Arbeiter kehrten zu Nest I zurfick und 11 Arbeiter