In the Ant Tetramorium Caespitum Mayr. I

ACTA NEUROBIOL. EXP. 1975, 35: 29!3-309

ETHOLOGICAL STUDIES IN THE ANT TETRAMORIUM CAESPITUM MAYR. I. FORAGING AND BUILDING BEHAVIOR

Jan DOBRZANSKI and Janina DOBRZaSKA

Department of Neurophysiology, Nencki Institute of Experimental Biology Warsaw, Poland

Abstract. Carrying heavy objects is a common element in the foraging and building behavior of ants. The initial stages of this behavior, i.e., lifting and moving in T. cnespitum displayed as stereotyped patterns of movement. These patterns do not improve as the ants become older and more experienced, which suggest their congenital nature. Growing experience of ants is manifested in the later stages of the transportation of heavy objects, and especially in entering the correct opening of the cest with the carried prey. When a foraging ant leaves its nest to return to the prey it initially moves in the general direction of its objec- tive. It is not until a certain distance from the nest is reached, that the ant is able to use olfactory stimuli to locate and follow its previous path. These observations indicate that the representatives of this species do not learn an exact way to and from the nest but instead have a memory for direction. The congenital character of these basic elements of foraging and building behavior allows the existence of a social organization without a division of work and foraging areas.

INTRODUCTION

One of the authors had suggested a few years ago (4) that T. caespi- turn has no division of grounds between the foragers, so characteristic phenomenon in Formica species. In the course of our many years lasting studies in T. caespitunz (T. c.), further differences in social organization when compared with Formica species became noticeable. 300 J. DOBRZANSKI and J. DOBRZANSKA

The object of present investigations is to permit an analysis of the specificity of foraging ancl building behavior in an effort to differentiate its inborn and acquired elements.

METHODS OF MARKING

Ants were marked using wire rings (6). In Formica species the ring could only be placed between petiole and abdomen. In Myrmicinae species it was possible to place rings in two or three constrictions along their complex petiole. By the use of double-or triple-colored wires it was possible easily to identify individual ants. However, because of the minute weight of Tetramorium ants it is not good to use more than one wire ring on their petiole. Therefore the possibilities to discriminate one mark from the other are limited in Tetramorium and identification of indvidual representatives of the species could only be done by placing a single colored rings around one of three different parts of the petiole, T. c. workers may reach a length of 2.3 to 3.5 mm, i.e., in many cases they may seem to be of L. brunneus' size. But contrary to the latter and even the thin Myrmica ants, Tetramorium are much slimmer, which accounts for the need of using very small rings. Builder ants working in defined areas are relatively easy to observe. Ants, especially the tiny Tetramorium, are not easily distinguishable outside of their nests. Still less observable are the ring-marked individuals. The use of a magnify- ing glass is necessary to learn if and with what color a given ant has been marked. When analysing the data one has to realize that the marked individuals found outside the nest may, contrary to the builder ants, represent only a fraction of the actual number of the individuals. For single observatjons individual ants can additionally be marked by painting their abdomens. However in the case of T. c. the paint does not remain on the animal for longer than 2-3 hr. Therefore this method can only be used in short experiments, e.g., on information about the capture of prey.

FORAGING BEHAVIOR

Tetramorium caespituin are omnivorous (1). They bring grass seeds of many kinds to their nest (9, 16, 22, 25, 28). According to Arnoldi (1) these ants lead a predatory life and hunt on a large scale. Leftovers from larger species of ants are also used as food. Moreover T. caespitum, similar to M. scabrinodis, forage on the victims of fights between other species of ants, carrying wounded and dead ants from the battle- fields (10). For this reason Lubbock called them "hyena-ants" (18). ETHOLOGICAL STUDIES IN ANTS (I) 301

Because of this way of life these ants do not have a protected foraging territory: they forage mainly on the foraging areas of other species of ants. With this way of living, extremely important is the ability to carry the trophy to the home-nest quickly and skillfully. A single ant readily seizes and carries home small pieces of food. Social mechanisms of foraging are revealed most emphatically when a piece of food is found that is too large for a single ant to carry. In order to stimulate this condition in our experiments, flies were pinned to the ground with pine needles (to simulate their great weight). Dur- ing unsuccessful attempts to lift the flies, lasting 5-6 min, we marked a primary forager (PF) by painting. -4s soon as the forager realized that moving of the trophy was beyond its physical capabilities, it rushed directly to the nest, entered it and almost immediately re-emerged, followed by a few, sometimes more, nestmates. They would move in single file to the pinned fly, and altogether pull it from the needle and carry the trophy to the nest. Alternatively, they would break the flies' bodies into pieces and individually carry the pieces. This process required many return journeys. This description is a general outline of the recruitment behavior of T. c. However, from more detailed observations it is clear that those "expeditions" not always proceeded so smoothly. Very often the PFs go astray on the return journey from the nest to the captured object and cannot find it again. To explain this we traced the path from the capturd ed object to the nest with pine needles and observed that the PFs (lead- ing some nestmates) rarely looked for their own trace when re-leaving the nest. Most often we watched that the PFs moved initially in the ap- proximate direction of the prey and it was not until 5-10 cm from the home-nest, that the ants began to zigzag until they located their own path which they quickly followed to the prey. Sometimes, however, the PFs were for a long time looking for their trails and it even happened that they could not find them and the prey was finally lost. We once observed a PF for 15 min while it tried to find its prey which was 5 cm from the nest. By the time it found the prey, the PFs' helpers were last and it had to return to the nest for more help. The PFs sometimes located their prey without troubles but lost their helpers. After two or three journeys back and forth from a captured object to the nest, the ants were able to make those journeys without hesita- tion. Similar phenomena were observed with foraging ants returning to their nests. A forager alone or with its burden has often, already near to its nest, difficulty in finding the proper entrance opening. It was possible to observe cases of individual adjustments to this situation. An 302 J. DOBRZAIQSKI and J. DOBRZANSKA

ant returning home used to leave its burden in the vicinity of the nest while it found and touched the proper entrance opening, whereupon it would return to the load and carry it home following the corrected route. In another situation when the trophy was heavy and carried by several ants, one of them left the trophy a feu. centimetres away from a group cf six entrance openings, found the proper entrance of the nest, touched it and returned to the trophy to correct the direction of movement which nad been assu.med by the helpers. Since a number or helpers tool< part jn the action, the capture very soon went out of the correct way. After the second repetition of t'ne leader's maneuver the prey finally reached the entrance of the nest. We repeat that examples of the behavior described above are not typical and were acquired as individual adjustments. Most frequenly we observed a single ant with a burden, wandering around for a long time before reaching the correct entrance to the nest. The great majority of lost paths occurred in the immediate vicinity of the nest; this suggests a lack of individual marking of olfactory trails (2) which made it im- possible for an ant to identify its own path amongst the large number of its nestmates' trails. The foraging area can extend to more than 60 m2 (3, 27), and the search for lost trails over such an area could only suc- ceed if the general direction of the search was known. The bel~aviorof forager ants indicates that they probably can recognize direction. The mechanism of this recognition is most likely baszd on the analysis of polarised light (28).

BUILDING BEHAVIOR Ethological studies in E'or?qica species by one of the authors (7) have indicated that only certain elements of its building behavior are inborn. These are a tendency for seizing the building material, lifting it onto an anthill and placing it parallelly to the surface. Manipulatory capacities such as: selecting of proper building material, the ability to effectively seize and carry it past obstacles and mounting the material into the nest construction are individually acquired by trial and error. Such investigations in Tc encounter the complementary methodical difficulties. This species builds hcterogcnous nests (18, 22, 24), but the basic building material is sand. In the woods with poor undergrowth nests are build straight in the ground; they usually lack anthills such as can be seen in the grass (21). Tho entrances and exits are holes in the surface of the ground. Large complexes of holes, when spread over a surface area of up to 1 m2, are hard to identify as a single nest, a colony of nests or even as a complex of different socjetes. We have based our analysis on the very ETHOLOGICAL STUDIES IN ANTS (I) 303

suggestive assumption of Wasmann and Brun - cited by Escherich (9) - that only polygynical species create polykalical colonies by splitting. However, Torossian (26) stated that the monogynical species Dolichode- rus quadripunctatus can create polykalical colonies, yet it is clear from his paper that splitting were only daughter-nest without females or offspring. Thus, this example does not contradict the assumption of Was- lnann and Brun; accordingly, we considered monogynical T. c. (19) as a non-colonial species. Consequently, when we observed ants communi- cating between holes, we concluded that these holes belonged to one large nest. Taking up observations on one of the entrance openings we used to mark the workers at their building activities. The marked individuals were very soon noted to carry out the same functions. After a consider- able number of ants had been marked, it appeared that the same individuals were seen building at different holes at times up to 75 cm apart. The only visible building activity in the nests of T. c. is the carrying of particles of sand out of the nest and placing them near the entrance opening. This function is too simple to allow large behavioral differences io be noticed in the builders. A.t most, only small differences (caused by variability of individuals) such as an individual's speed, perseverance and degree of timidity were observed. This accounts for the difficulties in investigations of the hereditary and acquired building behavior of ants living exclusively in ground nests. Therefore, detailed observations were obtained using complexes of entrance openings located in the abandoned nests of F. pratensis. Formica species build their hills using needles and sticks, often carrying them over a large distance. When Fornzica ants abandon their nests most large pieces of building material are often taken along as they move to a new nest. Small pieces of building material are left in the abandoned nest. The unconserved internal corridors col- lapse when the hill settles under atmosphere conditions and the area be- comes hollow and contains a mixture of grass and sand. Tetramorium caespitum ants choosing such an area for their own new nest have to deal with atypical building materials, which are still very large in relation to their small size. Instead of using soil and sand these ants use small sticks and pieces of pine needles etc., which are normally not deep- ly buried. Necessary also were the comparative studies of the building behavior of the ants which had not experience with this kind of building rnaterial. To this end we selected n~stslocated on meadows or paths, where there was no wood-bedding but instead only soil and sand. We covered entrance openings with pieces of pine needles, thorns and sticks, thereby forcing the workers to use building materials previously encountered only sporadically at most. 30-1. J. DOBRZANSKI and J. DOBRZANSKA

We should point out that the anatomy of ants puts them in a very difficult position from the point of view of seizing and carrying elongate objects. The jaws are oriented such that the ant must hold the piece parallel to its body axis; to do this the ant must, as a matter of fact, stand upon the very piece that is to be carried. Studies on Formica species have shown that new worker learn to deal with building materials by trial and error (7). The first movements of T. c. workers resembled the behavior of beginning Formica workers; with all legs on the object, the animal tried to lift it with its jaws. Yet we never observed in T. c. the stage of a chaotic struggle or shifting positions in relation to the object, which are so typical for beginning Formica ants. T. c, workers did not show any clumsinness toward the building material. Standing on a stick they would raise all four hind legs into the air and grasp the stick with their large jaws while standing on the object with front legs. Bending their front legs, the ants made several side movements with their bodies simultaneously trying to grip the ground with hind legs. Each time their hind legs found a support, the ant tried then to raise their whole bodies together with the stick held firmly in the jaws. If this attempt to lift the body failed. because of insufficient support, the same maneuver was repeated until the piece had been satisfactorily moved. These actions all took place quickly and in a stereotyped manner. The movements were effective and decisive. The finding of support and moving of an object was usually completed within 5 to 15 sec. Differ- ences in the behavior of individual ants seemed to depend exclusively on the presence or absence of a good grip for the hind legs. If the ground around the stick was soft (e.g., small needles) and the grip poor, lifting was not possible and the process of carrying the stick became prolonged. Therefore, when the ?'c workers are performing the first stage of manipulating of building material (i.e., picking up the object, lifting it and moving from its original place), they use stereotypical patterns of movements. If the motor reactions were acquired in the process of a very rapid or early learning, then motor proficiency would in very young individuals be under-developed. As a consequence of improvement of more experienced workers, individual differences would also result. We did not observe these symptoms. On the other hand we should not ex- clude completely the existence of such improvements, so subtle that we might be unable to observe them. However, on the basis of these observations, concluded several hundred times, as well as our experience when studying Formica species, we consider it rather unlikely that we have overlooked any significant differences in motor behavior. And so we con- clude that these patterns of movements have an inborn character. ETHOLOGICAL STUDIES IN ANTS (I) 30.5

THE PROBLEM OF DIVISION OF LABOR

The existence of stereotyped patterns of movements points to great frequency and biological importance of the performed motor action. Meanwhile the patterns described above have dealt with building materials seldom encountered by this species of ants. It was, therefore, necessary to investigate another, natural form of activity always requiring similar skills such as carrying food to the nest. Detailed observations have shown that the ants when carrying heavy or struggling prey performed movements of the pattern identical to the above described. It was characteristic that the ants performed the same maneuvers to find support for their hind legs and lift the prey together with the whole body. A similar set of movements was observed in young ants provoked (by destroying a part of the nest) to leave their nest for the first time. In the following examples we wish to emphasize the grasping power of ant's legs and jaws. A big blowfly had been struck by a hand, fell to the ground and, before succeeded in flying away, it was immediately caught by a T. c. worker. The ant kept a tight hold of the ground and did not let the struggling fly (several hundred times its weight) get away for about 30 sec. The capture carried by the T. c. ant was caught by a much larger L, fuliginosus ant, which took the advantage of its weight and began to drag the trophy together with its previous holder. After a short time the T. c. ant found a support for its legs, stopped the marching, and eventually recovered the prey Some of the anatomical and morphological features of T. c. account for the fact that these small ants are much stronger than at least some of their big cousins. This species has extremely powerful jaws and muscles connecting head and body. These powerful muscles are located in the cranium (15, 20) which in this species is well developed (in relation to body size) by comparison with other species of ants. No satisfactory anatomical explanation has so far been proposed for the strength of the legs. The fact that the same basic pattern of behavior is used to grasp prey or building material suggests that in T.,c. there is no division of labor for these two basic external service functions (building and foraging). This view is supported by our observation that marked ants initially identified as foragers were subsequently observed as builders, and vice versa. However, on account of the above mentioned methodological difficulties, the results we have obtained are not fully convincing regarding quantitative data. It was necessary to verify this assumption with detail- 30G J. DOBRZANSKI and J. DOBRZAmSKA

ed observations of single ants. It was important to study the behavioral attitudes of ants, previously identified as builders, in their recruitment as foragers. In order for that, heavy pieces of prey were placed for forager ants going out of this opening at which large numbers of builders had been previously marked. The forager ants would recruit nestmates to help with the heavy prey; among those helpers, we always noticed the ants formerly identified as builders. They helped in bringing the prey to the nest and were as skillful as other ants in the techniques of carrying prey as well as in locating and following paths. Recruitment was not restricted te the ants formerly engaged in building activities and actually inactively staying in the nest; it was extend- ed to workers actually engaged in building. Moreover it was possible to change the function of an ant from building to foraging by placing a piece of prey near the entrance opening, at which the builders had formerly been marked. Upon encountering a prey the builder, while carrying a piece of sand, would drop its load and carry the newly found trophv to the nest. We did not see in any ant any clumsinness in carrying prey regardless of its weight or size. Only a few individuals did not take the prey and hid in the nest for a long time. Most likely they were young animals, frightened of the strange objects and badly adapted to the outside world. To test if these functional changes were taking place in both direc- tions, we placed large amounts of food near the nest and subsequently destroyed part of the nest at different stages of recruitment and carrying of the prey. The behavior of the recruited workers was completely uni- form, and, independent of the stage of their foraging expedition, they would immediately abandon their original function, i.e., foraging, in order to repair the damaged nest. Once, when the nest was extensively destroyed, all of the forager ants left their prey and started repairing the nest. Only a primary forager made one more return journey to the prey, but soon abondoned it and joined the builders. We did not notice any behavioral differences between ants labelled as builders or foragers, since both were able to build in exactly the same way. So the suggestion of a lack of division of labor into building and foraging, conceived on the ground of the common model of motor behavior, has been confirmed experimentally. This helps to build up the concept of the social organization of T. caespitum. A majority of the potentially active workers remain within the nest for most of the time and leave cnly in case of emergency: recruiting for transportation of food, repairing of the nest or protecting it. This organization resembles that seen in a bee society (23) but has progressed further in the direction of de- specialization. A bee forager must learn the route to perform foraging ETHOLOGICAL STUDIES IN ANTS (I) 307 functions. Since the knowledge of the neighborhood grows in the course of foraging expeditions, the latter function is the last one in the lifetime of the bee. T. c. foragers do not learn the route, so that foraging may be carried out in this species by any worker accustomed to the external en- vironment of the nest. However, the results obtained do not prove a complete lack of division of labor in T. c. The most primitive form of division of labor (e.g., 8, 11, 13, 18) is the division into internal and external services. In order to study this in T. c. we slightly opened the nests of the species and marked the workers that rescued the larvae and pupae. In one experiment we marked 34 workers, 8 of which were spotted on the surface the following days, two carrying prey and three others near some honey that we had put near the nest. In another experiment 14 nurses were marked and followed for 5 days. They were noticed on the surface on 12 occassions, 4 while building and one carrying prey. On the other hand. we never happened to see among dozens of nursing workers an ant initially marked as-involved in external service. It is the more characteristic, that within the nest there were crowds of marked reserve workers all the time. In this light the fact that none of them took up such a biolo- gically important function as nursing, supports the existence of division of labor into internal and external service. The fact that some nurses do perform external functions afterwards does not contradict this assumption. It is known that young workers, that have never been outside the nest for any physiological (12, 18) or psychical reason (14, 17) often take care of offspring independently of their function (14, 18). A first, often lorced, visit to the outside world only accelerates the passage to external service (5, 12). On the other hand. it must be noted that all of the above described facts hold true for the physiological division of labor existing in some species of ants and depending on age. Young representatives of those species act as nurses and when they reach a certain age they are promoted to external service.

SUMMARY 1. The initial basic activities associated with manipulation of the heavy objects, i.e., seizing, lifting and moving them from one place to another, are in T,cuespiturn workers displayed as a constant pattern of ,motor behavior. 2. This pattern is very stable and stereotyped, which argues for its inborn character. 3. The examples of individual differentiation of behavior were noticed in more advanced development of transportation activities, i.e., when

9 - Acta Neurobiologiae Experilnentalis 308 J. DOBRZANSKI and J. DOBRZANSKA

objects were being carried into the nest. These observations lead us to suggest that the latter stages of carrying behavior are acquired by learning. 4. For good orientation in the surrounding territory an ant does not depend exclusively on the olfactory trails. In the vicinity of the nest, where numerous traces cross, it is the memory of general direction that helps finding an individual trace and orientation on the large foraging territory without learning paths to and from the food. 5. In societies of T. c. ants no division of labor exists at least in relation to the basic functions of external service, i.e., building and foraging. Each individual has the inborn ability to carry out these two activities (lifting and carrying a burden and orientation in foraging territory) and does so when required. 6. There are a number of important data speaking in favor of a division of work into internal and external service. This division may be based on age, however this has not been established conclusively, and the possiblity of a permanent division between internal and external services needs to be examined. 7. The lack of division among ants performing external services and the territorial orientation of all ants allow the control of the foraging area without the need to divide the area among the foraging ants. Each ant finds the trail to and from the nest by using the memory of direction and olfactory senses. A well developed recruiting system and the rapid transportation of burden allows the removal of the prey to the nest regardless of its size and weight.

This investigation was supported by Project 09.4.1 of the Polish Academy of Sciences.

REFERENCES ' 1. ARNOLDI, K. W. 1937. Formes of life in ants (in Russian). C. R. Ac. Sci. URSS 16: 343-345. 2. BLUM, M. S. and ROSS, G. N. 1965. Chemical releasers of social behaviour. V. Source, specificity and properties of the odour trail pheromone of Te- tramorium guineense F. J. Insect Phys. ll: 857-868. 3. BRIAN, M. V., ELMES, G. and KELLY, A. F. 1967. Populations of the ant Tetramorium caespitum Latreille. J. ,Anim. Ecol. 36: 337-342. 4. DOBRZA~~SKA,J. 1958. Partition of foraging grounds and modes of convey- ing information among ants. Acta Biol. Exp. 18: 55-67. 5. DOBRZAfiSKA, J. 1959. Studies on the division of labour in ants genus Fob mica. Acta Biol. Exp. 19: 57-81. 6. DOBRZARSKI, J. 1966. Contribution to the ethology of Leptotho~axacervo- rum. Acta Biol. Exp. 26: 71-78. 7. DOBRZARSKI, J. 1971. Manipulatory learning in ants. Acta Neurobiol. Exp. 31: 111-140. ETHOLOGICAL STUDIES IN ANTS (I) 309

8. EHRHARDT, S. 1931. uber Arbeitsteilung bei Myrmica- und Messor-Arten. Zeitschr. Morphol. Okol. Tiere 20: 755-812. 9. ESCHERICH, K. 1917. Die Ameise. Schilderung ihrer Lebensweise. Fr. Viewer u. Sohn, Braunschweig. 348 p. 10. FOREL, A. 1869. Observations sur les moeurs du Solenopsis fugax. Mitt. Schweiz. Entom. Gessll. 3: 105-128. 11. FOREL, A. 1920. Les fourmis de la Suisse. 2nd ed. La Chaux de Fonds. 452 p. 12. GOETSCH, W. 1953. Die Staaten der Ameisen. Second ed. Springer Verlag, Berlin. 152 p. 13. GOETSCH, W. and EISNER, H. 1930. Beitrage zur Biologie kornersammeldner Ameisen. 11. Teil. Morph. u. t)kol. Tiere 16: 371452. 14. HEYDE, K. 1924. Die Eni.wic?clung der psychischen Fahigkeiten bei Ameisen und ihr Verhalten bei abgeanderten biologischen Bedingungen. Biol. Zblt. 44: 623-654. 15. JANET, C. 1899. Essai sur la constitution morphologique de la t&te de l'insecte. Third ed. G. Garre a. C. Naud. Paris. 74 p. 16. JANET, C. 1901. Observations sur les fourmis. (Graines dans les nids de Te- tramoriu,m caespitum et de Lasius). Limoges. 68 p. 17. KIIL, V. 1934. Untersuchungen uber Arbeitsteilung bei Ameisen (F. rufa L.! Camponotus izcrculeaibus L., und C. ligniperda Latr.). Biol. Zblt. 54: 114- 146. 18. LUBBOCK, J. 1929. Ants, bees and wasps. A record of observations on the habits of social Hymenoptera. Paul Hegan. 450 p. 19. MOLITOR, A. 1954. Bemerkungen zur Koloniengrundung der mitteleuro- paischen Ameisen. Verhandl. Zooi.-Botanisch. Gesell. (Wien) 94: 59-68. 20. NASOJSOV, N. V. 1889. Tile materials to natural history of ants. 11. The materials to history of ant Lasius flavus (in Russian). Tr. Labor. Zool. Mus. Mosk. Univ. 4: 120. 21. PETAL, J. 1961. Materialen zcr Kenntnis der Ameisen (Formicidae) der Lub- liner Hochbene (I-IV) (in Polish, German summary). Fragm. Faun. 9: 135-151. 22. RAIGNIER, A. 1952. Vie et rnoeurs des fourmis. Payot, Paris, 224 p. 23. RtiSCH, G. A. 1925. Untersuchungen iiber die Arbeitsteilung im Bienenstaat. Teil I. Z. Vergl. Phyaiol. 2. 571-631. 24. RUZSKIT, M. 1905. The ants of Russia: the taxonomy, geography and data of biology of the Russitin ants (in Russian). Tr. Obshch. Estestvoispytatel'ei' pri Imperat. Kazanskom Univ. (Kazan') 38 (4-6): 1-796. 25. STAGER, R. 1929. Die sammensamelnden Ameisen und das Ernahrungs Prob- lem. Zeitschr. Wiss. Insektenbiol. 24: 199-213. 26. TOROSSIAN, C. 1960. La biologie de la fourmi Dolichoder~~squadripunctatus. Ins. Soc. 7: 383-393. 27. TSUNEKI, K. and ADACHI, Y. 1957. The intra- and interspecific influence relations among nest populations of four species of ants (in Japanese, English summary). Jap. J. Ecol. 7: 166-171. 28. WILSON, E. 0. 1971. The Insect Societies. Belknap Press, Cambridge. 548 p.

Received 17 January 1975

Jan DOBRZAfiSKI and Janina DOBRZARSKA, Department of Neurophysiology, Nencki Institute of Experimental Biology, Pasteura 3, 02-093 Warsaw, Poland.