Santos, JC and Del-Claro, K.(2009)'Ecology And

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Ecology and behaviour of the weaver ant Camponotus (Myrmobrachys) senex J. C. Santos a; K. Del-Claro a a Instituto de Biologia, Programa de Pós-Graduação em Ecologia e Conservação de Recursos Naturais, Universidade Federal de Uberlândia, Uberlândia, MG, Brazil

Online Publication Date: 01 June 2009

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EcologyTNAH0022-29331464-5262Journal of Natural HistoryHistory, Vol. 1, No. 1, April 2009:and pp. 1–26 behaviour of the weaver ant Camponotus (Myrmobrachys) senex J.C.Journal Santos of Natural and K. HistoryDel-Claro Santos and K. Del-Claro*

Instituto de Biologia, Programa de Pós-Graduação em Ecologia e Conservação de Recursos Naturais. Universidade Federal de Uberlândia, Uberlândia, MG, Brazil

(Received 2 September 2008; final version received 17 March 2009)

Weaver ants use silk produced by their larvae to build their nests. This behaviour is one of the more notable instances of social cooperation in animals; however, there are few studies of Brazilian species. This study investigated the ecology, natural history and behaviour of the weaver ant Camponotus (Myrmobrachys) senex in Brazil and showed that the weaver larvae have a fundamental function in nest building. The nests were always arboreal (one nest/plant), with a round form, beige in colour, and with leaves and shoots adhered to the silk nest. The average size was 34.24 cm and the average weight was 163.87 g; nests contained up to 50,000 individuals and several queens. Fusion and fission of colony parts were observed for C. senex. Worker ants were frequently observed feeding on honeydew, fruits and insects; and defended their territory. We suggest that C. senex larvae could be considered an effective caste, valuable in nest construction. Keywords: behaviour; cerrado; Formicinae; nest; silk

Introduction Weaver ants build their nests with silk produced by their larvae (Hölldobler and Wilson 1977a,b,c, 1990). This type of construction is described as one of the more notable instances of social cooperation in animals (Hölldobler and Wilson 1990). The weaver ants belong to the subfamily Camponotinae and to the genera Oecophylla (Cole and Jones 1948; Way 1954a,b; Hölldobler and Wilson 1977c; Lokkers 1986), Downloaded By: [Del-Claro, K.] At: 14:19 29 May 2009 Polyrhachis (Karawajew 1929; Ofer 1970; Robson and Kohout 2005, 2007), Camponotus (subgenera Karavaievia and Myrmobrachys; Maschwitz et al. 1985; Hölldobler and Wilson 1990; Schremmer 1979a,b) and Dendromyrmex (Weber 1944; Wilson 1981). There is evidence that weaving behaviour also occurs in Dolichoderus sp. (Dolichoderinae), but in this case the silk seems to be produced by workers (Maschwitz et al. 1991). In the Neotropics two species of weaver ants are known: Camponotus (Myrmobrachys) senex Smith 1858 (Yanoviak and Kaspari 2000) and Camponotus (Myrmobrachys) formiciformis Forel 1884. Two subspecies are recog- nized for C. senex: C. senex textor Forel 1899 and C. senex ruficlypeus Emery 1920. These subspecies can be clearly differentiated by the workers’ morphologies and by the colour of the nests (Schremmer 1979a,b). Although C. senex are common in South America, there are few studies of their feeding habits, biology and behavioural ecology (Schremmer 1979a,b). Similarly, des- pite the abundance of Brazilian weaver ants, few studies on these species have been

*Corresponding author. Email: [email protected]

published. Camponotus species are common in the Brazilian “cerrado” and they can benefit plants through predation of herbivores (Del-Claro et al. 1996). The present study describes the structure and weaving behaviour of C. senex in southeastern Brazil and provides general data about their biology, natural history and ecology. It also investigates the possible anti-herbivore action of C. senex on their host plants. Finally, this study manipulates weaver ant colonies experimentally with the intention of understanding the fragmentation processes and possible rearrangement of nests.

Material and methods Study area and sampling The study was performed in four distinct locations in southeastern Brazil, Minas Gerais state: (1) Glória Experimental Farm of Federal University of Uberlândia (UFU), Uberlândia (48°13′ W, 18°52′ S, 850 m above sea level); (2) Marileuza Farm of Call Center©, Uberlândia; (3) Faculty of Sciences of Patrocínio, Patrocínio; and (4) an urban area with mango trees in Uberlândia. Field work was performed between December 1998 and June 2002 in gallery forests and a mango orchard. Gallery forest is the vegetation that accompanies the small rivers and streams of Brazil’s central plateau. The medium height of the arboreal stratum varies between 20 and 30 m, presenting an overlap with the trees of the canopy that supplies arboreal cover from 70 to 95%. The humidity is high all the time (up to 60%), including the driest months of the year (see Ribeiro and Walter 1998). Laboratory observations and experimental tests were conducted in a colony of C. senex that was designated Nest 1; it was collected in August 1999 and later it was introduced into the Experimental Garden of the Biology Institute at UFU. In addition, three colonies (collected in March 1999) were also prepared and their behaviour was investigated using free observation sessions in the Behavioural Ecology and Interactions Laboratory (LECI – UFU). These colonies were maintained in plastic trays (30 × 15 cm), containing red glass test tubes with cotton and water to maintain the moisture levels. In the field and laboratory, the behavioural observations were performed with

Downloaded By: [Del-Claro, K.] At: 14:19 29 May 2009 the naked eye or using a magnifying glass and followed ad libitum sampling methods (sensu Altmann 1974 – “all occurrence sampling”, see also Del-Claro 2004). Three hours of VHS recordings were also made, with observations of the colony’s weaving behaviour. The voucher specimens of C. senex were deposited at the Museum of Zoology of the University of São Paulo and in the Museum of Biodiversity of Cerrado, Federal University of Uberlândia.

Nest structure and demography In the field, C. senex nests were investigated for the following characteristics: (1) host plant species, location in the tree and height in relation to the ground; (2) number of nests by tree and distance between them and with other nests; and (3) distance between the nest and central trunk. The nests were examined in all seasons to cover reproduction and the nuptial flight period (production of males and winged females). Ten nests were collected, dissected and analysed in the laboratory for the following characteristics: nest structure; nest constitution; number of individuals; and nest Journal of Natural History 1425

dimensions and weight. The nest microstructure was also analysed using electron microscopy. To determine the proportion of silk used, the nests were dissected manu- ally, and then the vegetable and silk parts were separated to obtain the relative proportion between their masses. To estimate the nest population, a third of individuals from two nests, including larvae, pupae, workers and reproductive individuals, were counted and the total number of individuals was then estimated.

Activity rhythm and feeding behaviour Preliminary observations revealed that C. senex is preferentially active during daylight. To determine the activity rhythm, Nest 1 was acclimatized in the Experimental Garden and four shifts of observations (08.00–18.00 h) were performed on four different days with similar meteorological conditions (sunny days, temperatures between 20 and 27°C, 65% air humidity) in August 2000. During the first 10 min of each hour, all ants on the external walls of the nest and in shoots up to 1 m away were recorded. Nest 1 was also studied from August 1999 to May 2002; 50 h of behavioural observations (20 min each session following ad libitum rules, sensu Altmann 1974) were performed on the food preferences of this ant species (there was no control of food availability in the study area). Colonies found in the field were also observed for the food items used. Live termites, workers of Armitermes sp. (Isoptera: Termitidae), were offered to ants to estimate the effect of the action of C. senex indirectly on the presence of arthropods (possible herbivores or natural enemies of the ant) in the host plants. The termites were glued, by their backs (see Oliveira et al. 1987; non-toxic white glue – Cascolar© (Henkel LDTA, Itapevi, SP, Brazil), to a branch 1 m distant from the nest. We observed for 30 min if the termites were predated by the ants. This procedure was repeated 20 times; one termite was used each time, with a minimum interval of 1 h between each session. As a control group, the experiment was repeated in the same way in a nearby tree that was not connected by its canopy and that did not contain a weaver-ant nest.

Downloaded By: [Del-Claro, K.] At: 14:19 29 May 2009 Interactions between nests In the first experiment, we isolated three queens from a polygynic colony (n = 12 queens), each one with 15 workers. The groups were designated as colonies “A”, “B” and “C”. Then, each colony was isolated for 3 months in Magnolia, Michelia odorata (Magnoliaceae). A band of non-toxic resin (Tanglefoot© (Tanglefoot Company, Grand Rapids, MI, USA) was applied round the trunk, approximately 20 cm above the soil, to prevent the ants from escaping from the host plant. After the isolation period, all colonies were gathered simultaneously in the same tray (30 × 15 cm), with a 5-cm distance between each one. In a second experiment, we collected two nests of similar sizes (approximately 45.5 cm and 52.9 cm) but about 50 m apart. Those nests were conditioned on the same host plant, with 2 m between them, in the Experimental Garden of UFU. Finally, in a third experiment, two other nests of similar sizes (approximately 21.2 cm and 19.4 cm) were collected from two distinct sites, Fazenda do Glória and Fazenda Marileuza, that were more than 20 km apart. Those nests were acclimatized in the same tree, also at a distance of 2 m from each other, in the Exper- imental Garden of UFU. For the three experiments, all movements, interactions and 1426 J.C. Santos and K. Del-Claro

behaviours of the ants were observed for seven consecutive days (in each case observations were performed during the first 10 min of each hour between 08.00 and 18.00 h).

Results Distribution and nest characterization The C. senex nests were found on trees at heights between 3 and 10 m, with large, oval leaves. The average height of nests was 7.76 ± 2.75 m (mean ± SD, n = 11), the average distance among nests in the field was 46.0 ± 40.8 m (n = 10), and the average distance from the central trunk was 8.52 ± 4.17 m (n = 11). The main host plant found was Mangifera indica L. (Anacardiaceae) in peripheral forest (n = 11) and urban areas (n = 4). We also found ant nests in four forest tree species: Tapirira guianensis Aublet. (Anacardiaceae), Faramea cyanea M. Arg. (Rubiaceae), Licania apetala (E. Mey.) Fritsch. var. apetala (Chrysobalanacea) and Styrax camporum Pohl (Styracaceae). For a complete plant characterization see Lorenzi (2004). We found only one nest per plant, except in two mango trees, which bore 17 and 26 nests, respectively. The nest description was as follows: oval form, beige colouration tending towards brown and with leaves and branches adhering to the silk of the walls (see Figure 1A). However, the young nests or repaired walls were whitish, because of recent silk deposits. The silk changes colour during the first hours and after 2 days has achieved its final colour. Some nests, especially the largest and probably older, bore mosses on Downloaded By: [Del-Claro, K.] At: 14:19 29 May 2009

Figure 1. Nest of weaver ant Camponotus senex in a Brazilian savanna. (A) External aspect of the nest: (1) one of the entrances of the nest, (2) leaf adhered to the external wall of the nest. (B) Sections of the nest showing the internal structure. The arrow shows the leaves and branches used as supports in nest fixation. (C) Details of the nest. The arrow indicates a worker on a wall that is being rebuilt. (D) The arrow shows a worker holding a larva in its jaws. The larva throws silk threads while the worker walks on the nest. Journal of Natural History 1427

the external walls. The nests had several holes with approximate diameters of 2–3 mm, which the ants used to gain access to the outside. The flow of ants was greater in the areas closer to the branches that gave access to the host plant. From a distance, the weaver ants’ nests are similar to the wasp nests of Polybia (Vespidae) that were found in the same place. We also observed the formation of satellite nests that usually comprised one to four leaves interlinked with larval silk. These small nests varied in their distance in relation to the central nest and could be in the same plant or in neighbouring plants. These satellite nests had a constant flow of workers to and from the central nest, and no queen was found inside them. A three-dimensional structure composed of several small chambers connected by passages was found inside the nests. The branches and leaves formed a central skeleton inside the nest, giving the internal support needed for the building of the chambers and walls (Figure 1B,C). Many leaves that were wrapped up for the nest were unable to perform photosynthesis and died. As a result, with time, the suspending branches can break, causing the nest to fall to the ground (recorded on four occasions). More- over, abiotic factors such as wind and rain can also contribute to this process. In all fallen nests, we could not find any living individuals, and in only one case were dead males observed. The nests reached up to 65 cm (34.24 ± 14.44 cm; mean ± SD, n = 12) in their larger diameter and 64 cm (25.77 ± 15.38 cm; n = 12) smaller diameter. The nest mass was approximately 163.87 ± 216.99 g (n = 12) and the proportion of silk used in nest construction varied between 18.40 and 68.50% of the total weight (46.69 ± 15.02%; n = 10). Inside two nests, we observed oval structures that were not identified; their average diameter was 2.6 ± 0.6 cm (n = 50) and each had a unique cylindrical tube 2.1 ± 0.2 cm (n = 50) in length. All structures were constituted by larval ant silk and many were connected outside the nests. Inside, were the remains of exuviae, probably of Lepidoptera. In one nest, 389 structures were counted, internally and superficially.

Nest building behaviour The ants initiated nest building by tying together adjacent leaves, at points of Downloaded By: [Del-Claro, K.] At: 14:19 29 May 2009 minimum distance, with silk liberated by the larvae. The larvae were transported by the workers to the areas for weaving; workers held the larvae with their jaws by the dorsal part of the first third of the body (Figure 1D). We noticed that the workers did not make orderly or sequential movements with the larvae. The movements were random, the worker placed the mouth of the larva on the substratum, the larva then liberated the silk, closing empty spaces or interconnecting leaves and external parts of the nest. At the same time as the worker moved with the larva, it also played with its antennae, touching the back of the larva and touching the substratum alternately. The mechanical touch of the worker’s antennae on the back of the larva seemed to stimulate the liberation of the silk. As the silk wall was being formed, a second group of workers added small particles of animal material (parts of insects and arthropods), vegetable material (parts of leaves and stems, seeds and small pieces of other structures) and debris (Figure 2A–C). Internal or external parts of the nest wall were also removed from their original positions and added as particles in new constructions. After the addition of materials to the silk, the workers moved the larvae over the silk containing debris again, producing an overlap of silk layers. This composition was 1428 J.C. Santos and K. Del-Claro

Figure 2. Scanning Electron Micrography of the nest of the weaver ant Camponotus senex. (A) Part of the nest with a worker. The arrow indicates the wall structure (× 20 magnification). (B) Detail of part of the nest; (1) wall of the nest, (2) layer of silk that belongs to an internal wall (× 30 magnification). (C) Scan of the surface among the silk layers. The arrow shows deformed organic material deposited by ants among the silk layers (× 30 magnification). (D) Scan of the wall of the nest showing the random positioning of the silk threads (× 600 magnification). Downloaded By: [Del-Claro, K.] At: 14:19 29 May 2009 more common in the internal walls of the nest, but some walls only comprised larval silk. Microstructural analysis showed that the threads of silk in the walls appear all reeled and interlaced in a disorganized way, not following any pattern in their disposition (Figure 2A–D).

Nest population We estimated that a small nest of 21-cm diameter had a population of 32,224 ants and a single queen; whereas in a medium-sized nest of 37-cm diameter, we estimated a population of 55,657 ants and 12 queens. The population structure of nests is presented in Table 1. In two other nests, for which the total population was not estimated, there were eight and 30 queens. We observed that queens, eggs, larvae and pupae were always found in the central part of the nest. Satellite nests were small and varied widely in their populations (Table 2). Winged ants, males and females, were observed between the months of September and January, indicating that the reproductive period occurs in the spring, with the Journal of Natural History 1429

Table 1. Demographic data of two nests of Camponotus senex (Formicidae: Formicinae) on mango trees Mangifera indica (Anacardiaceae) in a Brazilian savanna.

Nest size Dimensions (cm) Queens Workers Pupae Larvae Males Total

Small 21 × 10 1 23,845 2578 5800 − 32,224 Medium 37 – 27 12 27,820 9828 8719 11,290 57,657

Table 2. Characterization of satellite nests of Camponotus senex (Formicidae: Formicinae) and their associations with hemipterans in mango tress in a Brazilian savanna; nests collected in May of 2002.

Nests Size (cm) No. of No. of ants Mutualism No. of hemipterans leaves Sp1 Sp2

A 19.7 2 63 + 26 595 B 23 2 107 + 28 227 C 18.5 1 20 + 253 65 D 23.4 1 97 + 128 − E 12.7 3 25 + 65 136 F 23.9 1 335 −−− G 14.4 5 98 + − 61 H 10.9 2 23 + 50 8 I* 24.6 − 613 −−− Mean ± 19.01 ± 5.22 2.00 ± 1.00 153.44 ± 197.50 (+) 91.67 ± 87.36 182 ± 216.02 SD

*Nest on an epiphyte bromeliad (Bromeliaceae) in mango tree.

arrival of the first rains at the end of September. All of the dissected nests contained reproductive forms, males (three nests) or females (three nests); however, we never observed both reproductive castes simultaneously in the same nest. Downloaded By: [Del-Claro, K.] At: 14:19 29 May 2009 Coalition of colonies In the first experiment, after 3 months of isolation, the colonies presented different proportions of workers and silk. Colony “A” contained four workers, pupae, larvae, many eggs and silk. Colony “B” contained four workers, many eggs, but no pupae, larvae or silk. Finally, colony “C” contained one worker, few eggs, no pupae or larvae and little silk. All workers in the three colonies died naturally, for which reason there was a difference between the initial and final numbers of workers. As a result, when the nests were put together in the same tree, there were no negative interactions among the workers of the colonies or even among the queens of the different colonies. All of the eggs of colonies “B” and “C” were transported to colony “A”, and the queen of colony “B” moved simultaneously to colony “A”. There was a total and immediate fusion of colonies “B” and “A”. All this movement occurred in the first 3 h. The following day, the queen of colony “C’ joined the other two, fusing the three colonies definitively. This result indicates that C. senex ants were capable of recognizing each other and of living together again, as occurs in the subdivision of a colony or in 1430 J.C. Santos and K. Del-Claro

the formation of satellite nests, for instance. An additional case proves the results of the first experiment. Direct observations of Nest 1 showed that it was also common in the natural population. Natural migration was observed for a new nest, starting from the construction of a satellite nest in a nearby tree. The new nest was built in a higher part of the tree, to which all of the individuals migrated, abandoning the original colony. The constant shadow of the old nest might have been the main cause of this migration. The second experiment corroborated the results of the first. The colonies, possibly kindred, when joined in the same tree, did not attack each other. Indeed, we observed the transport of pupae, larvae and eggs from one colony to the other. How- ever, there was not a total coalition between the nests. On one occasion, in the field there was a total migration of ants from a fallen nest to a satellite nest that remained on a tree after a strong storm. Finally, in the third experiment, we united two nests from distant areas in the same tree. Results revealed that these colonies, not kindred, attacked each other and disputed the host plant as a territory. During the interaction, the workers bit mutu- ally. At the end of 3 days, one of the colonies was totally abandoned, the surviving ants had probably migrated to another place.

Activity rhythm, foraging and natural enemies Camponotus senex forages mainly on vegetation, especially on the host plant and on the nearby vegetation, but we also observed ants foraging in the soil close to the host plant. The diurnal activity peak was between 10.00 and 13.00 h, and the activity was reduced with proximity to the evening (see Figure 3). However, in spite of being a daytime forager, we believe that C. senex begins nest construction at night because we never witnessed nest expansion during the observation periods, which suggests that they accomplish construction when we were not systematically observing, i.e. between 19.00 and 06.00 h. The following food items were recorded during the observations being collected by C. senex workers: extrafloral nectar, secretions of butterfly caterpillars (Lycaenidae), Downloaded By: [Del-Claro, K.] At: 14:19 29 May 2009

Figure 3. Activity rhythm of Camponotus senex, between 08.00 h and 18.00 h, in a nest maintained in the Experimental Garden, Uberlândia, MG (n = 4 observations). Journal of Natural History 1431

honeydew of hemipterans (Membracidae, Aphididae, Coccidea), fruit secretions (mango) and carrion; the ants also prey on several insects (Diptera, Hymenoptera, Coleoptera, Lepidoptera, Neuroptera) and small arachnids. Moreover, some satellite nests had inside two Hemipteran species (scale insects) assisted by workers (Table 2). Our experimental test of termite attack showed that all of the live termites offered as baits on a host plant were killed and taken to the central nest in less than 5 min. In the neighbouring plants, the control group, the termites were not removed by weaver ants. We believe that the weaver ant C. senex has the potential to reduce the action of herbivores on their host plant. The main natural enemies of C. senex were spiders (Salticidae) and other small ants, like ants of the genera Monomorium and Pheidole. These were seen attacking some colonies (n = 2) and satellite nests (n = 3), mainly in those colonies that fell to the ground. We observed a bee invasion, Apis mellifera, in one nest.

Discussion The preference of C. senex for fruitful trees, large leaves and the highest and sunny parts of the canopy is a pattern observed in other species of weaver ants (Maschwitz et al. 1985). These preferences can be related to the leaf morphology (Way 1954a), availability of food resources (Way 1954a; Way and Khoo 1991) and possibly to the thermoregulation in the nests (Elangovan and Passoupathy 1998). The abundance of weaver ants in agroecosystems can be justified by the existence of good conditions for the establishment of nests in those systems (Way 1954a), such as fruitful trees with favourable architecture, and the low frequency of predators and natural competitors (Way 1954a). As a resuslt of the arboreal nest, the weaver ants are subject constantly to meteorological factors, mainly strong winds that can overthrow and destroy the colony. In this case, the fragmentation of C. senex to satellite nests, as the reproduction for sociotomy (Schremmer 1979a,b), as well as the coalition of sister colonies (Schremmer 1979a,b; Herbers 1993), are fundamental processes that can increase significantly the survivorship chances of a colony. This apparent altruism also can result indirectly in an increase in fitness; consequently, enhancing the survival chances of the genetic Downloaded By: [Del-Claro, K.] At: 14:19 29 May 2009 patrimony and reducing the possibility of a local extinction (see Krebs and Davies 1993). Both characteristics, polygyny and the large number of workers, are important to the occurrence of sociotomy and colony coalition in C. senex. The abundance of ants and the existence of several queens can facilitate the fragmentation, transport and construction of new nests, and minimize the mortality rates caused by physical factors and biological factors such as predators and parasites. The weaving behaviour in C. senex was similar to that found for other weaver ant species of the Camponotus genus (Maschwitz et al. 1985). However, C. senex presented the most elaborate system among all weaver ants, because this species had the large investment in larval silk used in building the nest (e.g. Schremmer, 1979a,b; Hölldobler and Wilson 1990; Robson and Kohout 2005, 2007). The polygyny in C. senex, recently also observed for Oecophylla smaragdina (Peng et al. 1998), is an important attribute for the maintenance of a significant number of larvae and workers, as observed in other weaver ants (Way 1954a; Hölldobler and Wilson 1977c). In C. cenex, other main functions of the workers include the construction of the nests, defence and exploration of territories (see Santos et al. 2005a,b). 1432 J.C. Santos and K. Del-Claro

In ants, especially those of tropical forests and savannas, it is common for animal secretions and vegetables to make up part of their diet (Del-Claro and Oliveira 1999, 2000; Yamamoto and Del-Claro 2008). This feeding behaviour can also be observed in weaver ants, which consume honeydew (Way 1954a,b; Maschwitz et al. 1985; Degen and Gersani 1989; Dorow and Maschwitz 1990), extrafloral nectar (Fuente and Marquis 1999) and the secretions of butterfly caterpillars (Fiedler and Maschwitz 1989; Seufert and Fiedler 1996). Moreover, weaver ants often build pavilions where they raise hemipterans (coccids, aphids and membracids) for their subsistence (Way 1954a,b; Maschwitz et al. 1985; Dorow and Maschwitz 1990). According to Degen et al. (1986), the hemipterans’ honeydew is an important energy resource for the maintenance of colonies of Polyrhachis simplex. The honeydew can be an essential resource that acts as a modulating agent in the tropical arboreal ant communities (Davidson 1997; Del-Claro and Oliveira 2000). Weaver ants, like C. senex, are important predators on trees or in an eventual incursion into the soil (Wojtusiak et al. 1995). This fact is related to the territorial dominance of these ants (Hölldobler and Wilson 1977a,b; Hölldobler, 1979). For this reason, weaver ants are pointed to as potential models for studies as agents of biological control in agroecosystems (Huang and Yang 1987; Way and Khoo 1992; Van Mele and Cuc 2000). Several studies suggest a reduction of herbivores in crop plants, mainly for the genus Oecophylla (Way and Khoo 1991, 1992; Peng et al. 1995; Sporleder and Rapp 1998; Van Mele and Cuc 2000; Van Mele and Van Lenteren 2002; Van Mele 2008). Our data showed that C. senex can remove potential herbivores on trees, so this species has a great potential to be used as biological control agent in mango cultures, as suggested for O. smaragdina (Van Mele and Cuc 2000). C. senex are aggressive ants but that can be manipulated, mainly during the night, enabling also the use of integrated management in pest control. Weaver ant species are typically diurnal; however, some studies also related activity peaks at nightfall and dawn for C. texens and C. gombaki (Maschwitz et al. 1985; Degen and Gersani 1989). According to Degen and Gersani (1989) the daily activity of Polyhachis simplex is affected by climatic factors and seasonal factors. Neverthe- less, activity outside daylight hours had already being registered for Oecophylla (Hemmingsen 1973), which showed active weaving during the night. Here we suggest Downloaded By: [Del-Claro, K.] At: 14:19 29 May 2009 that such activity can also occur in C. senex. This behaviour probably reduces predation, parasitism rates and the direct exposure of larvae to the sunshine, a time of great vulnerability occurring when weaving the external walls of the nest. The Brazilian tropical savanna is a habitat characteristically marked by high annual temperatures (Oliveira and Marquis 2002) and larval dehydration during the day can be accentu- ated. For instance, during the day, larvae of O. smaragdina are subject to the predation of the spider Cosmophasis bitaeniata (Salticidae) during weaving (Allan and Elgar 2001). Small ants, like Pheidole, are competitors and efficient predators of several insects, including other social insects and ants (Hölldobler and Wilson 1990; Howse 1984) and can influence weaver ant populations as O. longinoda (Rapp and Salum 1995) and can possibly interfere negatively also in the populations of C. senex. Weaver ant nests can be partially occupied by bees (Sakagani et al. 1989). Laroca and Almeida (1989) commented that the bee Paratrigona myrmecophyla (Apidae) can live in nests of C. senex. The nest similarity between C. senex and the aggressive wasp Polybia (Vespidae) suggests a potential mimetic relationship, probably conferring mutual benefits on both species against visually oriented vertebrate predators. Journal of Natural History 1433

The strategy of the use of the weaver larval silk represents a key for understanding the evolutionary and phylogenetic processes in arthropods (Craig 1997). As for other weaver ants, we suggest that C. senex larvae could receive the status of caste because of their fundamental role in colony life. Another relevant evolutionary aspect to weaver ants refers to the function of the males in Hymenoptera beyond their sexual function. Laboratory observations and initial analyses of sex ratio in the brood of C. senex, suggest that at least some of the larvae used in the weaving are males (Santos and Del-Claro in preparation). For the genera Oecophylla and Polyrhachis (e.g. Robson and Kohout 2007), this behaviour has been demonstrated (Wilson and Hölldobler 1980; Hölldobler and Wilson 1990). According to Hölldobler and Wilson (1990), cooperation and altruism in male ants are rare and deserve detailed examination.

Acknowledgements We are grateful to the Pós-graduação em Ecologia e Conservação de Recursos Naturais – UFU, Fapemig and CNPq for financial support to J.C. Santos and K. Del-Claro and to E. Tizo-Pedroso and three anonymous referees for critical review of the manuscript.

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