Predatory Behavior in Dominant Arboreal Ant Species: The Case of Crematogaster sp. (Hymenoptera: Formicidae)

Crematogaster sp. is a dominant arboreal ant species that captures and retrieves very large prey. Hunting workers forage collectively thanks to short-range recruitment. They detect prey by contact, then rapidly attack, seizing small prey by the body and large prey by a leg. In this study, almost all the active prey were spread-eagled by several workers, even when small enough to permit a single worker to easily master them. While certain workers spread-eagled the prey, others deposited venom on the prey body using their spatulated sting (topical action of the venom). The well-developed arolia on the pretarsus of workers' legs have crucial importance for the success of prey capture (spread-eagling) and transport in an arboreal habitat. These results are compared with those known for other arboreal-dwelling generalist predator ant species.     

Interactions of the ant Crematogaster scutellaris with the fig/fig wasp mutualism

Abstract. 1. A classical example of specialised pollination mutualisms is the relationship between fig trees and their pollinating wasps, in which each partner depends completely on the other for its reproduction; however the fig/fig wasp association is also the target of a great diversity of other species, ranging from specialised parasites to opportunistic foragers, among them ants.
2. The ant community and the sources of ant attraction observed on the Mediterranean fig tree Ficus carica were characterised.
3. A guild of ants attracted by homopterans tended on the plant was distinguished from a second guild composed of two co-dominant ant species ( Crematogaster scutellaris and Pheidole pallidula ) that prey mostly on pollinating wasps, abundant during certain parts of the fig cycle.
4. Foraging workers of C. scutellaris search for prey on the fig inflorescence (syconium), capturing pollinating wasps mostly at the peak of wasp emergence and at a rate estimated to reach 600 prey per day for an entire tree.
5. Detailed study of the predatory sequences displayed under experimental conditions showed that ant workers captured 100% of the pollinating wasps offered, while they captured only 5.5% of the parasitoid wasp specific to the pollinator. The respective impacts of the interaction on ants and on the figs are discussed, as well as several behavioural traits of predation by the dominant ant on pollinators.     

Paralyzing action from a distance in an arboreal African ant species

Due to their prowess in interspecific competition and ability to catch a wide range of arthropod prey (mostly termites with which they are engaged in an evolutionary arms race), ants are recognized as a good model for studying the chemicals involved in defensive and predatory behaviors. Ants' wide diversity of nesting habits and relationships with plants and prey types implies that these chemicals are also very diverse. Using the African myrmicine ant Crematogaster striatula as our focal species, we adopted a three-pronged research approach. We studied the aggressive and predatory behaviors of the ant workers, conducted bioassays on the effect of their Dufour gland contents on termites, and analyzed these contents. (1) The workers defend themselves or eliminate termites by orienting their abdominal tip toward the opponent, stinger protruded. The chemicals emitted, apparently volatile, trigger the recruitment of nestmates situated in the vicinity and act without the stinger having to come into direct contact with the opponent. Whereas alien ants competing with C. striatula for sugary food sources are repelled by this behavior and retreat further and further away, termites defend their nest whatever the danger. They face down C. striatula workers and end up by rolling onto their backs, their legs batting the air. (2) The bioassays showed that the toxicity of the Dufour gland contents acts in a time-dependent manner, leading to the irreversible paralysis, and, ultimately, death of the termites. (3) Gas chromatography-mass spectrometry analyses showed that the Dufour gland contains a mixture of mono- or polyunsaturated long-chain derivatives, bearing functional groups like oxo-alcohols or oxo-acetates. Electrospray ionization-mass spectrometry showed the presence of a molecule of 1584 Da that might be a large, acetylated alkaloid capable of splitting into smaller molecules that could be responsible for the final degree of venom toxicity.     

The ecology and feeding habits of the arboreal trap-jawed ant Daceton armigerum

Here we show that Daceton armigerum, an arboreal myrmicine ant whose workers are equipped with hypertrophied trap-jaw mandibles, is characterized by a set of unexpected biological traits including colony size, aggressiveness, trophobiosis and hunting behavior. The size of one colony has been evaluated at ca. 952,000 individuals. Intra- and interspecific aggressiveness were tested and an equiprobable null model used to show how D. armigerum colonies react vis-à-vis other arboreal ant species with large colonies; it happens that D. armigerum can share trees with certain of these species. As they hunt by sight, workers occupy their hunting areas only during the daytime, but stay on chemical trails between nests at night so that the center of their home range is occupied 24 hours a day. Workers tend different Hemiptera taxa (i.e., Coccidae, Pseudococcidae, Membracidae and Aethalionidae). Through group-hunting, short-range recruitment and spread-eagling prey, workers can capture a wide range of prey (up to 94.12 times the mean weight of foraging workers).     

Prey capture behavior in an arboreal African ponerine ant

I studied the predatory behavior of Platythyrea conradti, an arboreal ponerine ant, whereas most species in this subfamily are ground-dwelling. The workers, which hunt solitarily only around dusk, are able to capture a wide range of prey, including termites and agile, nocturnal insects as well as diurnal insects that are inactive at that moment of the Nyctemeron, resting on tree branches or under leaves. Prey are captured very rapidly, and the antennal palpation used by ground-dwelling ponerine species is reduced to a simple contact; stinging occurs immediately thereafter. The venom has an instant, violent effect as even large prey (up to 30 times the weight of a worker) never struggled after being stung. Only small prey are not stung. Workers retrieve their prey, even large items, singly. To capture termite workers and soldiers defending their nest entrances, ant workers crouch and fold their antennae backward. In their role as guards, the termites face the crouching ants and end up by rolling onto their backs, their legs batting the air. This is likely due to volatile secretions produced by the ants' mandibular gland. The same behavior is used against competing ants, including territorially-dominant arboreal species that retreat further and further away, so that the P. conradti finally drive them from large, sugary food sources.     

Trophic niche,capture efficiency and venom profiles of six sympatric ant‐eating spider species (Araneae: Zodariidae)

The arms race between specialist predators and their prey has resulted in the evolution of a variety of specific adaptations. In venomous predators, this can include venom composition, particularly if predators are specialized on dangerous prey. Here, we performed an integrative study using six species of highly specialized ant‐eating spiders of the genus Zodarion to investigate their phylogeny, realized trophic niche, efficacy in the capture of various ant species and venom composition. Data on natural diet obtained by next‐generation sequencing and field observations showed that the six Zodarion species exploit different ant species. Their phylogeny, based on mitochondrial and nuclear genes, correlated with the composition of their natural prey, indicating that closely related Zodarion species specialize on similar ant species. Prey‐capture parameters differed among Zodarion species suggesting prey‐specific efficacy. Similarly, the venom profiles of both low and high molecular compounds differed among species. Only the profiles of low molecular compounds were correlated with capture efficacy parameters, suggesting that the venom of Zodarion spiders contains prey‐specific components. Our study suggests that Iberian Zodarion spiders are specialized on particular ant species.     

Hunting strategy of a generalist ant species proposed as a biological control agent against termites

We studied the hunting behaviour of Myrmicaria opaciventris (Hymenoptera: Formicidae) in order to evaluate if it can be used as a biological control agent against the termites that damage sugarcane plantations. Hunting workers foraged in groups and recruited nestmates at short-range when they encountered large termite soldiers or groups of small termite workers. Differences in prey capture concerned the: (1) means of detection (from a distance or by contact); (2) termite body part seized (small termites seized by the body; large termites by an appendage); (3) percentages of prey abandoned; and (4) use of venom. The sting of the workers is spatulated implying a topical application of the venom on the prey. Large termites were stretched by several workers whose adherence to the substrate is facilitated by well-developed arolia and claws on the legs while others spread venom on the body and carved it up. An adaptation to termite capture was noted with a distribution of tasks between the workers which subdued prey, and those which transported it. In the former case, the workers easily eliminated termite soldiers, successively attacked several termite workers and even captured new individuals while holding the first ones captured between their mandibles before retrieving them all at once. The remaining individuals were retrieved by the transporting workers. Given this particularly effective predatory strategy, we concluded that, under certain conditions, M. opaciventris can be used as a biological control agent against termites.     

Mandible strike: the lethal weapon of Odontomachus opaciventris against small prey

In order to study both the hunting efficiency and the flexibility of their predatory behavior, solitary hunters of the trap-jaw ant Odontomachus opaciventris were offered small prey (termites, fruit flies and tenebrionid larvae), presenting different morphological or defensive characteristics. The monomorphic hunters showed a moderately flexible predatory behavior characterized by short capture sequences and a noteworthy efficiency of their mandible strike (76.7-100% of prey retrievals), even when presented with Nasutitermes soldiers. Contrary to most poneromorph ants, antennal palpation of the prey before the attack was always missing, no particular targeted region of the prey's body was preferred, and no 'prudent' posture was ever exhibited. Moreover, stinging was regularly performed on bulky, fast moving fruit flies, very scarcely with sclerotized tenebrionid larvae, but never occurred with Nasutitermes workers or soldiers despite their noxious chemical defense. These results suggest that, whatever the risk linked to potentially dangerous prey, O. opaciventris predatory strategy optimizes venom use giving top priority to the swiftness and strength of the lethal trap-jaw system used by hunters as first strike weapon to subdue rapidly a variety of small prey, ranging from 0.3 to 2 times their own body size and from 0.1 to 2 times their weight. Such risk-prone predatory behavior is likely to be related to the large size of O. opaciventris colonies where the death of a forager might be of lesser vital outcome than in small colony-size species.     

Fragmentation or Transportation: Mode of Large-Prey Retrieval in Arboreal and Ground Nesting Ants

Foraging strategy of ant workers has been studied from several aspects, however, the mode of prey retrieval and factors affecting it have been rarely studied to date, even thought it is an important aspect for understanding ant foraging strategy. We investigated the behavioral response against large prey for 44 ant species of 34 genera belonging to eight subfamilies in Japan, Malaysia and Indonesia. Workers of most arboreal ants cut-up large prey at the site of prey capture, and individual workers retrieve the smaller pieces to the nests. In contrast, in most ground-living species, a group of workers retrieve large prey cooperatively without fragmentation. On the ground, parts of the prey item were often robbed by other ant species during this process, while such interference was rare on trees. The significance of the relation between nest site and mode of prey retrieval is discussed.     

Repellency of callicarpenal and intermedeol against workers of imported fire ants (Hymenoptera: Formicidae)

Callicarpenal and intermedeol are two insect-repellent terpenoids isolated from leaves of American beautyberry (Callicarpa americana L.; Verbenaceae) and Japanese beautyberry (Callicarpa japonica Thunb.). The repellency of these two terpenoids against workers of red imported fire ants, Solenopsis invicta Buren, black imported fire ants, Solenopsis richteri Forel, and a hybrid of these two species was evaluated using digging bioassays. In a multiple choice digging bioassay using two colonies from each species and their hybrid, callicarpenal showed significant repellency at concentration as low as 50 ppm against both red imported fire ant colonies and 6.25 ppm against all black imported fire ant and hybrid colonies. Intermedeol showed significant repellency at concentration as low as 1.50 ppm against both red imported fire ant colonies and 6.25 ppm against all black imported fire ant and hybrid colonies. In total, 15 colonies, five colonies from each species and the hybrid, were tested on callicarpenal and intermedeol at 50 ppm in a two-choice digging bioassay. Both callicarpenal and intermedeol showed repellency against all colonies, and intermedeol showed significantly greater repellency than callicarpenal against both species and their hybrid.     

Extrafloral‐nectaries and interspecific aggressiveness regulate day/night turnover of ant species foraging for nectar on Bionia coriacea

Plants bearing extrafloral nectaries (EFNs) vary the secretion of nectar between day and night, which creates turnover in the composition of interacting ant species. Daily variation in the composition of ant species foraging on vegetation is commonly observed, but its mechanisms are poorly understood. We evaluated the daily variation in nectar availability and interspecific aggressiveness between ants as possible regulatory mechanisms of the turnover in ant–plant interactions. We hypothesized that (i) plants would interact with more ant species during periods of higher secretion of nectar and that (ii) aggressive ant species would compete for nectar, creating a daily turnover of species collecting nectar. We tested this hypothesis by measuring the production of nectar during the day and night and by experimentally removing EFNs of Bionia coriacea (=Camptosema coriaceum) (Nees & Mart.) Benth. (Fabaceae: Faboideae) plants in a Brazilian savanna (Cerrado). We then compared the abundance and composition of ant species between those treatments and during the day. Our results indicate that more ant workers forage on plants during the day, when nectar was sugary, while more ant species forage at night, when aggressiveness between ant species was lower. We also detected a day/night turnover in ant species composition. Ant species foraging for nectar during the day were not the same at night, and this turnover did not occur on plants without EFNs. Both dominant ant species, diurnal Camponotus crassus (Hymenoptera: Formicidae) and nocturnal Camponotus rufipes (Hymenoptera: Formicidae), were the most aggressive species, attacking other ants in their specific periods of forage while also being very aggressive toward each other. However, this aggressiveness did not occur in the absence of nectar, which allowed non‐aggressive nocturnal ant species to forage only during the daytime, disrupting the turnover. We conclude that extrafloral‐nectar presence and interspecific aggressiveness between ants, along with other environmental factors, are important mechanisms creating turnovers in ants foraging on plants.     

Defensiveness of the fire ant, Solenopsis invicta, is increased during colony rafting

Colonies of the fire ant, Solenopsis invicta, can survive flood conditions by forming a raft of ants that floats on the water’s surface until the flood recedes or higher ground is found. Having been forced from the protection of their subterranean nests, rafting colonies are totally exposed and are without retreat. I tested the hypothesis that rafting S. invicta colonies would compensate for their elevated vulnerability by increasing their defensiveness. I measured defensiveness using the amount of venom workers delivered per sting (venom dose), since the repellent effects (i.e., pain and tissue damage) of fire-ant venom are dose-dependent. In the laboratory I assayed colony defensiveness before and after flooding colonies from their nests with water. Colonies were consistently and significantly more defensive while rafting (i.e., each colony’s workers delivered higher venom doses when their colony was rafting than they did when it was assayed pre-flood). The larger venom doses of rafting colonies may reduce their chances of being damaged by encounters with other animals by reducing the duration of such encounters through increased repellency. Encounters with S. invicta during flood conditions have the potential to be unusually dangerous; large concentrations of workers are exposed and available for defense, and they deliver significantly larger venom doses when they sting. Received 29 March 2005; revised 20 June 2005; accepted 24 June 2005.     

The hunting behavior of the African ponerine ant Pachycondyla pachyderma

The hunting behavior of the African ponerine ant Pachycondyla pachyderma, a semi-specialized centipede predator, appears well adapted to this kind of prey and shows a graded complexity according to the difficulty it has in overwhelming prey. Small prey (5-to-8-mm-long termites) were detected by contact and seized by the thorax while larger prey (≥30-mm-long centipedes) were frequently detected from a distance and seized by the anterior-most part of their body. Termites and 30-mm-long lithobiomorph centipedes were not always stung, whereas stinging and even repeated stinging was needed for 50-mm-long geophilomorphs and scolopendromorphs. Moreover, overwhelming wide and heavy scolopendromorphs, which have better defensive abilities, involved the use of additional behaviors allowing the workers to capture them safely: venom spreading, and a peculiar stinging posture, the “fatal embrace”. Here the workers seize scolopendromorphs by an antenna or by one of their first legs, wrap themselves around the prey while maintaining their grip with their mandibles and legs, and slowly inject venom into the prey's ventral surface. Workers retrieve small prey solitarily while, for large geophilomorphs and scolopendromorphs, nestmates can be recruited at short range or even at long range through tandem running.     

Sugary food robbing in ants: a case of temporal cleptobiosis

This study reports new information on interactions between Ectatomma tuberculatum (Ponerinae) and Crematogaster limata parabiotica (Myrmicinae). Workers of these sympatric arboreal ant species forage on the same pioneer trees. Diurnally, Ectatomma preyed on Crematogaster workers that avoided overt aggression by respecting a 'safe distance'. At night, Crematogaster initiated raids within the Ectatomma nests that they apparently left with their abdomen empty, then remained near the nest entrances where they successfully intercepted 75.2% of the returning Ectatomma foragers (N = 322). Certain intercepted workers rapidly resumed their return trip. Others (39.1%) were stopped, explored and licked during a long time by the Crematogaster. Most of them were carrying between their mandibles a droplet of liquid food that was stolen. This relationship, that appears to be a typical case of interspecific cleptobiosis, whose expression varies during the daytime, demonstrates for the first time sugary-food robbing, instead of prey robbing, in ants.     

Plant killing by Neotropical acacia ants: ecology,decision‐making,and head morphology

Mutualistic species often associate with several partners that vary in the benefits provided. In some protective ant–plant mutualisms, ants vary in the extent at which they kill neighboring vegetation. Particularly, in acacia ants (Pseudomyrmex), the area around the host tree that ants keep free from vegetation (“clearings”) vary depending on the species. This study assessed whether interspecific variation in clearing size corresponds to workers biting on plant tissue of different thickness. As expected, workers from species making the largest clearings bit more often on thicker plant tissues than workers from species making smaller clearings. Because head shape affects mandible force, I also assessed whether pruning on thick tissue in mutualistic ant species or being a predator in non‐mutualistic species correlated with broader heads, which yield stronger mandible force. The species with the broader heads were non‐mutualistic predators or mutualistic pruners of thick tissues, which suggest that pruning neighboring vegetation in non‐predatory species demands force even when the ants do not kill prey with their mandibles. The findings reveal that clearing size variation in mutualistic ant partners of plants can also be observed at the level of individual decision‐making processes among workers, and suggest that head morphology could be a trait under selection in protective ant–plant mutualisms. Abstract in Spanish is available with online material.     

Exocrine chemistry of the myrmicine ant Zacryptocerus pusillus (Hymenoptera: Formicidae)

Minor workers of the ant Zacryptocerus pusillus have unusual exocrine secretions in both their mandibular and Dufour glands. The mandibular glands contain a 3:1 mixture of 4-heptanone and 4-heptanol, a mixture found only in the related species Z. varians. The Dufour gland contains a mixture of 13 aldehydes from C9 to C18, not previously encountered in ant secretions. The venom glands gave variable results with only nonanal present consistently.     

红火蚁及其他两种蚂蚁毒腺细菌鉴定与多样性分析(英文)

【目的】本研究旨在分析红火蚁Solenopsis invicta毒腺细菌群落多样性,并与热带火蚁Solenopsis geminata和聚纹双刺猛蚁Diacamma rugosum比较毒腺细菌群落差异。【方法】采用Illumine Hiseq 2500测序平台对红火蚁(工蚁、有翅蚁和蚁后)、热带火蚁(工蚁)及聚纹双刺猛蚁(工蚁)毒腺细菌群落16S rRNA基因V3-V4区测序,基于测序数据进行生物信息学分析。【结果】变形菌门(Proteobacteria)在红火蚁工蚁、有翅蚁和蚁后以及热带火蚁工蚁毒腺中占优势,而厚壁菌门(Firmicutes)在聚纹双刺猛蚁工蚁毒腺中占优势。与红火蚁工蚁和有翅蚁相比,柔壁菌门(Tenericutes)在红火蚁蚁后毒腺中更丰富。广州红火蚁蚁后毒腺中假单胞杆菌Pseudomonas相对丰度显著高于其在有翅蚁及工蚁中的。螺原体Spiroplasma相对丰度在热带火蚁毒腺中显著高于在聚纹双刺猛蚁工蚁毒腺中的。毒腺中细菌多样性分析发现,芽孢杆菌属Bacillus和乳酸杆菌属Lactobacillus在广西红火蚁工蚁中的相对丰度显著高于在广州红火蚁工蚁中的。然而,乳酸杆菌属细菌在聚纹双刺猛蚁工蚁毒腺中的相对丰度显著高于广西的热带火蚁工蚁毒腺中的。【结论】毒腺细菌组成和多样性在3种不同种类蚂蚁工蚁和红火蚁不同品级中存在差异。     

Selection and capture of prey in the African ponerine antPlectroctena minor (Hymenoptera: Formicidae)

Prey selection by Plectroctena minor workers is two-fold. During cafeteria experiments, the workers always selected millipedes, their essential prey, while alternative prey acceptance varied according to the taxa and the situation. Millipedes were seized by the anterior part of their body, stung, and retrieved by single workers that transported them between their legs. They were rarely snapped at, and never abandoned. When P. minor workers were confronted with alternative prey they behaved like generalist species: prey acceptance was inversely correlated to prey size. This was not the case vis-à-vis millipedes that they selected and captured although larger than compared alternative prey. The semi-specialised diet of P. minor permits the colonies to be easily provisioned by a few foraging workers as millipedes are rarely hunted by other predatory arthropods, while alternative prey abound, resulting in low competition pressure in both cases. Different traits characteristic of an adaptation to hunting millipedes were noted and compared with the capture of alternative prey. We also noted the parsimony of the behavioural phases during their capture compared to the capture of alternative prey.     

Differences in Aggressive Behaviors between Two Ant Species Determine the Ecological Consequences of a Facultative Food-for-Protection Mutualism

Ant-hemipteran mutualisms are widespread interactions in terrestrial food webs with far-reaching consequences for arthropod communities. Several hypotheses address the behavioral mechanisms driving the impacts of this mutualism, but relatively few studies have considered multiple ant species simultaneously as well as interspecific and intraspecific variation in ant behavior. In a series of field experiments that manipulated ant diet, this work examines the role of induced behaviors of forest ant species actively engaged in mutualism with Hemiptera. Based on other work in ant mutualisms, we predicted a higher frequency of aggressive behaviors towards prey and competitors by ants in the presence of honeydew-producing Hemiptera. We specifically compared Camponotus chromaoides and Formica neogagates (Formicidae), two abundant species in temperate forests of the northeastern U.S.A. After manipulating ant diet and interactions with sap-feeders experimentally, we observed 494 one-on-one interactions between ants and competitors, ladybird beetles and caterpillar prey. We found that C. chromaoides, exhibited behavioral dominance over F. neogagates, and C. chromaoides was more likely to attack ladybird beetles, competing ants, and caterpillar prey. However, contrary to other work in ant-Hemipteran mutualisms, we observed no evidence that food rewards provided by sap-feeders induced changes in ant behavior for either ant species examined. These results reveal the importance of considering interspecific differences in behavior as a mechanism underlying the ecological impacts of ant-Hemipteran protection mutualisms.     

Toxicity and utilization of chemical weapons: does toxicity and venom utilization contribute to the formation of species communities?

Toxicity and the utilization of venom are essential features in the ecology of many animal species and have been hypothesized to be important factors contributing to the assembly of communities through competitive interactions. Ants of the genus Monomorium utilize a variety of venom compositions, which have been reported to give them a competitive advantage. Here, we investigate two pairs of Monomorium species, which differ in the structural compositions of their venom and their co‐occurrence patterns with the invasive Argentine ant. We looked at the effects of Monomorium venom toxicity, venom utilization, and aggressive physical interactions on Monomorium and Argentine ant survival rates during arena trials. The venom toxicity of the two species co‐occurring with the invasive Argentine ants was found to be significantly higher than the toxicity of the two species which do not. There was no correlation between venom toxicity and Monomorium survival; however, three of the four Monomorium species displayed significant variability in their venom usage which was associated with the number of Argentine ant workers encountered during trials. Average Monomorium mortality varied significantly between species, and in Monomorium smithii and Monomorium antipodum, aggressive interactions with Argentine ants had a significant negative effect on their mortality. Our study demonstrates that different factors and strategies can contribute to the ability of a species to withstand the pressure of a dominant invader at high abundance, and venom chemistry appears to be only one of several strategies utilized.