Arboreal Ants Build Traps to Capture Prey Tiny Ants Construct an Elaborate Ambush to Immobilize and Kill Much Larger Insects
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21.4 brief comms MH 14/4/05 4:37 pm Page 973 brief communications Arboreal ants build traps to capture prey Tiny ants construct an elaborate ambush to immobilize and kill much larger insects. o meet their need for nitrogen in the 31062 Toulouse, France restricted foraging environment pro- e-mail : [email protected] Tvided by their host plants, some arbor- †Department of Animal Biology, University of eal ants deploy group ambush tactics in Illinois at Urbana–Champaign, Urbana, order to capture flying and jumping prey Illinois 61801, USA that might otherwise escape1–4.Here we ‡Laboratoire de Psychologie Sociale de la Cognition show that the ant Allomerus decemarticula- (ESA CNRS 6024), Université Blaise Pascal, tus uses hair from the host plant’s stem, 63037 Clermont-Ferrand, France which it cuts and binds together with a pur- 1. Heil, M. & McKey, D. Annu. Rev. Ecol. Evol. Syst. 34, 425–553 a pose-grown fungal mycelium, to build a (2003). 2. Hölldobler, B. & Wilson E. O. The Ants (Harvard Univ. Press, spongy ‘galleried’ platform for trapping Cambridge, Massachusetts, 1990). much larger insects. Ants beneath the plat- 3. Dejean, A. & Corbara, B. in Arthropods of Tropical Forests. form reach through the holes and immobi- Spatio-temporal Dynamics and Resource Use in the Canopy (eds Basset, Y., Novotny, V., Miller, S. E. & Kitching, R. L.) lize the prey, which is then stretched, 341–347 (Cambridge Univ. Press, Cambridge, UK, 2003). transported and carved up by a swarm of 4. Morais, H. C. Insectes Soc. 41, 339–342 (1994). b nestmates. To our knowledge, the collective 5. Benson, W. W. in Amazonia (eds Prance, G. & Lovejoy, T. E.) 239–266 (Pergamon, New York, 1985). creation of a trap as a predatory strategy has 6. Offenberg, J. Behav. Ecol. Sociobiol. 49, 304–310 (2001). not been described before in ants. 7. van Borm, S., Buschinger, A., Boomsma, J. J. & Billen, J. Allomerus decemarticulatus (Myrmicinae) Proc. R. Soc. Lond. B 269, 2023–2027 (2002). is specifically associated with the Amazonian 8. Davidson, D. W. Biol. J. Linn. Soc. 61, 153–181 (1997). Supplementary information accompanies this communication on ant-plant Hirtella physophora (Chrysobal- c Nature’s website. anaceae), which houses colonies in leaf Competing financial interests: declared none. pouches. Workers build galleried structures on their host plant’s stems in which they pierce numerous holes that are slightly larger in Predation diameter than their heads, allowing them to enter and exit5 (Fig. 1a). First, they cut plant Prey plumage adaptation hairs (trichomes) along the stems, clearing a d against falcon attack path. Then, using uncut trichomes as pillars, they build the gallery’s vault by binding cut Figure 1 Galleried platforms built by Allomerus workers act as everal plumage types are found in feral trichomes together with a compound that traps for prey. a, Base of the lamina of two Hirtella physophora pigeons (Columba livia), but one type they regurgitate (for details, see supplemen- leaves: the pouches serve as ant nests, which are interconnected Simparts a clear survival advantage tary information). Later, this structure is by a gallery pierced with numerous holes. b, Start of the capture during attacks by the swiftest of all predators reinforced by the mycelium of a complex of of a locust. c, One hour later, recruited workers have left the — the peregrine falcon (Falco peregrinus)1,2. sooty-mould species that has been manipu- gallery in order to bite, sting and stretch the prey. d, Completion of Here we use quantitative field observations lated by the ants.Fungal growth starts around a cricket capture. and experiments to demonstrate both the the holes and then spreads rapidly to the rest selective nature of the falcon’s choice of of the structure. the prey is progressively stretched against the prey and the effect of plumage coloration We noted that the stems of 34 young gallery and swarms of workers can sting it on the survival of feral pigeons. This seedlings, which had not yet developed leaf (Fig. 1b–d). The ants then slide the prey plumage colour is an independently herita- pouches, did not bear fungus; nine saplings over the top of the gallery — again moving in ble trait3 that is likely to be an antipredator raised in a greenhouse in the absence of and out of holes, but this time in the same adaptation against high-speed attacks in Allomerus developed leaf pouches but never direction. They move it slowly towards a leaf open air space. bore fungus. However, 15 saplings raised in pouch,where they carve it up. The polymorphic feral pigeon is ideal for the presence of ants bore mycelia, whose Because the requirement for protein is investigating the effects of different plumage development was limited to the galleries. crucial,some arboreal ants consume parts of combinations on predator success. One When we eliminated the associated ants the Hemiptera that they attend6, others rely plumage phenotype –– known as the ‘wild’ from five of the 15,the fungus on the galleries on microsymbionts to recycle nitrogen7, and variant — is blue-grey but has a white rump grew into a disorganized structure,and none some have a thin cuticle and non-proteina- between the base of the tail and the lower of the nine new stems that developed bore ceous venom that economizes on nitrogen back, closely resembling the feral pigeon’s any fungus at all. use8.Nevertheless, most of them must cap- rock-dove ancestor3,4 (Fig. 1); all other Because prey seemed to be immobilized ture prey that land on their host plant3.Given plumage types lack this contrasting rump on the top surface of these galleries,we inves- this constraint, the tiny A. decemarticulatus patch3.We tested whether the wild colo- tigated whether these structures could be workers have developed a tripartite associa- ration might impart a selective advantage acting as a trap. Our observations revealed tion with their host plant and a fungus col- over other plumage types during high-speed that Allomerus workers hide in the galleries lectively to ambush their prey. diving attacks by falcons, which often exceed ǁ with their heads just under the holes, Alain Dejean*, Pascal Jean Solano*, 157ms 1 (ref.2;Fig.1a). mandibles wide open, seemingly waiting for Julien Ayroles†, Bruno Corbara‡, During a seven-year period, we recorded an insect to land.To kill the insect,they grasp Jérôme Orivel* 1,485 attacks by five adult peregrine falcons its free legs, antennae or wings, and move in *Laboratoire d’Évolution et Diversité Biologique on free-ranging flocks of feral pigeons in and out of holes in opposite directions until (UMR CNRS 5174), Université Toulouse III, Davis, California, during their daily linear NATURE | VOL 434 | 21 APRIL 2005 | www.nature.com/nature 973 © 2005 Nature Publishing Group.