page_title: Nepenthes bicalcarata
section_title: Association with ants and pitcher infauna
hierarchical_section_title: Nepenthes bicalcarata / Association with ants and pitcher infauna
caption_attribution_description: Nepenthes bicalcarata intermediate pitcher.
context_page_description: Nepenthes bicalcarata, also known as the fanged pitcher-plant, is a tropical pitcher plant endemic to northwestern Borneo, Indonesia. It is a myrmecophyte noted for its mutualistic association with a species of ant, Camponotus schmitzi. As an ant-fed plant it lacks many of the features that characterise the carnivorous syndrome in Nepenthes, including viscoelastic and highly acidic pitcher fluid, the waxy zone of the pitcher interior, and possibly even functional digestive enzymes.
context_section_description: Nepenthes bicalcarata plays host to an unusual species of ant that makes its nest in the plant's hollow tendrils. Described as Camponotus schmitzi in 1933, it is a member of the extremely populous and widespread genus of carpenter ants.
  This unique animal–plant interaction was noted by Frederick William Burbidge as early as 1880. In 1904, Odoardo Beccari suggested that the ants feed on insects found on and around the plant, but may fall prey to it themselves. In 1990, B. Hölldobler and E. O. Wilson proposed that N. bicalcarata and C. schmitzi form a mutually beneficial association. At the time, however, no experimental data existed to support such a hypothesis. A series of observations and experiments carried out in Brunei by Charles Clarke (published in 1992 and 1998), and by Clarke and Roger Kitching (1993 and 1995), strongly support the mutualism theory.
  Nepenthes bicalcarata is a myrmecotroph (ant-fed plant), obtaining nutrients from C. schmitzi in the form of egesta and, occasionally, ant remains. It has been estimated that this input accounts for 42% of the plant's total foliar nitrogen (76% in plants with ant occupancy rates above 75%). The ants increase nutrient retention in the pitchers by preying on infaunal flies, which would otherwise eventually leave their hosts and thereby act as kleptoparasites. This nutrients later becomes available to the plant through the ants' waste. Camponotus schmitzi has also been observed to attack newly caught insects and therefore prevent prey escape. At other times, the ants are very passive, remaining hidden under the inner peristome fold, presumably so as not to dissuade visitation by potential prey species. This behaviour is in stark contrast to other myrmecophytic ants, which are typically highly territorial. John Thompson has suggested that N. bicalcarata may be the only plant species that obtains nutrients through both insect capture and ant-hosting habits.
  Camponotus schmitzi is able to swim in the pitcher fluid using tripod-like leg coordination similar to that of terrestrial locomotion and can remain submerged for up to 30 seconds. When feeding, it appears to target large prey items only, cooperatively retrieving them from the fluid. Hauling food from the pitcher fluid to the peristome—a distance of no more than 5 cm—may take up to 12 hours. In this way the contents of N. bicalcarata pitchers is controlled such that organic matter does not accumulate to the point of putrefaction, which could lead to the demise of pitcher infauna (which may also benefit the plant) and sometimes the pitcher itself.
  The ants have been observed to clean the peristome of fungal hyphae and other contaminants, thereby maintaining high trapping efficiency over the pitcher's lifespan. Research conducted by Dennis and Marlis Merbach has shown that C. schmitzi also benefits N. bicalcarata by protecting it from pitcher-destroying weevils of the genus Alcidodes. In order to create a favourable environment for its pitcher inhabitants, it appears that N. bicalcarata actively maintains the pH of its pitcher fluid at a less acidic level than that found in most other Nepenthes species (this might explain the occasional presence of tree frog eggs in its pitchers). In doing so, however, the plant reduces its ability to digest and assimilate nutrients from captured prey. The pitcher fluid of N. bicalcarata is also less viscoelastic than that of most Nepenthes species, and appears to lack functional digestive enzymes. Nepenthes bicalcarata is therefore highly reliant on its ant symbiont. Indeed, plants not inhabited by C. schmitzi do not appear to benefit significantly from carnivory, with any gains from prey digestion being offset by the high costs of pitcher construction. Conversely, ant-inhabited plants have more leaves and a greater total leaf area, and ant presence is associated with lower pitcher abortion rates and more voluminous pitchers (and consequently greater prey biomass). Studies have shown that plants colonised by C. schmitzi have more nitrogen available to them, and a higher proportion of it 
caption: Intermediate pitcher with swollen tendril colonised by Camponotus schmitzi.
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