Nest Architecture of
Bombus transversalis (Amazonian Bumble Bee)
| These video clips give a tiny snapshot of some of the fascinating behavior of this unusual bumble bee, living in the lowland tropical rain forests of Amazonia. I have studied this bee on and off since 1995, after first discovering its unusual leaf-cutting behavior in the Tambopata region of Peru. These first observations of the behavior of this bee suggested that some of the workers were clearing trails (several meters long, radiating out from the nest itself) on the forest floor and that these trails were being actively maintained. Workers found along the trails were the same marked individuals seen over several days of study, suggesting that only certain of the workers used or cleared the trails. For a description of these initial observations see Cameron and Whitfield, 1996; Cameron et al. 1999. |
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A second series of studies made in 2000, examining 15 colonies throughout different regions of the Amazon Basin, including Colombia, Brasil, Ecuador, and Peru, showed that the leaf clearing behavior of this species is quite variable (Taylor and Cameron 2003). None of the colonies in 2000 exhibited trails of the same fashion as those observed in 1995. Instead, the workers cleared leaf litter around the nest in a pattern of broad patches. In one young colony workers were seen leaving and returning from the nest canopy in tandem, over distances of 1-2 m, moving along specific pathways, but the paths had not been fully cleared so it was difficult to know if these would have become linear trails sensu those seen in the 1995 colony.Pushing leaves back toward the nest canopy can occur cooperatively, depending on the stage of nest development, particularly noticeable in a young nest |
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doing lots of leaf cutting; an old nest does not require a large task force devoted to leaf cutting and nest construction. Nonetheless, the leafy canopy must be maintained as critical insulation against the daily torrential rains during the wet season (Taylor and Cameron 2003) and protection from army ant invasion (Cameron et al 1999; Ramirez and Cameron 2003). Such maintenance requires that the external leafy layer be "fluffed up" by workers devoted to that task. In one case, a nest canopy known to be at least 3 years old (although the colony beneath was young) reached enormous dimensions-approx 2m long x > 1m wide. One or more workers were always seen outside the nest engaged in scraping and fluffing the leafy matrix. To the touch a sturdy canopy is spongey; inside the thick, fluffy external layer the leaves are dry and the nest is without mold. A poorly maintained nest is damp and moldy on the inside. |
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| Much is still to be learned about these tropical bumble bees, and their closest relatives, B. pullatus from Central America, and B. atratus, farther to the south. One especially interesting question is whether the tropical bumble bees, which can form unusually large colonies (1,000-3,000 individuals), show aspects of behavior similar to the highly eusocial stingless bees and honey bees. In particular we are interested in whether they have a more complex forager recruitment system than the temperate bumble bees. Dornhaus and Cameron (2003) made an initial study of B. transversalis. |
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