According to a recent study by the University of Brunei Darussalam, these tiny bats, native to Borneo, have selected a specific type of carnivorous pitcher plant (Nepenthes raffleslana elongate) as their ideal roost. There is just enough space for them to hang above the bottom of the pitcher plant’s tube, the entry point for the insects it consumes.
From the bat’s point of view, the pitcher plant offers a comfortable, secure place to sleep during the day; but, more than this, it also offers protection from biting insects, specifically blood sucking ectoparasites which are common to most bat roosts.
Just below where the bats hang, at the tube end, digestive fluid prepares the insects for transformation into plant food. There’s enough space in the plant that even pairs of bats can be found roosting together inside the same specimen.
Interestingly, the bat pays rent in the form of its faeces, a rare example in nature of an animal directly feeding a particular plant with nutrients rather than the other way round. The University of Brunei Darussalam study actually started out by trying to understand where these pitcher plants were getting their nutrients, particularly nitrogen, in the nutrient-poor swamp and heath forest where they’re located.
At the same time, it seems likely that this species of pitcher plant has specifically evolved to accommodate the bats. Pointers to this are the unusually low amount of digestive fluid – something harmful for bats to touch – and the tapering form of the plant which makes adequate space for these small bats to spread their wings.