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Sydney, Feb 4 - Bull ants wait for twilight before they start foraging for food, instead of just relying on body clocks or temperature, probably to evade potential predators, a new study says.
Led by Ajay Narendra of The Vision Centre at the Australian National University -, the study shows that instead of relying on circadian rhythms, the bull ant Myrmecia pyriformis keeps a close eye on ambient light levels to forage.
'While bull ants have a circadian rhythm which is based on sunset and sunrise, our study has shown that the time that they go out foraging is based on a specific ambient light intensity,' said Narendra.
'Foraging onset occurs later when light intensities at sunset are brighter than normal, or earlier when light at sunset is darker than normal,' he added.
'We also found different activity rhythms in nests under clear skies and overcast conditions, but the defining characteristic is that it all happens during twilight,' he said.
Bull ants probably wait for twilight to go out looking for food so that they would be less of a target to potential predators, Narendra added.
'So twilight, where limited light is present but where protection against predators is also available, seems to be an ideal time window to begin activity,' he said.
The team conducted the research by bathing Canberra ants' nests with diffused electric lighting and replicating the reducing light of the onset of twilight at a slightly different time of day, said an ANU release.
The researchers say the findings could lead to greater understanding about the cues animals use to begin or stop activity each day.
The findings were published in the Proceedings of The Royal Society B.
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