Nocturnal ants 'not afraid of winter'
The bulldog ants are affected only by sunset time and leave their nests regularly during twilight.
Image: mccphoto/iStockphoto

Nocturnal bulldog ants are not daunted by low temperatures or neighbouring ants, adopting a clockwork-like hunting schedule throughout the year, a new study reveals.

Research conducted by The Vision Centre and The Australian National University shows that the nocturnal insects’ activity times are not influenced by seasons, temperature tolerance or competition with their neighbours, but by sunset time.

“Our previous observations had shown that different species of bulldog and jack jumper ants (Myrmecia), while living in the same environment, have mutually exclusive hunting times – daylight and twilight,” says Piyankarie Jayatilaka, a PhD student who led the study. “In this study, we wanted to identify if thermal biology restricts their foraging schedules.

“We discovered that ants are active at different times because they are affected by different factors – the day-active ants tune their body clocks to temperature, while night-active ants are affected by sunset time.”

The researchers did a year-round observation of when the ants begin to hunt. They found that the nocturnal – bulldog – ants are affected only by sunset time and leave their nest regularly during twilight.

Diurnal ants – ‘jack jumpers’ – on the other hand, adapt their schedules to moderate temperatures. On extremely hot summer days they are active early in the morning, take a break during the hottest part of the day and become active once again in the late afternoon. On cool summer days they remain active the entire day. When temperatures drop below 10° Celsius, especially in winter, these ants cease activity.

“This is because the daytime ants are more temperature-sensitive, whereas the nocturnal ones have a better tolerance of low temperatures, allowing them to hunt in cold winter nights,” Ms Jayatilaka says. “In our year-long study, the nocturnal ants only took two days off, when the surface temperature at sunset dropped below 5° Celsius.”

The researchers also confirmed that competition does not influence the activity times of these ants.

“The nocturnal ants have a temperature tolerance from 8-40° Celsius, which means they can be active during the day,” says Ms Jayatilaka. “If competition were to influence the ants’ hunting times, these ants would forage during daytime when the diurnal ones hibernate.

“However, the foraging schedule of nocturnal ants in winter remained exclusively to twilight, which means that competition, at least from their day-active relatives, is not a factor.”

Apart from light intensity, she says that further reasons, such as other ants, predation pressure from diurnal animals or visual limitations may cause the nocturnal ants to adopt these particular hunting times.

The study “Different effects of temperature on the foraging activity schedules in sympatric Myrmecia ants” by Piyankarie Jayatilaka, Ajay Narendra, Samuel F Reid, Paul Cooper and Jochen Zeil was published in The Journal of Experimental Biology last week, accessible at

Editor's Note: Please refer to The VIsion Centre for more information.