Fears ants could be wiped out by rising temperatures

Ants do not adjust their behaviour in response to soaring temperatures, meaning they may struggle to adapt to the climate crisis, a report has found.

Researchers at North Carolina State University showed that ants persisted in sub-optimal microhabitats even when optimal ones were present.

Ants are ectotherms – animals whose body temperature depends on the environment. While these animals experience a range of temperatures in daily life, most ectotherms prefer habitats that are slightly cooler than the so-called optimal functioning temperature in which they are best able to perform all of life’s functions, the report states.

An ectotherm will die if it encounters an environment warmer than the optimal point. Little is known, however, about how or even if insect ectotherms will adjust their behaviour to avoid warmer but still safe temperature ranges – in which functioning is physiologically possible but not optimal – which are increasingly likely due to global climate change.

“It’s interesting that the worker ants we observed were willing to put themselves in uncomfortable situations while foraging,” said Sara Prado, an adjunct professor and co-author of the study. “I wonder if the food was ‘profitable’ enough for the ants to stretch their comfort levels, or if they are simply willing to sacrifice their wellbeing for the sake of the colony.”

To learn more about how insect species may respond to those warmer sub-lethal temperatures, researchers at the university studied five species of ant common in North Carolina.

The researchers used a unique ant thermometer to measure the temperature of the ants themselves, which varied by ant colour and body size. Secondly, to determine each species’ preferred temperature, the researchers collected some ants for the lab and placed them in a rectangular chamber with a controlled temperature gradient.

The researchers found that the ants in the lab did have distinct thermal preferences, but ants in the field were active in their preferred climates only slightly more often than would be expected to occur by chance. Instead, most species were collected in sites that were warmer than preferred, suggesting a lack of awareness or some limitation in their ability to adjust to increasing temperatures.

“Warmer times and places make warmer ants, and they’re not adjusting their activity to match their preferred conditions,” said Elsa Youngsteadt, a professor of applied ecology at the university and a co-author of the study.

“For now, this may be a trade-off that works out fine for them. But if you think of the huge biomass of ants underfoot, their metabolic rates are all creeping upward as the climate changes.

“Even if it doesn’t kill them outright, what does that amped-up metabolism mean for their life cycle and even the whole forest ecosystem?”