Can temperate insects take the heat? The risks of high temperature exposure to meat ants caused by climate change

1. Insects in temperate regions are predicted to be at low risk of climate change owing to high thermal safety margins (low optimal performance temperature relative to habitat maxima) and/or high warming tolerance (high thermal tolerance relative to habitat maxima) relative to more tropical species. However, these assumptions have been generally poorly examined and such forecasting typically fails to account for microclimatic variation and behavioural optimization of insects.
2. Here, using Iridomyrmex purpureus meat ants from Armidale, NSW, we show that ants regularly forage for short periods (minutes) at soil temperatures well above their upper thermal limits determined over slightly longer periods (hours) and do not show any signs of a classic thermal performance curve in voluntary locomotion across 10-55°C.
3. Generally close associations of ant activity and performance with microclimatic conditions, possibly to maximise foraging times, suggest I. purpureus display highly opportunistic thermal responses and readily adjust behaviour to cope with extremely high trail temperatures. Increasing frequency or duration of high temperatures is therefore likely to result in an immediate reduction in foraging efficiency.
4. These results for a key functional group suggest that (1) soil-dwelling temperate insects may be at higher risks of extinction with increased frequency or duration of high temperatures resulting from climate change than previously thought; and (2) that indices of climate change-related extinction are strongly influenced by the scale of climate metrics employed.