Despite their mythical portrayal as malevolent bloodsuckers — and a more modern connection with vengeance-minded superheroes — bats on both sides of the planet are fighting for survival against a more banal foe: extreme temperatures.

Rescue workers at the Toronto Wildlife Centre are caring for 68 bats, including a colony from Newmarket that was found freezing to death during the ice storm.

“Every winter, this does happen with some bats; it’s just this is more bats than usual this winter,” said Nathalie Karvonen, the centre’s executive director.

Half a world away, a scorching heat wave in Australia has killed tens of thousands of bats. Experts say there are parallels.

“Small body size is the big factor in both cases,” said Kenneth Welch Jr., who teaches biology at the University of Toronto’s Scarborough campus.

Welch said their diminutive size — the species known as big brown bats, being sheltered at the wildlife centre, weigh a mere 15 grams each — makes the animals very sensitive to changes in their environment.

“When you’re so small, you have a high surface area,” he said. This means bats lose water very quickly in dry air, by exhaling and evaporation off their skin, Welch said.

“The extremes of the environments are putting a lot of stress on an animal that, because of its high metabolic rate and high rate of evaporative water loss, is already living fairly close to the edge of existence.”

In Australia, heat-stressed bats cling to trees and urinate on themselves in a bid to reduce their body temperatures, said Louise Saunders, president of the Queensland animal welfare group Bat Conservation and Rescue. Saunders said at least 50,000 bats had been killed by the heat in the Australian province.

“As they succumb, they just fall in heaps at the base of trees,” Saunders said. “You can have 250 or more — it’s like dripping chocolate — all dying at the base of trees.”

Rescuers in Toronto have had to nurse dehydrated bats back to health with water-filled syringes and live mealworms. “We’re going through mealworms like crazy,” Karvonen said, adding the centre is having more shipped in from California.

Rescue efforts are all the more significant because North American bat populations are in serious decline.

“The population is already weak. It’s hard for them to recover from a big hit like this,” said Jonathan Newman, director of the school of environmental sciences at the University of Guelph.

There are eight populations of bats in Ontario. Newman said it’s a real possibility some may disappear entirely because of various factors, including habitat loss.

One of the biggest threats to North American bats is an invasive fungal disease known as white-nose syndrome. The fungus, which grows on bats as they hibernate, has killed millions of bats in Canada and the United States since it appeared in 2006.

“It’s been a truly devastating disease for bats,” said Doug Campbell, a wildlife pathologist at the Ontario Veterinary College. The Committee on the Status of Endangered Wildlife in Canada has identified three Canadian bat species as endangered because of the disease.

Dwindling bat populations matter because bats play a key role, eating flying insects such as mosquitoes and others that damage plants.

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“When the populations are healthy, they’re a significant control on insect populations,” Newman said.

The wildlife centre bats’ prospects are improving. Staff and volunteers have succeeded in coaxing 18 back into hibernation, Karvonen said.

It’s a delicate process that involves teaching the bats to eat the wriggling mealworms on their own — the bats are used to flying insects — ensuring they reach a healthy weight, and then moving them to a cold room.

“The bats are then monitored daily,” Karvonen said. “They do move around a bit during hibernation, so they have food available and some do eat a bit, even when they are at a lower body temperature.”