A lethal disease blamed for virtually reducing entire bat colonies to piles of bones in the United States has arrived in Canada, having crept into Ontario grottoes.

Scientists estimate the mysterious illness, called white-nose syndrome, has killed more than a million bats across the U.S. northeast in just three or four years.

Now, more than 20 cases of the disease have been confirmed at three sites in Ontario, where some fear that shrinking populations of the insect-eating critters could one day have economic implications.

“(It’s) still a small number of bats, especially when you compare it to the amount of mortality that they’re seeing in the United States — you know, hundreds of thousands of bats,” said John Dungavell, a wildlife health policy adviser for Ontario’s Natural Resources Ministry.

“We’re definitely not seeing that here, yet.”

White-nose syndrome has infected hibernating bats across 11 American states, where ailing critters, and even the dead, often look like their muzzles and other parts of their bodies have been dusted with flour.

The dying bats are often found unusually far from the safety of caves and deserted mines in the middle of winter.

There is no evidence white nose is harmful to humans.

None of the Canadian bat species threatened by the disease is considered at risk of extinction.

But losing significant numbers of the bug-munching creatures, which occupy critical roles at the top of a food chain, could affect agricultural and forestry businesses.

In a single night, some bats can devour their own body weight worth of insects, including crop- and tree-damaging pests, like beetles and caterpillars.

“If you saw a tremendous decline in the bat population, like what they’re seeing in the States, you could see increases in mosquito and moth populations and other insects that are sort of considered pests to agriculture,” Dungavell said Tuesday from Peterborough, Ont.

“It’s a very new phenomenon, but something that we take very seriously.”

Since the discovery of the disease four years ago, Canadian biologists had feared bats would carry it across the border from hibernating sites.

“Based on how quickly it spread (in the U.S.), and where it has spread to date, the findings aren’t unexpected but they aren’t good,” Dungavell said.

The illness was first discovered in February 2006 in Albany, N.Y., but U.S. wildlife officials only realized the depth of its impact when they started checking hibernation sites a year later.

At one site in Dorset, Vt., dubbed the “cave of death,” white-nose syndrome has caused 200,000 to 300,000 deaths, or a 95 per cent mortality rate, said Susi von Oettingen of the U.S. Fish and Wildlife Service.

Most of the bats likely died after leaving the cave, but tens of thousands of bodies were still found inside.

“The bones are inches deep,” von Oettingen said. “That’s just one site.”

The Ontario cases of white-nose syndrome were discovered near the towns of Bancroft, Flesherton and Kirkland Lake, not far from Quebec.

Authorities in Quebec, also bordered by the heavily hit states of New York, Vermont and New Hampshire, continue to search for signs of the sickness.

American authorities believe it’s only a matter of time before white-nose syndrome slips into the province.

“It hasn’t turned up (in Quebec) yet, but I wouldn’t say it’s not there,” von Oettingen said.

“It’s spreading as fast as we can get out there and find it.”

Scientists have scrambled to find a way to stop white-nose syndrome but, without any breakthroughs, much of the work to date has involved documenting its staggering body count.

Wildlife experts have been experimenting with treatments for the bat caves, but there are many concerns over what impacts those could have on other flora and fauna found in the grottoes, said von Oettingen.

“To do something about it is going to be incredibly challenging,” she said.

Bat experts say the advance of the disease, now found in a swath of the United States from New Hampshire to Tennessee, doesn’t appear to be slowing down.

“It’s leaving a wake of destruction,” said Paul Cryan, a bat ecologist with the United States Geological Survey.

“It’s with regret that we hear this news (that it has reached Canada) because the places where white nose has been seen, it’s been a pretty hopeless situation.

“We were hoping, for whatever reason, that Canada would be spared.”