White-Nose Syndrome and Ontario's Bats

White-nose syndrome is a deadly disease of hibernating bats caused by the fungus Pseudogymnoascus destructans. Since reaching Ontario around 2010, it has killed more than 90% of some little brown bat colonies. It cannot infect people or pets. Because of these losses, several Ontario bats are now legally protected, which is exactly why humane, correctly-timed exclusion matters.

If you have bats in your attic, you may be worried about two very different things at once: getting them out of your home, and not doing something harmful or illegal in the process. This guide explains what white-nose syndrome is, how it spreads, why it changed the rules for how bats can be removed in Ontario, and how humane exclusion actually fits into keeping these animals alive.

What is white-nose syndrome?

White-nose syndrome (WNS) is a disease that affects bats while they hibernate. It is caused by a cold-loving fungus with the scientific name Pseudogymnoascus destructans, sometimes shortened to Pd. The fungus grows on a bat’s skin during the long winter hibernation, often showing up as a fuzzy white growth on the muzzle, ears, and wings. That white “nose” is where the disease gets its name.

The fungus does more than look unpleasant. It irritates the bat and disturbs its hibernation, causing it to wake up far more often than it should during winter. Every time a bat wakes, it burns precious fat reserves. Bats that should be sleeping through the cold instead run out of energy, leave the roost too early, and die of starvation or exposure before spring.

WNS first appeared in North America in New York in 2006 and spread quickly. It reached Ontario around 2010 and has since moved across much of the province, including the caves and old mines where our local bats hibernate.

How does white-nose syndrome spread?

The fungus spreads in two main ways, and understanding both explains why it moved through Ontario so fast.

The first is bat to bat. In fall, bats from a wide area gather at the same caves and abandoned mines to hibernate, sometimes packed tightly together in the thousands. When infected bats brush up against healthy ones, the fungal spores pass easily from body to body. Bats also carry the spores with them when they move between winter sites, seeding the fungus into new hibernation spots.

The second way is us. Pd spores can cling to boots, clothing, ropes, and caving gear. A person who explores an infected cave and then visits a clean one can carry the fungus along without ever knowing it. This is why cavers and researchers now follow strict decontamination steps, and why several sensitive sites have been closed to the public. For a homeowner, the practical point is simple: the fungus that is devastating these bats travels invisibly, and once it reaches a hibernation site, the local colony is usually next.

How badly has it hit Ontario’s bats?

The losses have been staggering. Three of Ontario’s bat species that hibernate in caves and mines have been hit hardest:

• Little brown bat — once one of the most common bats in Ontario, with some colonies collapsing by more than 90%.
• Northern long-eared bat — declines so severe it is now considered one of the most at-risk mammals in the province.
• Tri-colored bat — a smaller, less common species also devastated by the fungus.

These are not small dips. In many hibernation sites, bats that once numbered in the thousands were reduced to a handful within just a few years. The rocky landscape along the Niagara Escarpment, which runs right through Grey and Bruce counties, holds caves and crevices that once sheltered large hibernating colonies, and sites like these across our service area have seen the same steep declines documented elsewhere in the province.

If you want to know which species is most likely living in your home, our guide on big brown vs little brown bats breaks down how to tell them apart. The little brown bat, one of the two you are most likely to find in a Grey Bruce Simcoe attic, is one of the hardest hit by WNS.

Why are Ontario bats now protected?

Because of these collapses, the little brown bat, northern long-eared bat, and tri-colored bat are all listed as endangered under Ontario’s Endangered Species Act, and they are protected federally as well. That legal status changes what you are and are not allowed to do when bats move into your home.

You cannot legally harm or poison these bats, and you cannot destroy an active maternity roost. What you can do is use humane exclusion to keep them out of your living space. For a fuller picture of the rules, see our plain-language explainer on whether bats are protected in Ontario.

This is the key point for homeowners: the law does not force you to live with bats. It simply requires that they be removed the humane, legal way — not harmed or trapped.

Can I catch white-nose syndrome from bats?

No, and it helps to understand why. Pd is a cold-loving fungus. It only grows within a narrow, chilly temperature range, roughly the 4 to 15 degree conditions of a winter hibernation site. The human body, at about 37 degrees, is simply far too warm for the fungus to take hold. That is why WNS infects hibernating bats and nothing else: not people, not pets, not other wildlife. You will not catch it from bats in your attic, from bat droppings, or from touching a surface a bat has been on.

That said, bats can carry separate health concerns that have nothing to do with WNS. A small number carry rabies, and old accumulations of droppings (guano) can, in the right conditions, harbour a fungus linked to a lung infection called histoplasmosis. These are real but manageable risks. If you or a pet ever has direct contact with a bat, or you wake to find one in a room where someone was sleeping, contact Health811 or your local public health unit for rabies guidance. Never handle a bat with bare hands.

The takeaway: WNS is a bat disease, not a human one. Your health concern around bats is about safe handling and cleanup, not about the fungus.

Why bats are worth protecting

It is easy to see a bat in the attic as nothing but a nuisance, but these animals earn their keep. A single little brown bat can eat hundreds of insects in one night, and a colony works through many thousands. Across our service area, that appetite quietly benefits the people who live here.

For farmers around Walkerton, Hanover, and the fields of Huron County, bats reduce the number of moths and beetles whose larvae damage crops, easing the pressure that would otherwise be handled with sprays. For cottagers along the shores near Port Elgin, Sauble Beach, and Georgian Bay, bats knock down the mosquitoes and biting insects that make a summer evening on the dock miserable. This is the hidden cost of the WNS collapse: fewer bats means more insects, season after season. Keeping the surviving colonies alive is not only good for the bats. It is good for the whole region.

Does removing bats from my house hurt conservation?

Given how much bats do for us, it is fair to worry that evicting them makes the problem worse. Done properly, it does the opposite.

Humane exclusion does not kill a single bat. It uses one-way doors that let bats crawl out to feed at dusk but block them from getting back in. Once the colony has left, we seal the gaps for good. The bats are alive and free the entire time. Nothing is trapped, harmed, or poisoned.

Where conservation really benefits is what comes next. Because these species are already so reduced, every surviving bat matters. A colony forced out with nowhere to go will scramble to squeeze into the next attic down the road, adding stress and risk. Pairing exclusion with a nearby bat house gives that displaced colony a warm, purpose-built place to settle instead. Our guide to bat houses after exclusion walks through how to position and mount one so your local bats keep eating insects all night, just not inside your walls.

So you are not the enemy of bats by wanting them out of your bedroom. Humane exclusion plus an optional bat house is genuinely good for both you and the colony.

Why does the timing of exclusion matter so much?

Timing is where good intentions can go wrong, and the reason is biology. From roughly May into early August, female bats gather in maternity colonies to give birth. A mother bat usually has just one pup a year, and that pup cannot fly for several weeks after birth. During that stretch it depends entirely on its mother returning to nurse it.

If one-way doors go up during this window, the adult females leave to feed at dusk and find themselves locked out, while their flightless pups remain sealed inside with no way to follow. The result is heartbreaking and, for protected species, illegal. It is also the single most common mistake made by well-meaning homeowners who try to handle bats themselves in early summer.

For this reason, the practical exclusion window in Ontario runs from about mid-August through October, once the pups are flying on their own but before bats settle in to hibernate. Our detailed breakdown of maternity season and why timing matters explains the calendar in full.

Here is a simple way to see it:

Season	Rough dates	What’s happening	Can we exclude?
Maternity season	May – early August	Flightless pups in the roost	No — book and hold a spot
Exclusion window	Mid-August – October	Pups now flying, bats active	Yes — ideal time
Winter	November – April	Bats hibernating elsewhere	Inspect and plan

If you find bats during maternity season, the right move is not to wait and hope. It is to book a free inspection now and hold your place in line for the fall. That way the work happens the moment the window opens.

What humane exclusion looks like

Every home is different, but a proper, legal exclusion follows the same conservation-minded path. For the complete walkthrough, see our humane bat removal complete guide. In short:

1. Inspection — we find every entry point, confirm the species, and check for signs of an active maternity roost.
2. One-way doors — installed at active openings so bats leave to feed but cannot return.
3. Sealing — once the colony is out, we seal all gaps, from roof lines to soffits, with durable materials.
4. Cleanup and optional bat house — we address guano safely and can set up a bat house to give the colony a new home.

Because no two homes have the same number of entry points, extent of damage, or cleanup needs, cost depends on the specifics of your situation. We look first, then give you a clear, honest quote up front so there are no surprises.

The bottom line for homeowners

White-nose syndrome has pushed several of Ontario’s bats to the edge, and that is exactly why the law now demands they be handled with care. You do not have to choose between protecting your home and protecting these animals. Humane, correctly-timed exclusion keeps bats out of your living space, keeps you on the right side of the law, and keeps the surviving colony alive.

If you have bats in Grey, Bruce, Simcoe, or Huron County, we would be glad to take a look. Request a free, no-obligation inspection through our bat removal and exclusion service page or the home page. Every job we seal is backed by our transferable Lifetime Warranty: if a bat ever gets back in through a point we sealed, we come back and fix it at no charge, for good.