Epidemic Disease of Bats: White-nose Syndrome

Map showing extent of WNS occurrences in North America - link to larger map opens in new window
Map showing extent of WNS occurrences in North America (click to enlarge)

White-nose syndrome (WNS) is a disease caused by the fungus Pseudogymnoascus destructans (Pd). The disease is estimated to have killed more than six million bats in the eastern United States since 2006 and can kill up to 100% of bats in a colony during hibernation. Until recently, the disease had been spreading slowly in eastern North America from its point of origin in upstate New York. However, in March 2016 a case of WNS was confirmed in a little brown bat (Myotis lucifugus) in Washington near North Bend (30 miles east of Seattle). This is a jump of about 1,300 miles from the previous western-most known occurrence of the disease in Nebraska and Minnesota. WNS has continued to spread in Washington State since 2016.

In July 2019, CDFW and U.S. Fish and Wildlife Service (USFWS) announced surveillance results suggesting the fungus that causes WNS is now present in California. As part of a national surveillance program for WNS and Pd, swab samples have been taken from Myotis bats at sites around the northern part of California. In 2018, a single sample from a bat in the town of Chester had a low-level detection of the fungal DNA, and in 2019, three bats sampled in Chester had positive, though low-level, results for the fungal DNA. In 2023, for the first time, two Myotis bats from Humboldt County tested unambiguously positive for the Pd fungus, and 11 bats from throughout the state returned low-level positive results. See CDFW's 2023 WNS Surveillance Summary Report for more details. At this time, there is no indication the disease itself has taken hold in California bat populations. However, surveillance results like these elsewhere in the country have preceded WNS occurrence by one to a few years.

The fungus grows on and in the skin of bats during winter hibernation, in some cases giving them a white, fuzzy appearance on the muzzle, wings and ears. The fungus invades deep skin tissues and causes extensive damage. Affected bats arouse more often during hibernation causing them to burn up fat reserves needed to sustain them through winter, leading to starvation and death. Wing damage may also cause problems with physiological processes such as blood circulation, thermoregulation, water balance, and gas exchange. Impairment of any or all these processes may also lead to death.

Report a Sick or Dead Bat


Species Affected

To date, seven hibernating species of bats in North America are known to be affected by the disease. These include:

  • Big brown bat (Eptesicus fuscus)
  • Cave bat (Myotis velifer)
  • Eastern small-footed bat (Myotis leibii)
  • Gray bat (Myotis grisescens) *endangered
  • Indiana bat (Myotis sodalis) *endangered
  • Little brown bat (Myotis lucifugus)
  • Long-legged bat (Myotis volans)
  • Northern long-eared bat (Myotis septentrionalis) *threatened
  • Western long-eared bat (Myotis evotis)
  • Southeastern bat (Myotis austroriparius)
  • Tricolored bat (Perimyotis subflavus)
  • Yuma bat (Myotis yumanensis)

Little brown bats, Yuma bats, long-legged bats, western long-eared bats, and big brown bats occur in California, in addition to several other species that are potentially at risk in this state.
Other bat species that have been shown elsewhere to carry the fungus (but apparently do not suffer from the disease WNS) and that occur in California include:  Mexican free-tailed bat (Tadarida brasiliensis), silver-haired bat (Lasionycteris noctivagans), Townsend’s big-eared bat (Corynorhinus townsendii), and western small-footed bat (Myotis ciliolabrum).
There is currently no indication that humans or other animal species are susceptible to infection with the fungus that causes WNS.

Visible signs of WNS

Signs of WNS in bats include:

  • White or gray powdery fungus seen around the muzzle, ears, wings, limbs, or tail of bats;
  • Bats exhibiting yellow-orange fluorescence on hairless skin under long-wave UV light;
  • Excessive or unexplained mortality or population decline at a winter hibernaculum;
  • Delayed arousal from torpor following disturbance;
  • Aberrant behaviors (found on ground inside or outside a hibernaculum, roosting near hibernaculum entrance, increased bat activity outside a hibernaculum or premature return to summer roost during freezing weather);
  • Thin body condition or dehydrated appearance (wrinkled and flaky appearance of furless areas);
  • Moderate to severe wing damage, including membrane thinning, depigmentation, stickiness, holes, tears, or flaky appearance on bats found outside of a hibernaculum or at a summer roost.
Normal wing of little brown bat. Photo: Greg Falxa, WDFW
Normal wing of little brown bat.
Photo: Greg Falxa, WDFW
Wing membrane damaged by Pd fungus.  USFWS/Ryan Von Linden, NY Dept Environmental Conservation/SPL
Wing membrane damaged by Pd fungus.
USFWS/Ryan Von Linden,
NY Dept Environmental Conservation/SPL


WNS appears to spread primarily through physical bat-to-bat contact or infected environment-to-bat contact. Humans have the potential to spread the fungus to new locations as it may attach to clothing and gear used in caves, mines and roosts. Fungal spores are very resilient and may survive in the environment for long periods of time. People who visit bat roosts, caves, and mines are strongly urged to decontaminate all clothing and gear immediately afterwards by using appropriate cleaning and disinfection protocols (see link opens in new tab or window U.S. Fish and Wildlife Service Decontamination Protocol


  • Contact the California Department of Fish and Wildlife or the U.S. Fish and Wildlife Service immediately if you see bats with signs consistent with WNS, or if you see bats flying outside during freezing temperatures.
  • Do not handle live bats. Please refer to the online reporting form for information if you have found a sick or dead bat.
  • Avoid entering caves, mines or other areas used by bats for unnecessary reasons to avoid disturbing bats and potentially spreading the disease to unaffected areas.
  • People who must enter caves, mines or bat roosts should decontaminate all equipment and clothing immediately after visiting. Do not allow dogs and other pets in caves (they may act as carriers of the fungus to new sites).


Bats are valuable members of ecosystems around the world, saving farmers in the U.S. alone over $3 billion annually in pest control services. One colony of bats can consume many tons of insects that would otherwise consume valuable crops and forests, or otherwise threaten human health and well-being. Many species of bats also have a valuable role pollinating plants and dispersing plant seeds.

Over six million bats are estimated to have died due to this disease over the past few years in the eastern US and Canada, with as much as 100% mortality in some colonies. This disease could possibly lead to the extinction of some bat species.

How is CDFW Addressing the Threat of WNS?

The California Department of Fish and Wildlife is working with the U.S. Fish and Wildlife Service and other partners to respond to WNS in California. Our actions include:

  • Continued surveillance for the disease and the fungus that causes it throughout the state and more intensive surveillance in and around the recent site of Pd detection.
  • Baseline monitoring of bat populations, both statewide and at sites in the vicinity of the recent Pd detection.
  • Research to better understand where bats in the area spend their winters.
  • Education and outreach efforts to inform the public and other agencies about WNS.
  • Coordinating with other state wildlife agencies and the U.S. Fish and Wildlife Service on response planning.
bat with white substance on muzzle and ears
Bat with visible growth of Pseudogymnoascus destructans (Pd) fungus on muzzle and ears. USFWS Photo.

WNS Key Findings

  • White-nose syndrome causes very high mortality (up to 100%) in bat colonies during hibernation.
  • The pathogen responsible for the disease is Pseudogymnoascus destructans (formerly Geomyces destructans).
  • Bat-to-bat and infected environment-to-bat contact appear to be the primary transmission routes, although the fungus can also be carried on clothing and equipment to new locations and thereby spread the disease.
  • The fungus and disease have been spreading across North America towards the West and into Canada.  A new occurrence of WNS in the state of Washington was discovered in March 2016.
  • Many species of bats in California are potentially susceptible; currently seven species are known to be affected.