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THE ASSOCIATION BETWEEN BATS AND HALLOWEEN DATES BACK THOUSANDS OF YEARS.

IT IS BASED ON THE SUPERSTITION THEY ARE OLD AND SOME DEATH.

NOW, NORTH AMERICAN BATS ARE FACING A DEADLY THREAT THEMSELVES.

>> FOR NEARLY TWO DECADES, BATS ACROSS NORTH AMERICA HAVE BEEN DECIMATED BY A DEADLY DISEASE CALLED WHITE NOSE SYNDROME.

PATCHES OF PALE WHITE FUZZ CAUSED BY A FUNGUS APPEAR UNINFECTED BATS.

FIRST OBSERVED IN 2006, THE PATHOGEN QUICKLY BEGAN SPREADING AFTER APPEARING IN NEW YORK STATE.

IT HAS KILLED MILLIONS OF BATS ACROSS THE COUNTRY.

ACCORDING TO RECENT REPORTING, FOR THE FIRST TIME IN YEARS, RESEARCHERS ARE FEELING HOPEFUL IN THE FIGHT AGAINST THE DISEASE.

CARL ZIMMER IS A COLUMNIST FOR THE NEW YORK TIMES AND RECENTLY WROTE ABOUT THIS.

HOW DID THE SYNDROME BEGIN?

WHY DID IT SPREAD SO QUICKLY?

>> IT ORIGINATED IN EUROPE.

IN EUROPE, THE BATS ARE ABLE TO FIGHT IT OFF.

SOMEHOW, THIS FUNGUS WAS ABLE TO GET ACROSS THE ATLANTIC.

IT IS POSSIBLE A TRAVELER WAS EXPLORING A CAVE IN EUROPE AND GOT IT ON HIS BOOTS AND TRAVELED TO NEW YORK AND THE SPORE WAS SPREAD HERE.

WHEN IT GOT TO THE UNITED STATES, THE BATS STARTED TO SPREAD IT ACROSS THE CONTINENT.

>> YOU WRITE ABOUT THE SHOCK SOME RESEARCHERS HAD WHEN THEY CAME UP ON THE FIRST EXAMPLES.

CAN YOU TELL US WHAT IT WAS LIKE FOR THE RESEARCHERS WHO ENTERED THE CAVES AND SAW THE TOLL THE DISEASE HAD TAKEN ON THE BAT POPULATION?

>> THE FIRST BIOLOGISTS WHO DISCOVERED IT WERE SHOCKED.

THEY WOULD LITERALLY WALK INTO A CAVE THEY HAD BEEN VISITING FOR WINTERS STUDYING HIBERNATING BATS FOR YEARS AND THERE WOULD BE A PILE OF DEAD BATS ON THE CAVE FLOOR.

THEY WOULD SEE CAVES COMPLETELY EMPTY.

AND THEN, THIS FUNGUS MADE ITS WAY ACROSS NORTH AMERICA AND FURTHER WEST.

BIOLOGISTS KNEW IT WAS COMING.

ONE WINTER, THEY WOULD GO INTO THEIR CAVES AND SEE THESE HUGE PILES OF BAT BODIES.

MILLIONS OF BATS HAVE DIED AS A RESULT OF THIS.

>> IT HAS RUN RAMPANT FOR SO MANY YEARS.

LOG ARE RESEARCHERS NOW HOPEFUL - - WHY ARE RESEARCHERS NOW HOPEFUL?

>> WE ARE AT A DIRE POINT.

SOME SPECIES ARE DOWN OVER 90%.

OVER HALF OF THE SPECIES IN NORTH AMERICA ARE AT RISK OF EXTINCTION.

WHITE NOSE SYNDROME IS PART OF THAT THREAT.

BUT IT DOES SEEM LIKE THERE MIGHT BE SEVERAL DIFFERENT WAYS THAT WILDLIFE BIOLOGISTS COULD HELP TO RESTORE THE BATS.

THOSE PROJECTS ARE GOING ON RIGHT NOW.

>> WHAT SORT OF SOLUTIONS HAVE RESEARCHERS FOUND HAVE BEEN HELPFUL?

>> ONE POSSIBILITY IS TO USE A NON-TOXIC CHEMICAL SPRAY DID ON THE WALZ -- STRAIGHT ON THE WALLS OF ABANDONED MINES WERE THEY LIKE TO ROOST FOR THE WINTER.

THIS CHEMICAL SPRAY ARRESTS THE FUNGUS.

THE SPORES ARE INERT.

PRELIMINARY STUDIES HAVE SHOWN THIS ENDS UP ALLOWING MORE TO SURVIVE THE WINTER AND NOT GET SICK WITH WHITE NOSE SYNDROME.

THAT IS ONE SOLUTION.

ANOTHER IS TO BRING IN MORE COLD AIR INTO THESE SHELTERS WHERE THEY HIBERNATE BECAUSE AT COLDER TEMPERATURES, IT SEEMS THE BATS ARE ABLE TO GO INTO A DEEPER STATE OF HIBERNATION AND CAN WITHSTAND THE FUNGUS ATTACK.

IN THE SPRING WHEN THEY COME OUT OF HIBERNATION, THEY CAN REBOUND.

>> LET'S TAKE A STEP BACK AND TALK ABOUT THE IMPORTANCE OF BATS TO THE ECOSYSTEM AND WHY IT MATTERS SO MUCH THAT THIS MASSIVE DIE OFF BE STOPPED.

>> A LOT OF PEOPLE ARE SCARED OF BATS.

THEY WOULD RATHER NOT DEAL WITH THEM NEAR THEM.

BUT YOU HAVE TO REMEMBER THAT BATS ARE ESSENTIAL TO MANY ECOSYSTEMS.

SOME SPECIES WILL POLLINATE FLOWERS, SO THE FLOWERS TOTALLY DEPEND ON THE BATS TO SPREAD THEM AROUND.

THAT'S ALSO EAST VAST AMOUNTS -- BATS ALSO EAT VAST AMOUNTS OF INSECTS.

IF YOU TAKE THE BATS AWAY, THE INSECTS CAN EXPLODE.

WE HAVE SEEN IN COUNTIES WHERE THERE'S A HIGH LEVELS OF WHITE NOSE SYNDROME, SO BATS ARE DISAPPEARING, THE INSECTS ARE BOOMING SO MUCH THAT FARMERS ARE HAVING TO PUT MORE INSECTICIDE ON THE FARM FIELDS.

THAT CAN LEAD TO HUMAN HEALTH PROBLEMS.

YOU CAN SEE HOW IF YOU LET BATS DISAPPEAR, THERE WILL BE A BUNCH OF PROBLEMS NOT ONLY FOR NATURE BUT FOR US AS WELL.

>> YOU MENTIONED EARLIER HOW THIS DISEASE LIKELY STARTED IN EUROPE AND TRAVELED TO NORTH AMERICA.

WHAT DOES THAT SAY ABOUT THE DANGERS OF TRAVEL IN TERMS OF SPREADING THESE PATHOGENS FAR AND WIDE?

>> WE HAVE TO RECOGNIZE WE ALL LIVE ON THE SAME PLANET.

AS FAR AWAY AS EUROPE MIGHT SEEM, OR CHINA, OR ANY OTHER PLACE ON EARTH, DISEASES CAN GET AROUND.

IT CAN TAKE JUST ONE FUNGAL SPORE ON ONE BOOT TO ENDANGER ALL OF THE SPECIES OF BATS ON A NEW CONTINENT.

WE HAVE SEEN THAT WITH HUMAN DISEASES AS WELL, WITH COVID FOR EXAMPLE.

COVID STARTED IN ONE PLACE IN CHINA AND IT WAS SOON ALL AROUND THE WORLD.

IF WE ARE GOING TO TRY TO LESSEN THE THREAT OF ALL OF THESE PATHOGENS, WE HAVE TO BE THINKING GLOBALLY.

>> CARL ZIMMER WITH A HOPEFUL STORY ABOUT AN IMPORTANT SPECIES, THANK YOU SO MUCH.

>> THANK YOU.