BOSTON -- You may not consider bats cute and cuddly, but they do help us out. They help pollinate crops and control insect populations.

That's why scientists are so worried about a mysterious illness that's killing thousands of bats in the Northeast.

NewsCenter 5's David Brown reported Tuesday that walking up to the state's largest bat house, Boston University biologist Dr. Tom Kunz is frustrated and yet challenged by what scientists call White Nose Syndrome.

VIDEO: Mysterious Illness Killing Bats

Nestled up in the rafters are 500 pregnant female brown bats. While these bats are healthy, tens of thousands died over the winter as they hibernated in caves and mines.

"There's no smoking gun there, yet. Over 46 different species of fungi have been found and identified on the surface of bats but none of them are pathogenic," Kunz said.

Photographs from local caves show white fungus circling their noses.

"It is very, very frustrating and yet, you know, the challenge to try to determine what are the under lying causes -- there are multiple possible factor," Kunz said.

Many scientists are racing to figure out if an infectious agent, toxin, or a combination of factors is killing bats. Some are pointing fingers at pesticides used to kill off insects in large numbers.

Bats play a key role in our ecosystem. In fact, one bat has the potential to eat thousands of insects every night during the summer. So a dramatic drop in the bat population means a huge change in other populations.

"Bats help control or suppress the populations. It's important to understand the underlying cause of this. If we can mitigate that in some fashion," Kunz said.