Scientist theories as to why include a mite that attacks bees, pesticides that kill the insects, habitat loss and even bad nutrition for bees.

And the cause for concern goes well beyond the collapse of honeybee colonies.

Bees help pollinate 35% of the world's food.

The Franklins Bumble Bee alone would help pollinate cranberries, blueberries and melons.

But that type of bee may already be extinct.

Vacuum in one hand and net.

And the other robbin Thorp, is on a quest.

We're coming into the area where I last saw Franklin.

He's searching the mountains of Oregon for Franklin's Bumble Bee.

It's a species he's believed to be the last person on earth to have seen alive, and he's got a sample of the B in the back of his truck.

It's from the 19 fifties on.

This is Franklin's on.

You can see she has a black face, a touch of whitey share.

Pretty subtle misses a bee that could be extinct in the wild.

Could be I'm not willing to give up on it, but, uh, I'm hoping that's still out there under the radar.

Last time you saw it was 2006 exactly 10 years before he invited me to join him.

Thorpe is 83 now, a retired professor from UC Davis, and mostly he works alone, day after day, year after year, I spent two days looking for Franklin's Bumble Bee with Thorpe.

I found the work absolutely maddening.

The ones that you hear fly by your ear.

I'm always a spare.

Well, that must have been a Franklin.

I don't think you can put an economic value on the species.

They're all priceless, really.

But Franklin's is one that I've had a lot of personal investment in, And uh, yeah, I feel an attachment kinship to it.

I'm not sure whether he'll find it, but maybe that's beside the point.

The truth is that for anyone to know a species like Franklin's Bumble bee had vanished.