Why do

Pine cones open when its fine and close when it rains. Was told when I was a child that's what they did. But I dont think I was told why. Any body know. Mine are open and its raining.  

Are they inside or outside?

outside on my nice lovely decorated christmas tree  

They are indicators of weather - amateur forecasters often have one dangling over their back door.  I think the biggest changes are the ones in temperature. 

Thanks Vg. I've just been outside and looked and it looks like they are closing. Its amazing when you consider I've had them 27 years.  

You're welcome.  

I read that ages ago about the weather forecast - not sure how far they can tell in advance though. When I can post a link I will. Birds and insects feed on them too, because there are nuts/seeds in them.