Question
We have a mature pin oak hanging over our deck (North Carolina).  We have lived here 10 years and for the first time the tree appears to be dropping tiny "pellets".  We first noticed that when these "pellets" (which are quite hard and approximately 1/16") have dropped into our bird bath on the deck, within a short period of time they grow, turn green and appear like algae in the water.  We have no idea what these are and why now, after ten years, they are now appearing.  Any ideas?  Thank you ever so much for any input.

Answer
Jan:
I suspect these structures may be insect related- perhaps "poop".  If you want to, you are welcome to send me a closeup photo of several of these "pellets" together in group.  Get as close as you can and lay a ruler beside them for a reference.  Review your photo on the computer to be sure it is in focus before sending.  They are probably dry, soak up water and swell.

I suspect they are more of a nuisance than anything else.  You may have to tolerate these things for a while.  Many insect are periodic, that is they may stick around for a season or two, then go away for awhile.

Steve