Found under our tree in garden (London) - has only been happening in past 4 months or so and has never happened before. I clean them off our table under the tree and then they reappear the next day! They look a bit like droppings but are very dry and... pellet-y! We wondered if they were produced by a bird/animal as they only fall in one patch under the tree so would assume not produced by tree. Anyone seen anything like this?