Little stick "houses" all over my garden

I am hoping that some wonderful gardener out there will know the answer to something I CAN'T find (so far) on the internet.  I hand-cut all my dead twigs, etc. for mulch.  I spread it neatly around the plants and then a couple of days later I go out into the garden to find that there are little piles of twigs all throughout the garden.  I would appreciate any information on what is going on!  Thank you.