This object, found on the door of my plastic garden shed, appeared at first to my naked eye as some kind of insect eating the larva of another. I thought it might alternately be a cocoon caught in mid-development. So I photographed it, applying additional magnification. The object measured 14 mm end-to-end. My photograph revealed my speculations were wrong. I think this is an egg case (ootheca) of some unknown insect larva. And the larva is just emerging.

Very gentle probing showed it to be stuck to the surface of my shed door on the upper end. The larva does not dislodge. The egg case appears to be encrusted with fine gravel.

None of my field guides have anything to assist identification via oothecae. Nor was I able to find anything on the web. Identification will require far more studious minds than mine.