Mystery puncture -- caused by inner end of ice spike? I had to change my back tube yesterday and couldn't find anything by eye or by feel on the inside of the tyre, by eye on the outside (it's a schwalbe winter so you can't find anything except its own spikes by running it through your hands). The rim and rim tape were also clean.

Several of the spike bases showed signs of wear on the inside of the tyre, in one case there were threads showing.  By the time I found that I'd taken the tube out, so I just covered it and put a new tube in.

I haven't yet patched the tube (I do them in batches to save the glue drying up on the shelf) but there was no visible damage (or hissing with everything still on the bike).  The tyre had held pressure for a week before feeling low on Saturday and being confirmed on Sunday, so I'm not inclined to blame grit in the valve.

The tyres only have ~1000km on them, last winter and some of this winter.  They've lost a few studs but the tread looks as new.  They've only been used on tarmac (a few spots on my route are prone to black ice).  They've also only been run close to the max pressure, as recommended for hard surfaces.

I'd be happy to dismiss it as bad luck, but if this is an issue I'll fit tyre liners next time I mount these tyres

So: Can the inner end of ice spikes wear through the casing to cause punctures?
The conclusion from the comments was that this is possible -- possibly the threads abrading the tube.  To be on the safe side I'll cover that point with a patch or liner next winter.