I am losing larva to the woodpeckers, I still get lots I usually have well over a thousand cocoons every year. But if I run out of suet the woodpeckers are on the bee houses right away, there is one Hairy that you have to open the door and chase him away, banging on the window does nothing.
Use good thick wood since they will try to access the larva through the side.
I still haven't cleaned my cocoons yet this year, the houses are sitting where it is dry and cold, I found out that you can clean the cocoons anytime as long as you keep them cold, its nice to do it where it is warm so best to do them before December, after December warmth will wake them up. I also found out that if they get all moldy in the fridge you can give them a wash in the weak bleach solution and they will all be fine.