It isn't possible to keep insects out of a player piano if they want
in, but it is possible to discourage them just a little.
In the first place, insects don't like an instrument that feels as
though it is a different temperature than the rest of the house, as
this is an indication to it that the box is not safe. So despite what
everybody says about those heating bars made by Dampp-Chaser, they
work to keep certain bugs away.
Hard-shelled insects, like carpenter ants and termites, are the most
dangerous of all the insects. They really pose a threat in some areas.
If the piano is going to reside in that sort of climate, I would
suggest that the parts be sprayed with a saturated water solution of
boric acid and left to dry quickly with a fan. The boric acid
solution could be soaked into a felt cover and used to protect the
stack as well as can be expected.
Some layouts wouldn't allow it. On grands, spread boric acid powder
on the bottom cover and anyplace that you think bugs would hide. This
is a permanent solution and doesn't have to be repeated from time to
time. After a while, the electric motor fumes, the oil, and rubber
particles inside the grand create a stench to the bugs that they don't
like, and they leave anyway.
As far as spiders and moth worms, the bad ones are the ones that
make those little webs inside the nipples and the stack. Take moth
crystals, pour them onto some sticky tape, and stick the tape up
somewhere inside the player. New felt is all mothproofed, anyway.
But old felt that has been partially eaten and retained in an action
will actually draw more bugs.