Q&A with Customer Service:
Customer Service very, very rarely get anything right, do they?
From the Main FAQ, p52:
There is no set limit to how far away a spellcaster can be
when delivering a touch spell, but the basic requirement is
being able to reach into the space the creature occupies. For
example, a human occupies a 5-foot space. Thus, a foe must be
able to reach into that space to deliver a touch attack, even if a
piece of the human’s equipment (such as 50 feet of dangling
rope or a manufactured reach weapon) sticks out of the space.
A creature with natural reach is an exception to this rule—
you can use a touch spell against such a creature by touching
one of its natural reach weapons, even if its body is out of your
reach. Such a tactic might require some preparation, however.
If a creature can reach you with a natural weapon (such as a
bite, claw, or tentacle), you can ready an action to use a touch
spell against that natural weapon when it is used to make a
melee attack against you.
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Now, this is from an answer to a question about touch spells, which is why it talks about touch spells.
But the principle is clear - when a creature with natural reach makes an attack, a readied action on the part of the defender can be used against the natural weapon.
-Hyp.