Most likely, the pickle worm. They are really bad in the southeast. If you are not squemish, you might try cutting up the squash. They usually make quite a mess inside the fruit tho.

Pickleworms have really ruined my squash and melons this year.
Go ahead and cut the squash.
I was about to throw away a watermelon that had a pickleworm hole in it.
I cut into the watermelon and the hole stopped in the rind.
I was able to still eat the watermelon.
My summer squash are ruined though.