Locked room mystery...

My compost pile has produced a locked room mystery of sorts. Seldom turned, the unmanageable heap of organic waste typically yields at least one mystery crop, usually acorn squash, pumpkins, or melons. This year, the mystery produce kept dying before I could identify the crop. I hoped for watermelon. Turns out it's immature acorn squash that's infested with green caterpillars or worms, yet there's no visible sign of the bugs' entry and the vines continue to thrive. It's as if the bugs have grown within the core, maturing as the plant developed.