Earthworms in my mulch

I was preparing the planter which will take my tomato seedlings and as I was digging around in the mulching box I found tens of earthworms. *shiver*

What is strange is that there isn't any way they got here themselves. They must be laying dormant in some other medium. Fertilizer? Bagged soil? Polished rice husks? Other plants on the veranda?

They are here to help, and I appreciate that. But man do they get my heebies jeebing.