A new pest problem, the need for a few pests, & my vermicultural experiment begun

Here is a photo of some damage from a pest that can be beneficial to your garden, but if left unchecked can wreak some serious carnage upon your greens:

This is my spinach, coming along nicely except for the large, ragged holes and torn pieces. We'll get back to it in a minute, so try to figure out the particular pest.

It is nice to have some pests like aphids around,
and here is why:

The benefits of ladybugs only accrue if they have something to eat. Here this little critter is walking on my brandywine tomato plant, looking to kill something.

Ladybugs have at least two grand purposes in our garden. First, they kill many plant pests. Second, and just as important, their bright coloration makes it easy for our daughter to spot them and get all excited.

However, if we had sprayed the entire garden with pesticide, no matter how "green", we would not have the opportunity to see these great little beetles. They would have checked out the place, found it barren and hostile, and bugged out or worse. Now, because we had some aphids and such, we can always find a few ladybird beetles out and about on our plants. Our plants do not look worse for the wear, either.

It's about balance and trust. If we steward these things, watching for cues from the activities around us rather than trying to muscle in and put everything in its place, then we get surprises we hadn't expected, or had anticipated.

Which brings me to my vermiculture experiment. Last year, I realized I wasn't going to be able to get a hot compost pile going. I just don't get it, and I also think I just don't have the property size to sacrifice for it plus the garbage waiting its turn. So this year, I decided to try a compost bin. I didn't want to go big to begin, so I bought to 18 gallon Sterilite tubs, punched holes in one. shook it every couple of days while I added material to it. I overdid the nitrogen, of course, because it got slimy and buggy. I wasn't getting that one, either.

So now, I'm trying worms. I filled about 4/5th's of the holey tub with straw from the ducklings' bedding, buried it about 1/2 way into the ground behind the garden, and threw in 100 red worms from the local bait shop. I've since added coffee grounds and some green scraps, as well as some composting leaves from a pile from last year.

At first, I'd seen many little flies, but in the past couple of days they have dropped off. But, so has the temperature, so that may not be due to the worms. I do think I need more worms, and will purchase some shortly. I'll also try to keep folks posted here as to the relative success of this composting attempt.

Okay, back to the quiz. Have you figured out the pest that, if left unchecked, can wreak devastation to make a slug green with envy? It is none other than that ravenous Anas platyrhynchos...