A Bed of Roses?

I had always thought these round bite marks on roses and other plants were due to some hungry and very methodical caterpillar. 

Then one morning, while having my coffee out on the patio, I saw what I thought was a hornet carrying a round piece of leaf. It flew into the drain hole of my pot of basil. A few moments later it flew out again, without the bit of greenery. What was that about? 

Fortunately I have been stocking up on field guides and, according to Insects of the North Woods, I learned about a group of bees known as Leaf-cutter bees, the Megachile ​species. 

I tried watching for another trip from this individual, but I think she found my pot too damp and has moved on. 

Since then, I've seen several of these bees pausing for a rest with a piece of round leaf clutched to their bellies. It must be hard to fly with something flat and the same diameter as your body clutched between your legs.

One of their favourite building material is rose leaves. And why not? So I lurked near our rose bush until I finally got a few shots of the leaf cutting process.

Unlike honey bees or bumble bees, leaf cutters don't collect pollen on their legs. Rather, hairs on their bellies pick up a coating of pollen. Here's one with a belly covered in fresh pollen.
Several species are used commercially to pollenate crops such as alfalfa. Turns out, honey bees don't do a good job of pollinating alfalfa because they don't like being bonked under the head by the springy alfalfa flower stamens!

An Assassin bug resting on a rose leaf. Check out the lovely red serrations on his one remaining hind leg.