The above link has three videos (you may have to swipe to see the other two) of some large hornets or wasps I found on 27 Jun 2018. These wasps seemed interested in the tomato and watermelon plants, but especially the tomatoes, and especially the Stick tomatoes (I observed them several times besides this, and they gravitated toward the Stick tomatoes; I had two plants). Their preference for the Stick tomatoes isn't obvious from the footage (that's just an observation I made; I saw them quite a few times without making videos).
One of them (not in the video) was huge! It must have been about four inches long. I'd never seen anything like it. I only saw it once, but it was faster than these smaller ones in the videos (which are really fast, if you can't tell; they can change directions and fly faster than regular wasps, kind of like hoverflies fly). The big one could dart across my backyard in a second, probably. Due to its prowess, I didn't tarry too long. Fortunately, it didn't attack, even though I made a hasty retreat after I observed it, awestruck, for a while. I believe it also liked the Stick tomato. It wasn't arched much like a regular wasp; it was fairly straight, and somewhat longer proportionate to its width than the smaller ones.
The wasps would fly from plant to plant for the duration of their visits. They didn't do anything else in particular. They didn't fly around looking for places to build nests like our regular wasps.
The aforementioned 'smaller' ones are still about an inch and a half long or so (even though one appears to be the size of a regular large wasp in part of the watermelon video; it was bigger than it looked; well, they all looked bigger in person, but especially that one, although it was probably the smallest of the three).
They had bolder stripes than our other wasps, and looked thicker in general.
They're possibly Vespa mandarinia (apparently those are in Idaho now, although they weren't reported as early as my videos here), or maybe a hybrid. I'm not sure. I think their heads may have looked different.
I wonder if I'll see them again if I plant more Stick tomatoes.
In the video where you see one on a Stick tomato, listen for the sounds of its wings as it flies.
I haven't seen these since maybe July of 2018, I think. Maybe I saw one in 2019, early on, but I don't think so. I never saw them before 2018. (But we've long had plenty of small and large wasps of other sorts—not this large, though.)
I haven't noticed a decline in bees, particularly. So, hopefully these aren't killing them.
I don't know why the wasps were monitoring my plants regularly, nor what they liked about the Stick tomato. I found them very fascinating creatures. They never bothered me at all, either.