If that ridged area I can see between his shoulder blades sticks up like part of a wheel, he is a wheelbug. I cannot tell how much it sticks up in that photo. Otherwise, he is an assassin bug. Either way, you won't like him (or her or it) because they do feed on some caterpillars with their sucking mouthparts. If it is a wheelbug, it might bite you so be careful around it.

The red and black bug you see that looks familiar might be an immature assassin bug or might be the bee assassin bug. See photos linked below.

Here is a link that might be useful: Assassin Bugs

Ohhh, that is interesting. I don't think I have ever seen one. No caterpillars live long in my yard! If I want any to survive, I have to rear them in the house.

I'm pretty sure the red and black bug is a milkweed assassin bug. I went back out to try and photograph him/her just to be sure, but it was very shy :)

Would the milkweed assassin bugs be eating all those aphids? Something is cleaning them up!

Quite likely, he's a general purpose predator

And he likely is the reason that you have to rear your cats indoors. As far as I know, assassin bugs will eat almost anything, although their method of eating is different from what people might think. They insert their sucking mouthparts (known as a rostrum) into the insect, inject a saliva that liquifies the insect's interior parts, and suck out the insect's innards. (Gross to contemplate, huh?)

I've got cats on the dill and fennel right now and a garden full of assassin bugs. So far, I haven't found the assassin bugs preying upon caterpillars and likely that's because we have so many other insects for them to eat.

Your milkweed assassin bug is very desirable, although a person who gardens for butterflies probably has a love-hate (or a hate-hate) relationship with these bugs since they eat cats. They also eat mosquitoes, flies and aphids as well as just about any other insect you can think of. Their genus is huge with thousands of members, although not all of them are assassin bugs. Some are ambush bugs (they sound just as mean as assassin bugs, but maybe sneakier since they ambush their prey).

I never worry too much about aphids because something will clean them up. In my garden, it generally is lady bugs but there are all kinds of other predatory beneficial insects that also eat aphids. I just saw a new hatch of ladybug larvae on watermelon plants yesterday. I checked the undersides of leaves to see what it is that they are eating---it must be spider mites that are on the menu because I didn't see anything else.

When I see the bad bug population starting to soar, I kinda get that "oh no" feeling, as in "oh no, I hope there's going to be enough predators around to eat all these guys". I don't know why I worry. About a week after I start thinking maybe the bad guys are too abundant, I start seeing tons of beneficials eating them. Remember that your pest bug population has to reach a certain level before the predatory ones start reproducing rapidly. They don't produce their young until there's a sufficient food supply available. It is just like the cottontail rabbit-coyote cycles which are interconnected as prey-predator. At our house this year, you can easily tell the rabbit population is up and the coyote population is down. Next year it is likely to reverse. Garden insects cycle the same way, but probably their cycle up and down mostly is all in one year. Except for grasshoppers---their population cycles up and down more slowly over a period of several years. In our county, the hopper population was high last year and I hoped it was peaking, but it wasn't. There's tons more this year. It isn't the worst grasshopper year we've ever had (yet), but I think it is second worst.