I've a dim recollection from this forum 2007/8, someone posted a picture of a rolled fern leaf; this was from a moth cat that was carnivorous during certain instars. I don't recall an aphid connection.

I would think cat/aphid close proximities would be pretty common in nature.

And it is not a syrphid fly larva? They are small and green and can have a stripe. They eat lots of aphids. Good for the garden and the flies are cute. If a fly can be cute...
-Elisabeth

The reason I asked this question in the first place was because of that caterpillar that I had last year. I never could figure out what it ate, and so I was worried that I would have problems with these ones, too. However, the question has been answered. I brought in one more caterpillar of the same kind (same size as the larger of the two previous ones), and put the three caterpillars in two containers with alfalfa leaves. All three have eaten the leaves, and it looks like the larger two are spinning hollow, silken structures, as if they might be preparing to pupate. I think the smaller one may have molted into its last instar yesterday.
Speaking of syrphid fly larvae, though, I have removed two of them from the alfalfa that I washed and then put in for the caterpillars. For being legless, those larvae sure can hang on to things! I have them in two (separate) containers that I have been stocking with aphids. So, yes, I'm raising maggots!
And you thought people looked at you strangely when you told them you raise caterpillars....
-Jmcat

At this point, all three caterpillars have pupated, and so have the two hoverfly larvae. However, I am raising another maggot that I found as a hitchhiker on an aphid-covered stem.
-Jmcat

Congratulations! I think the hoverflies should be fun. Awfully cute. I can remember seeing them as kids and thinking they were neat. The only flies I like!
-Elisabeth

Well, the "caterpillar" mystery has been solved. I looked in their cage yesterday, and saw two weevils in it. After some research today, I confirmed an ID of alfalfa weevils (Hypera postica). So much for the strange new lepidopterans that I thought I was raising. Oh, well.
-Jmcat

Ha ha..But think of how much you've learned. Sometimes the only way to ID a thing is to raise it out. In the process you learn So much! Thanks...Maryann

Yes, I did learn the answer to a question that had been bugging me (no pun intended) for a year. I think that one of the hoverfly pupa may have died, but the other one eclosed yesterday. It was so cute! It had a skinny abdomen with metallic green stripes. Unfortunately, I couldn't get a good picture of it before it flew away. I brought in two ladybug larvae yesterday, and another hoverfly larva of a different kind today to raise. Speaking of which, the ladybug larvae were both on the same piece of parsley, so I have them in the same container. They are equal in size. If I keep them with plenty of aphids, do I need to worry about cannibalism, or should I separate them?
Thanks,
-Jmcat

The linked page has some cool GIFs of carnivorous caterpillars at work.

Here is a link that might be useful: A guide to the ravenous hellbeast that is the carnivorous caterpillar