I'm no expert on fish or caterpillars but with the info you gave it could be almost anything. I did see one that was black with red hairs but that one was called a Jersey Tiger so I don't think that one is correct especially since you wouldn't be likely to say nubs if you saw hairs. It is not likely it was poisonous since there are very few that can defend themselves that way. (Not a very good defense since it only works if you get eaten.) The real defense is making the eater think you are poisonous by mimicry.
Considering there are many thousands of different caterpillars, not all of whom result in moths or butterflies, you have to come up with a lot more info, including your geographical location (there is a database that deals with caterpillars found in the Pacific North West only).
Sorry, Sandy PS if you figure out which one it is, I would like to know, too.

Thanks for the response, Sandy. I live in a semi-rural area northeast of Sacramento. And my caterpillar doesn't sound like the Jersey Tiger you described. Attached is a link showing the closest image I could find, although I seem to remember that mine had yellow or white markings on it, also...really a pretty cool looking caterpillar.

Bob

Here is a link that might be useful:

I just Googled some info on poisonous caterpillars and although I still haven't identified the one I fed to my koi, I learned enough to know that killing your koi by feeding them caterpillars is clearly a possibility. There are lots of poisonous caterpillars and certain distinctive markings do, in fact, deter birds from eating them. The caterpillar of the monarch butterfly is one example. Their diet of milkweed creates a toxin that also happens to taste bad to birds and they avoid them.

I'm still curious to know the identity of my caterpillar but at least I have a possible theory in my fish's untimely demise and won't be pampering my koi with any more organic dinners.

Bob

Wow, that is some fantastic caterpillar! Some of the pictures look more like art than bugs. Some make me wonder if they are the source of dragon images.
Another confusion is that caterpillers don't look the same as they age. I can't begin to remember even a few.
Sorry aabout your fishie. Sandy

From my several little books on caterpillars, it looks like a pipevine swallowtail caterpillar. I would give anything to have one of those on my property! They turn into beautiful butterflies.
Next time you find an interesting cat, don't throw it in your pond!
It says they are very distasteful, but didn't say anything about them being poisonous.

Yes Bob, It certainly is possible to kill a fish by feeding it a caterpillar. From your description it was most likely some type of swallowtail cat....slugs & grubs are ok to feed but cats turn into such beautiful butterflies.

Wow, I, too, would love to find swallowtail cats in my yard - rural area northWEST of Sac! Yes, they eat stuff, but that's why I bought my California dutchman's pipe vine - so they could eat all they want. :D

Hope you have more of them in the future! Sorry to hear about your koi, too.

Brenda

May I get off-topic here for a minute please?
Brenda.......how are you growing your Dutchman's pipevine?
I've had one in a bad place for years, and need to move it. But life keeps messing up my plans.
I've heard you need a really heavy-duty, permanent structure. How's your's doing?
I saw big healthy ones at the nursery today...........$33. Its an expensive place.
I pulled myself away without buying it.......but I know how to get back there!
:)
Are the pipevine swallowtails attracted to any other plants?

Catherine, I wanted to see what that plant is like and I came across this link. They sell it in quart pots for $10.00. Sandy

Here is a link that might be useful: Sunlight gardens

Wow.....what a great site Sandy! I'm even seeing some other native stuff I've been looking for! Thanks!

Catherine, I'm growing the A. californica, which I got last year around this time. I only have it in a pot at the moment - due to gopher issues and the fact that I'm still not sure where I want it - and a lady over on the CA forum said hers does well in a potted situation. It's still very small, and I paid about $6 for it at a small native nursery an hour north of here.

It's in morning sun with dappled sun throughout the rest of the day. It probably won't bloom for me until at least next year, as someone posted, "The first year they sleep, second year they creep, third year they leap." :)

I've read that if they get too out of hand, i.e., tangled and/or huge, then they can be cut to the ground before spring growth starts.

As far as I know, the pipevine swallowtail, specifically, is only attracted to Aristolochia as a larval food, but swallowtail larvae in general are attracted to many different plants.

Brenda

Thanks Brenda.