If you saw any pretty moths flying around, that may be the culprit. It lays eggs in the stalk like it would an iris then the caterpillar eats down the inside of the stalk and destroys the base of the plant. A couple of stalks might survive for a while but will eventually die.

I never saw any moths, but that certainly doesn't mean they weren't there. The caterpillars I found were about 2 inches long, black with 2 yellow stripes down the sides. I killed the ones I found. The plant isn't showing any signs of growing so I'm wondering if I should just throw it out and get something else. Do the moths you're talking about specifically attack the celery plants?

No, moths can be pretty picky or they can eat most anything. The iris borer is, I think, pretty specific and is pink.

In general there just isn't enough info. I don't know where you live, is the caterpillar hairy, does it have a split tail, is it smooth, what shape is it? All sorts of questions and I don't have a reference for the multitude of possibilities.The only way to determine if it is a borer type is to cut open the tuber or base and go from there.

Sorry I can't help much.

Water celery is the larval food for the Swallowtail butterfly. Your description of the caterpillar sounds like a swallowtail. They eat the foliage but do not bore into the plant. I don't know why it would have died.

Frankielynn, thank you! I looked at that photo several times and thought it just didn't look like the one Aggierose described.

Oh man, I hope they weren't butterfly larvae! I'd never kill them if I knew they were butterflies. I thought they looked like army worms when I looked them up.

I just looked it up and they definitely were not swallowtail caterpillars. The ones I am finding are solid black with 2 yellow stripes running legnth wise on their body. One stripe on each side. They are not hairy and are 2-3 inches long. They are close to the thickness of a pencil, maybe a little thinner. The only plant I've found them on is my water celery, but they ate my hostas too, at least I think it was them! I still think they look like army worms.

Well, I found a photo of one that seems to look like what you describe, but there is no accompanying info. I wish I knew of a good reference but I haven't ever come across one. I think Army worm or Army caterpillar must be generic and describes behavior. I saw a lot of caterpillars that were called Army caterpillars but they were all very different. We had an invasion here several years ago and they were actually the color of old fashioned army fatigues green. There were thousands, all marching the same direction.

Here is a link that might be useful: {{gwi:224026}}

Yes, that is the worm I have! Are you sure that it's a butterfly caterpillar??? If I've been killing butterflies I'm going to be so upset!! I looked up caterpillars for hours before I started to kill them trying to make sure they weren't butterflies!!

I think most "army worms" or Caterpillars are moth larva.

I know that many moths are not as pretty as butterflies but some are spectacular such as the Luna moth and the Hummingbird moth. They also fill the same environmental niche. Their larva cause the same type of woes for gardeners.

It is an ugly brownish moth and the info said that army worms will start in one place and eat anything and everything. It needed killing.

Agreed.