My best guess would be most likely a Sphinx moth due to the slash pattern on the sides, but I'm not 100% sure.

Evil things. From their size, I'd say they have already been feasting. Remove as quickly as possible before they strip your plants. Search for more.

Thanks I have dispatched the evil doers and will seek out their kin.

Interesting. I've never had hornworms on my grapes. Thanks for the tip.

You can control any type of caterpillar with products containing Bacillus thuringensis - commonly called "Bt". It's a bacteria that only targets caterpillars and is safe to use around edibles, pets, and fish. A similar product is used to control mosquitoes.

Look for brand names like Thuricide, etc. Mix and spray on your vines. When the caterpillars eat the leaves containing the bacteria they die. It works better when caterpillars are young and you may need to spray several times during the season to catch new generations.

Now keep an eye out for the Western grapeleaf skeletonizer the real bane of growing grapes here. Bright yellow and black caterpillars, with hairs that can give you hives by just brushing against the leaves.
Here's more info: http://www.ipm.ucdavis.edu/PMG/r302301011.html

What is the difference? They (were) are pollinators. And are attractive moths. Bottom line do they eat so much not to be left alone? I would not allow more than one in a single area.

This post was edited by Fascist_Nation on Tue, May 13, 14 at 22:10

I planted Datura last year and the Hornworms left all my plants alone except for the Datura. I think they go for the tastiest plant to them because there were 3-4 on each plant and they cleaned all the leaves off completely. I didn't find any on my tomatoes, grapes, or any other plant.

I didn't really like how the Datura's seed pods looked so I was going to dig them all up, but because of this, I left one alone to regrow this year and see if it happens again.

Yeah, those seed pods are pretty scary looking, huh??

Cut those seed pods off before they get very large to keep the plant blooming. If you are getting seed pods it means your blooms are being visited by the moths that lay the eggs that make those critters. Good advice to me from Grant years ago.

I'd pay you for these if you ever get them again. They are sphinx larvae.

Good suggestion, Andy. I grow tons of datura as well and get, and love those hornworm caterpillars. Happy gardening all!