It's either a tomato or tobacco hornworm. They are voracious eaters. I can almost guarantee you the one your dog ate is not the only one. They so closely match the color of tomato leaves (and datura leaves) that they can be hard to see. You can either pick them off, or spray your plants with BT (the least toxic way to kill caterpillars). When I said voracious...if you miss a big one like that--it could strip the entire Datura overnight.

I am unsure about the toxicity of BT to dogs (it's a bacteria that kills caterpillars when it's ingested so it takes about 24 hours to work and will need to be reapplied periodically). If I were you, I'd pin up your pet until the spray is dry.

I have never seen a blue jay die from eating tomato hornworms, so I think it unlikely that it will harm your pet. Might give him a belly ache if he ate too many, but then dogs eat plenty of strange stuff without a second thought. Call your vet if you're still worried.

Hornworms are not poisonous, nor is Bt. Also, the least toxic method of getting rid of the hornworms is by removing them by hand. ;-) Bt is not particularly effective when the caterpillars are large, but should be applied while still teensy.

Of course THAT requires careful searching!!

All I can say to your dog is: "You're hired".

But the conventional school of thought (especially if you're trying to grow organic) is if the hornworm has what looks like little grains of rice sticking up all over its back, just leave it be. Those are parasitic wasp eggs that will soon hatch and devour their host, and then go seek out more.