What insect or small mammal is stripping the stem cover or bark from my small Cosmos? Similar appearance to a starving mouse stripping bark from a small tree trunk, but the young Cosmos stems are only 1/8 or 3/16" in diameter.
Snails, slugs, 'roly poly' and any of several other soil type 'creepy crawlies'.
Make a ring out of stiff cardboard (1/2 gallon milk carton is a great size, just cut it into several rings about 3" high.). Sink it into the soil maybe 1/2" deep around the Cosmos, and let it stick up a few inches.
Check at night with a flashlight.
Roll a few sheets of newspaper into a roll that is somewhere between snug and a bit loose. Set these perhaps a foot or two away from the plants. Leave them overnight. If you want to see what you have trapped, open the roll in the daylight into a bucket. Keep replacing the rolls. Never leave them out two nights in a row. You are trapping, then removing the pests.
I will do as you suggest tomorrow. We do have a lot of slugs and snails in wetter places, but that was so dry on top of the ground, I did not think it could be those. They do have some big Statis close by that would give them plenty of cool shade to hide under.
Snails were the culprit, as i put out some snail bait and found a lot of dead ones this morning. But without seeing it, i would have had a hard time believing that a full grown snail could climb a 3/'16ths stem and eat the bark all the way around.
The snails have lived under some Statice plants, which they do not harm, and i have not seen any slime tracks, so did not know they were there.