Do you mean something eating them?

I know FOR SURE slugs LOVE basil. In 2012, I planted a red basil. Two days after when I went to check it, it was gone down to bare ground.

Aside from the slug problem: Basil need warm weather. In cold they will either get stressed out or just sit there doing nothing. It is THE most cold sensitive vegetable I know off.

Weird. Kind of looks like a caterpillar damage. Maybe try a little BT?

No snails or slugs here. I am thinking grasshopper. The weather is perfect for them right now. The ones not getting munched look great.

No snails or slugs here. I am thinking grasshopper.
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Throw a piece of nylon/French tulle on them. Then no insects can eat them. not even rats and rabbits. Unless some Earwigs are hiding in the ground next to them.

Or unless you have winter moth caterpillars dropping off the trees, that seem to eat anything they land on. I've had damage from earwigs in previous years, and I didn't figure it out until I went out with a flashlight at night.

This area had a huge earwig problem last year. .. However I have only seen a few so far this season and lat year they didn't disturb the basil, but I also had dahlias planted last year too which they munched on profusely.

If you want to know if there are earwigs, just try removing the mulch from around the basil plant. If there we any will be hiding in the moist under it.
But Earwigs don't eat that much, as compared to slugs. Rats and rabbits are also suspect. So nylon tulle (from any fabric/craft store) can deter many and all.

Today I will be xplanting cucumbers. I will cover them with tulle. Tulle is a versatile thing to have handy and its is very inexpensive cover material. Will let air, light, rain in. It is wind proof, light weight.

How do you secure it to the plant?