Q.Herb Growing Mystery
I have a thyme plant that shares a window box with a rosemary plant. In the past week, the thyme plant has changed dramatically. The leaves are yellowing and thinning out, and the entire box is absolutely crawling with those reddish-brown centipedes. There’s been no change in water, sunlight, or the introduction of any new food/soil/chemicals since this started happening.
I’ve been doing some reading, and it seems that the centipedes are PROBABLY not eating the thyme roots, but may be eating other root-eaters. But if that’s happening, why aren’t they taking care of the problem? And why is the rosemary perfectly fine? I’m getting food grade diatomaceous earth delivered to me on Wednesday, but I’m afraid the plant will be dead by then. Can anyone help me figure out what’s going on and what I should do? Thanks in advance!!

I would isolate the infected plant and treat with Neem OIl.
https://www.gardeningknowhow.com/plant-problems/pests/pesticides/neem-oil-uses.htm