how to prevent worms from escaping

I am working with a nematode species that tends to escape the plate. How can I prevent worms from escaping? I am not so concerned that they are going from one plate another (because I could simply use parafilm), but for the fact that most of them die in the wall of the plate. I want to prevent these worms from crawling in the walls.

I heard that I could use 4M fructose or 2M glycerol as repellents. However, they diffuse within 45 minutes. Other suggestion is 1M copper chloride. However, I think this is toxic to the worms and I am afraid that it could affect my experiments. I would need something that is not very toxic to the worms and that would prevent them from going to the wall of the plate.

Any ideas?

This question is also in the general section from last year but if they arn’t what you want, what i might try is teflon tape. This is effectivly used around fruit trees to stop ground invasion by various insect pests in agriculture.

we use solid copper rings that are flame heated then melted onto the agar surface to contain worms for longer periods. It works for a while, but worms can still burrow under agar after a day or so. Perhaps this problem would be solved with denser agar. See this paper.

Davies AG, Pierce-Shimomura JT, Kim H, VanHoven MK, Thiele TR, Bonci A, Bargmann CI, McIntire SL. A central role of the BK potassium channel in behavioral responses to ethanol in C. elegans.
Cell. 2003 Dec 12;115(6):655-66.

I have had good luck with using palmitic acid to keep worms on plates. Dissolve palmitic acid in ethanol (10 mg/mL), then put a ring of the palmitic acid solution around the edge of the plate. The ethanol will evaporate, and the palmitic acid will precipitate out and form a crunchy barrier that worms don’t like to crawl through. It isn’t 100% effective, but does pretty well keeping most worms on the plate.

I am also running an experiment in which the worms try to crawl off the plates at high frequencies. I am a bit confused about the copper ring method though. Do the worms have an adversion to the copper itself, or is it just the presence of a physical barrier that keeps them contained?