
Preferably, before putting them back, you could use a damp qtip or something similar to wipe each of them off as much as possible, to make sure there is no residue left. If you wanted to be safe I'd take them all out, empty and rinse the container, fill it with a better material (I've heard of keeping mealworms on oatmeal, something like that could work) and putting them back in there for a while before feeding. I'd guess though, that if they were on pine or cedar the worms would be having problems. The superworms I got from our local petsmart were definitely not on pine or cedar, but I can't really speak for those found elsewhere.

If in doubt I'd probably avoid it though.

Usually pine and cedar have a distinct aroma to them, so you should be able to tell for sure by the smell from the container.

The oils are used in some insecticides, so I'd guess there are LOTS of things out there that are at risk from toxicity from them. I would think the mealworms would be just as susceptible to the problems of these woods as Tarantulas (or reptiles, rodents, cats (oils from pine are toxic to cats, the fun things to learn as a vet tech), etc). I would venture a guess that they probably wouldn't be kept on pine or cedar, since both of those have some toxicity to just about everything, due to the oils, etc.
