In my opinion earthworms are not a good choice for chameleons.
Parasite issues aside, I think this feeder would be hard for them to eat.
Worms are slimy and I don't think they would stick to the tongue well.
Both of my veileds eat earthworms on occasion. A word of caution though, I would only purchase them at a pet store or bait shop that gets them from a farm raised source. These are more likely to be parasite free. Wild caught can be full of parasites. They don't really have any problem getting them to their mouth. It's getting them down that they can have a problem with. One of mine uses his other hand to get the remaining part of the worm into his mouth. They had no hesitation at eating them, went right for them. Good luck. David