I'll comment just because. First off the "Nix" treatment is only for snake mites, therefore it only applies to snakes as the mites are host specific.
Secondly if you were foolish enough to use it around your crickets & spiders it would kill every single one of them & it could possibly make your lizards very sick. I don't know how they would react to it. They would probably get sick if they fed on "poisoned" crickets though & your spiders would die for sure.
Lastly don't treat them with anything until you are sure of what you are dealing with. I'd hate to see your animals suffer due to guessing what "bugs" they are & the treatment to remove them.
I'm more apt to suspect that they may be coming from the spiders enclosures as there is a type of mites that they can carry as well. I would make a post on the spider forum & see what the people there think. Remember NIX is death to all your crickets, spiders, cockroaches etc. & anything that might possibly be feeding on them, seriously Mark I.
Mark's GONE SNAKEE! working with select Colubrids (Corns, GB Kings, EIs) and Woma Pythons
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