After reading some of the complaints on consumeraffairs, i don't think it's maggots they're finding. Based on the description of the worms and the webbing mentioned, it sounds like pantry moths; the larval form matches the worm description, & the webbing they make before becoming moths. I frequently have problems with them because of our pet birds (the eggs of the larva are frequently in bird seed where they're had to detect). Once they're in your house they're very hard to get rid of permanently and will try to get into any dry goods in your pantry.
I don't think they are what's making the animals sick, tho. My dogs have eaten them without an issue (no, not on purpose). The symptoms sound more like mold; that is toxic to dogs, which i found out the hard way 2 days before christmas when my dogs found a paper plate with mold on it in some garbage a racoon had torn open. The mold symptoms match up with what they're describing. The vet also said they'd seen a huge increase in mold poisoning the last few months.