Worms are NMCs that are small creatures that can be dangerous since they take in numbers and are hard to deal with without Combustion or other area of effect attacks.
These appear early on in Akropolis Tower and then very rarely in the Shelter. They aren't too dangerous and can be killed very easily. Their numbers can be cut down with the shotgun or Combustion.
A much stronger and more dangerous version of the Caterpillar, Maggots have far more HP and consequently are much more dangerous. Combustion works well as it can quickly deal good damage against them in a hurry. They aren't too dangerous however.