What is not mentioned in the text, is whether the medium is consumed by the creation of the vermin. Is there less water in the pond after I create a thousand frogs in it? If I create Scorpions from hot, dry dirt, is there a hole where the scorpion came from? Possible consequences would include the following spell.
Pit of the venomous scorpions
R:V, D:M, T:G
Turn an area of dirt 6 paces wide by 9ft deep into a hole filled with Scorpions. These 9000 scorpions will be completely mundane and bypass parma magica.
Base 5, +2 voice, +2 group, +1 size
It does not mention in the text whether the created worms must be native to the area. Therefore a knowledgeable magus could use a simple ignem spell to dry out a patch of land in france, and then create scorpions from it.
Do worms appear in magically created mediums? If you create a pool of water with a month duration, can you use rego to cause frogs to appear.
Does this worms process use the standard creo rule for creating things you have knowledge of. This means that you can only create worms that you could create using creo magics or does it mean that if someone informs you that water generates frogs, you can cause it to generate the frogs - even if you have never seen a frog before.
A variant on worms is stagnation - everyone knows that water left alone will become undrinkable and smell.
Curse of Stagnation
R:Sight, D:Mom, T:Group
The well, pond or pool you target stagnates to become undrinkable and give off noxious fumes that can cause diseases. This spell was created by Nortilaus of Jerbiton to surepticiously help beseiging troups.
Are mushrooms and weeds considered as worms? Mushrooms appear overnight anywhere it is dark and damp, Weeds appear everywhere no-matter how well you examined your soil.
Grow in the Dark
R:V, D:Mom, T:P
Causes a carpet of mushrooms to generate at the desired location. The mushrooms only appear from damp earth and are each a few inches wide. Ten cubic paces of damp earth generate 1000 mushrooms.