I presume this might had been a topic addressed before, but after a recent incident I do feel it needs to be touched upon again.
I am not certain how do Magic Eater Spawns work currently, other than "Cast Spell, % chance of Magic Eaters appearing" being my best guess. Yet I always assumed that their spawn rate depended in part on the spell level. So, the more powerful the spell the higher the chance of them appearing, and the higher the chance of a larger, more powerful spawn appearing as well.
Normally you can outrun a single or two magic eaters, especially with the "hint" or message that they are about to show up. In some areas it is less likely, especially if it's an open space, with no corners to turn around in.
My main issue is, however, that spell levels do not seem to influence the difficulty of their spawns.
Just today, after casting a cantrip, the lowest of the low of possible spells we received a Magic Eater spawn of a Medium and Three "Lights". Since this also happened in a relatively open space with nowhere to hide myself (the caster) was killed over a Lightning Jolt.
Perhaps a small revision of how the Magic Eaters spawns work, especially with lower level spells, is needed. Getting such a massive and dangerous spawn, when casting one of the weakest possible spells leads me to believe that a level 2 or 3 who is simply unlucky enough could be killed outright, not counting a mage who for RP reasons might wish to cast a Light spell and suddenly has an army of eaters on top of him.
I am still a bit angry about dying in such a particular way, but I do feel that casting a very weak spell should not act as a way of attracting so much Eater attention, while a far more powerful spell, that should be akin to a "beacon" for these creatures only brings forth a single one.
Abjurer's Nightshade is 12 gold.
I'm fairly sure the formula for magic eaters is actually rather elaborate, and likely does include spell level among a variety of other things. Might be an interesting IC study for someone ;)
I can't really speak to how they work now, but in EFU1 it was a well known phenomenon that Magic Eater activity was seasonal.
There have been some IG studies on magic eaters and certain magic eater events, and I think some of it has been published. DMs have said their activity comes and goes in phases in season still like efu1. More can be learned IG :)
Folks above have said pretty much all that needs to be said about it. There are quite many factors involved.
I just had another case of an absurdly powerful Magic Eater Spawn, and for no clear or obvious reason either.
We just entered a QA (namely, Rothe Herder Quest). We waited a while for the Rothe to show up and when they did I begun to summon level 1 critters. After just three casts (the other wizard accompanying did not cast or summon anything yet) we suddenly got a massive spawn of eight magic eaters (1 Medium, 7 Lesser). These promptly killed many of our summons, and the Rothe, and some of them even lasted throughout the entire quest, and had to be dealt with even after the hounds themselves were defeated.
I played Wizards and Sorcerers who were far more careless than my current Sorcerer and they never had anything larger than the 1 Medium, 3 Lesser Eater Spawn, and even then it was rare. If there is indeed a period of time when Eaters become more active I can understand that, but 8 Magic Eaters, for a level 1 Spell? I do not think I ever saw an 8 Magic Eater Spawn before.
Sometimes you are just unlucky. Some people almost never get them. But as I said, it has many factors and some change over time.
There is rather good way to protect yourself.
Really...just use the means available, be paranoid about it.
This is not going to be touched. Locked.