Soul Eater Bugs will most likely be found alongside one or more Spituras. The reason for this, is that their ability Prey will kill the Spitura, but make the Soul Eater Bug far stronger. While Prey is not dangerous to you, Prism is; and if the Soul Eater Bug is roided up on Spituras, don't be surprised to see Prism do well over 200 damage on your front row party members, and 100-150 more on your back row. Their weakness is Fire, so a Flare spell should take these guys down easily enough. At most, another physical attack will finish them off.