Skeli spawner problem

[JeremyLSX]

so i have a skeli spawner built on my island, its just 4 spawners atm im buying 4 more. my problem is they seem to spawn all over the place, all over my island. from what i can see they may be spawning with natural mobs as they spawn on my island. is that correct? so in order to have this working properly i have to have my entire island lit up to the max so nothing spawns?

 

[Asheey]

You need to light it up for them to not spawn.