haunted hivemind
Powerful magicians, witches, and wizards are often warned in their studies that casting Necrosight - a spell to see nearby spirits - is more dangerous in forests and nature. Colonies of ants, beehives, even large scale bird aeries can hold thousands or, in some cases, millions of spirits of insects and animals who have recently passed. The warning is partially against sensory overload; the moment the spell is completed, there can be an inundation of creatures who, in death, carry on with their tasks. Ghost worker ants fight against poltergeist wasps while ethereal birds swoop in and swallow them whole.
The primary warning, however, is that the caster must not react to the new world that suddenly encompasses their surroundings. To do so is to invite countless coordinated hauntings. Intangible ravens and crows will work in tandem with bees and grasshoppers to nip at the caster's soul in hundreds of agonizing ways. As with the physical world, the spiritual world will invade interlopers and cause havoc in unexpected ways.
Remember: responsibility towards the natural world does not end at death.