Mana Weevils are bumble-bee sized insects that are attracted to the flow of arcane magic in a living host.
Swarming like mosquitos, they land on the person with mana in their system (either from just casting or currently casting) and will 'sting' them with their long nose.
In actuality, the sting is the weevil implanting their larval young just under the skin of the host. The more mana within the host's body the faster the larva will mature and eventually dig its way out of the host's skin.
Mana weevils live in warm moist areas like the Great Green Sea. Cold weather will kill them and their young.
Mana weevils are also attracted to items enchanted with arcane energy although not as strongly as a live caster.