Bought a frag the other day and noticed this in a hole and wondered what it is and if I should remove it. Hard to get a good photo as it is quite small.
If it is small, peppermints might do the trick but for me you cant beat the smell of burning aiptasia - fry the monsters - get a kitchen blow torch or a soldering iron and burn em I like soldering irons the best as you can stick it in their hole