Slugbulbs live in caves that will usually have Glow-worms and Eletricstickys. Hiccup and crew encounters them in the caves beneath Flashburn's School of Swordfighting in How to Steal a Dragon's Sword.
Slug bulbs appear to be able to glow or fluoresce based on their pictures and name.
- How to Steal a Dragon's Sword (Book 9), Cressida Cowell. 2011
- The Complete Book of Dragons: A Guide To Dragon Species, Cressida Cowell. 2014