Slugbulbs live in caves that usually have Glow-worms and Eletricstickys living in them as well. Hiccup and crew encounter them in the caves beneath Flashburn's School of Swordfighting in How to Steal a Dragon's Sword.
Slugbulbs 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