Bowtruckles: 

A bowtruckle is a tree goblin and are around the size of a human hand. They can be quite aggressive to anyone who comes near their home, that's why they get the classification of XX. However, they can be distracted by one thing: food. They commonly eat woodlice, due to the avalibilty. When woodlice is not available, they will normally attempt to find insects for food instead. 

They have a very intresting skeletal structure, as they have bones like birds. They are very light, due to the amount of air in their bone marrow. Their reproduction is rather fascinating, when they die one of the bones becomes active. The cells start dividing and then reproduce. They are quite smart creatures, since when their tree gets a disease they will move and abandon their tree. 

This is because they are quite weak creatures and can die within 48 hours to fungal diseases! Yikes!