Psyllids or 'jumping plant lice' (Hemiptera - Psylloidea) often look like small cicada. The adults can often jump and fly. The real galls are caused sap sucking larvae who inject a liquid.

Livia junci (juncorum) ocauses attractive, often pink coloured rosettes on many species of Juncus. 

 Psyllopsis fraxini or P. discrepans are psyllids causing galls on the leaves ofFraxinus excelsior. The galls cannot be distinguished. The gallers can be distinguished on base of the nymphs. The edge of the leaf curles down and the cells become enlarged strongly. The gall coloures pale green, wite, pink and is often with red or purple veins.  

Trichochermes walkeri causes a thickened and rolled leaf margin of buckthorn,Rhamnus cathartica. The roll is about 0,5 by 2 cm and pale green and contains blue waxy aphids. It is not a very common species in the Netherlands. In Amen, Drenthe, I saw some galls on a small group of R. cathartica.

(Picture: R.J. Koops)

Trioza remota is a rather common psyllid on the leafs of oak, Quercus robur and Q. petraea. At the upper surface a small pustule is visible where at the under side of the leaf is a small dimple with the nimph of the psyllid in its centre.