Planthopper

Planthoppers are insects in the infraorder Fulgoromorpha. They are true bugs (Hemiptera), with over 12,500 described species. 
They are cryptic mimics: their body shape and colours look like leaves and other plant parts in their environment. They either walk very slowly or hop like grasshoppers. 
Members of this group are plant-feeders, and live world-wide. Few are pests, but some are vectors for plant diseases. Phytoplasmas which live in the phloem of plants can be transmitted by planthoppers when feeding.
Their nymphs have a biological gear mechanism at the base of the hind legs, which keeps the legs in synchrony when the insects jump.
In popular culture.
The planthopper is mentioned in a key scene from Alfred Hitchcock's film "Marnie":