These are the immature stage (nymphs) of the Four-lined Plant Bug (Poecilocapsus lineatus) in the family Miridae (Hemiptera).
The dark brown marks on the leaves are feeding damage. The eggs are also laid inside slits made in plant stems, which cause further damage. Though most well known for feeding on members of the Mint family (Lamiaceae) and Daisy Family (Asteraceae), Poecilocapsus lineatus also feeds on many other plants, such as Crane's-bills (Geranium spp.)