Spotting

What is strange is that during the day they are nowhere to be seen but every night, around 6 pm they regroup on that same plant again.

They look hungry!

that should read Dictyophorus

Try the family Pyrgomorphidae (foam grasshoppers) most of which are gregarious especially at the nymph stage. Look at the genus Dictyophus in particular - nasty creatures

Try the family Pyrgomorphidae (foam grasshoppers) they tend to display warning colours and to be gregarious, especially as nymphs. One common South African genus is Phymateus