What they are
Land insects, not water insects, and that is the whole story. A grasshopper on the water is an accident: it jumped or was blown there, it cannot get off, and it is the biggest meal a stream trout will see all day. Trout learn this fast. Within a week or two of the hoppers appearing on the banks, the fish move to the grassy edges and hold there in the afternoons, and a well-placed imitation is taken with a confidence you rarely see on a mayfly.
No Latin names are needed. Size and colour matter a little; where the fly lands matters a lot.
When and where
On the Monaro and through the Snowy Mountains the hoppers come up on the tussock flats from late December and stay until the April frosts thin them out. Warm, windy afternoons are the best of it: the wind blows them off the grass and onto the water, and the fish know it. Mornings are quieter until the day warms and the insects start to move.
The water is any river or creek with a grassy bank. On the Eucumbene that is the tussock plain above Kiandra, the flats around Denison and Providence, and Nimmo Plain below the wall. This guide's own experience on the Monaro-fed tributaries is that the fishing keeps paying well into autumn.
How to fish it
Tie on a hopper sized to the grasshoppers you see, and fish it within a rod length of the bank. Let it land with a plop. Leave it. If nothing comes in the first few seconds, one small twitch, then a dead drift to the end. Cover the undercut bends and the grassy edges, not the open middle of the pool.
Before the hoppers are moving, hang a small nymph under it and fish the dry-dropper until the afternoon wind arrives. When the fish start refusing a hopper on low clear water, drop a size or change to a small quiet dry; they are still eating, they have just seen too many.