It's the middle of a hot July afternoon. The morning hatch ended hours ago, the river has gone quiet, and most anglers are either walking back to the truck or standing in the run cycling through mayfly patterns that stopped coming off the water at ten in the morning. It looks like the fishing's over for a while.

It's not. A whole food source is working the entire time, and it reaches the fish by falling onto the water instead of hatching up through it. A grasshopper clatters out of the grass, an ant tumbles off a branch, a beetle misjudges the wind. Summer is terrestrial season, and once the aquatic bugs thin out in the heat, the trout that are still eating have turned to the bank.

Why summer trout turn to the bank

A terrestrial is any land insect that ends up in the water by accident. Grasshoppers, ants, beetles, crickets, the occasional inchworm. These bugs live in the grass and brush right up to the edge of the water, and through the summer a steady number of them are always falling, hopping, or getting blown in.

That steady drip off the bank adds up to a real shift in what trout eat. Ecologists call the land insects that wash into a stream a terrestrial subsidy, and it peaks in summer and drops to near zero in winter. In one closely studied stream, terrestrial insects made up between 50 and 90 percent of the fish's diet during the summer and close to half of the whole fish community's energy intake for the year. A multi-year study of brook trout estimated terrestrials at 38 to 47 percent of everything the fish ate by weight over a year, and an even larger share of the energy they took in, because these are big, high-value bugs. The shift lands in summer for a plain reason. Warm water and long, bright days push the mayfly and caddis activity to the cool edges of the day, so through the long middle of the day the most dependable meal on the river is whatever wanders off the bank.

That's the appeal. These are large, high-calorie bugs, and a trout will move a long way and eat one with real confidence. A fish sipping tiny mayflies can be maddening, but one that's decided grasshoppers are on the menu will crush yours, often right on top where you get to watch the eat.

Hoppers, ants, and beetles: the three that matter

You don't need a fly for every land insect. You need to cover three shapes.

Grasshoppers are the headline act. They overwinter as eggs, hatch in late spring, and grow through the summer, so the big adult hoppers a trout wants are most available in the warm middle and late part of the season. That's when to fish them. The best hopper days are warm and breezy, once the grass is tall and the bugs are grown and clumsy.

Ants are the quiet killer, and they're more effective than most anglers give them credit for. Ants carry formic acid, which is where the family name Formicidae comes from, and trout seem to key on them out of all proportion to how many are actually in the water. Stream studies have found that ants show up in trout stomachs at a higher rate than they show up in the drift, which is a technical way of saying trout go out of their way to eat them. They're small and hard to see on the surface, so most people ignore them, but a fish will take an ant with total confidence. Watch for a flying-ant fall, too. Winged ants leave the nest to mate in big coordinated swarms on warm, humid days, often right after a summer rain, and when a batch of them ends up on the water you can get some of the best dry-fly fishing of the year.

Beetles are the great all-summer searching bug. Beetles make up the order Coleoptera, which is the largest order of animals on earth, with something like 400,000 described species and close to 40 percent of all known insects. There are beetles everywhere, all summer, which is why a beetle pattern is almost never a wrong guess even when you don't see one on the water.

As with matching any hatch, silhouette and size matter far more than the exact pattern. A trout keyed on ants wants a small dark ant shape and doesn't care whose ant it is. Get the outline and the size close, put it where the naturals are landing, and drift it clean.

The hopper-dropper, the summer workhorse rig

If you fish one rig all summer, make it a hopper-dropper, because it answers two questions at once. You tie on a big, buoyant hopper or foam terrestrial as your top fly, then hang a nymph off the back of it on a length of tippet tied to the bend of the hook. The hopper is a real target the fish can eat and a strike indicator at the same time, and the nymph rides below for the fish that aren't committed to looking up.

Start with the dropper somewhere around 18 to 36 inches, short and shallow, and lengthen it to get deeper if the top fly gets ignored. The rig itself tells you what the fish want. If they keep eating the hopper, you can go bigger or add a second dry. If every take is on the dropper, they aren't looking up yet, so fish the nymph deeper or heavier. The rig is a question you ask the river, and the fish answer it.

This is the point where it helps to know what the day is actually shaped like on your water. Rivus reads your river's live temperature, flow, and the season and tells you when the terrestrial window is on, and just as important, when the water is warm enough that you should be careful with the fish. Where there's no live gauge nearby it labels the read as an honest estimate instead of inventing a number, and Eddy can talk you through whether today's a warm hopper afternoon or a fish-at-first-light morning.

Where to fish terrestrials: the bank and the grass line

Because terrestrials come from land, the fishing is a bank game. The best water is often the strip nobody casts to, the foot or two right against the shore, under overhanging grass, below a cut bank, tight to a fallen log or a line of brush. That's where the bugs go in, and that's where the fish sit waiting for them. Drift your fly right down the grass line, close enough that you occasionally hang it in the weeds, because that's exactly where the naturals are landing.

Wind, which everyone curses, is a gift here. A stiff breeze knocks hoppers and beetles off the vegetation and onto the water in bunches, and a windy bank is often the most productive water on the river in late summer. Watch the downwind shore especially. And don't wade past the near bank to reach the middle. In terrestrial season the fish are frequently holding right where you'd have stepped in.

Let it land with a plop

Terrestrial fishing rewrites the delicate-presentation rule you learned for mayflies. A real hopper doesn't settle onto the surface like a snowflake. It hits with a small plop, and that little disturbance is a dinner bell. Don't be afraid to let a hopper land with a soft splat a foot off the bank, and give it the occasional subtle twitch to imitate a struggling bug trying to get free. Keep the dropper honest, though. The nymph underneath still wants a drag-free drift, so twitch with intent and then let it ride, rather than turning it into a constant retrieve.

The honest part: a warm-hour game

Here's the catch that the fun of it can make you forget. Terrestrial fishing peaks in the warm middle and afternoon of a summer day, which is the exact window when the water is warmest and hardest on trout. The same water-temperature read that governs all summer fishing still applies.

Around 68 degrees Fahrenheit, warm water starts to hold too little oxygen for an exhausted fish to recover, so a trout you fight and release on a hot afternoon can die hours later even if it swims off looking fine. A recent review of the science argues for being more conservative than that, closer to the low 60s for rainbow, cutthroat, and brook trout. Fisheries managers act on the same math. Montana closes many of its rivers to afternoon fishing, from 2 p.m. to midnight, once the water hits 73 degrees for three days running, because water in the mid-70s and up can be lethal to trout.

So on low, warm water the honest play is to fish terrestrials early, in the cool and the bank shade, and to back off when the temperature climbs into the range where a release stops working. The bugs will still be there next week, and so will the fish, if you let them be.

Terrestrials are proof that the summer slow spell is mostly a myth. The trout are still eating. They just moved to the bank while everyone else went home. Learn to fish the grass line, and August stops being the season you tolerate and becomes one of the best windows of the year.