These huge ants (#10-12's) are the first of the Truckee's "Big Bugs of June" to make an appearance locally. Now we're looking for the other two Big Bugs; Western Green Drakes and Golden Stoneflies. Both adults can be "phantoms"; most especially the Drakes.
June is an angler's first chance of "searching" the water and hooking a large trout at the surface.
All the stream occupants are aware of and on the look-out for the Big Bugs, and the opportunity to ambush such high-caloric meals. The Truckee's out-sized trout in the 18"-25" range, are known to leave the bottom and eat aggressively on top...most of the time. A client once had the rare exception of a subtle take; on the flat-water of the LT's Bluff Slick. A perfectly dead-drifted #8 Green Drake Quigley-Cripple simply disappeared, sucked-down and absolutely no water displacement.
And since I've mentioned a "water-column", rest assured, dislodged large nymphs of both of the Golden and the Drake are ALWAYS eaten. Remember the Goldens have a 2-3 life cycle; making them readily available during their progressive instar-growth up to a size 4. Fishing the Drake nymphs (#'s 6-10) are most productive prior to their emergence since most of them migrate towards the shallows and quiet water in lieu of clinging to the bottom in heavy water. As for the huge Black ant (winged or wingless); fish it dry or sunk (HINT).
Attractor/impressionistic patterns of all three Big Bugs are sufficient to dupe the trout.