Terrestrials tumble into rivers and waterways throughout most of the prime angling season. While hoppers are associated with late summer and fall, ants and beetles are active whenever temperatures are warm enough to get their metabolism moving. Terrestrials can be very effective for challenging hatches, when a more precise imitation may not clinch the deal.
Given these advantages, a terrestrial fly box might hold a good mix of these flies. All will consistently put that bend in your rod we all hunt for.