During late summer and early fall, fewer and fewer insect hatches remain, and the prolific emergences of spring and summer are only a memory.  What do fish feed on during this hotter, drier time of year?  The answer is terrestrials, land insects and a wide variety of them.

Stream banks, shorelines and nearby uplands present many habitat types, each with their own array of non-aquatic insects.  Because of their proximity to water, there's the chance these individuals will become part of the aquatic food web.  They simply have to be shaken from a leaf, hop indiscriminately, or be blown off course while flying to land on the water's surface and become available to a hungry fish.

Adding to the characterization of this potential predator-prey interaction is the fact that these insects are not at home in the water.  They tend to remain on the surface, floating and drifting enticingly over waiting (and hungry) fish. They lack the necessary anatomical and physiological mechanisms to permit efficient diving below the film, but they may be churned under by turbulent water. 

Because they aren't efficient swimmers, like true aquatic organisms, they may make awkward movements.  Application of these features translates into a convincing surface or subsurface drift and/or the appearance of struggling activity that can nicely complement use of the right artificial.

Fly fishers traditionally have focused on imitation of a limited number of productive terrestrial life forms, because of 1) the probability they will be on the water during the late season and 2) resultant successes generated by their imitation.  These include the grasshoppers (and their relatives, namely crickets), ants, and, to a lesser extent, beetles and leafhoppers.  Only one of these groups, the beetles, actually has aquatic counterparts.  This might appear to complicate the situation if it weren't for a basic similarity in appearance of water and landforms that allows successful imitation to be accomplished with variations in a common artificial shape.

Just some of the possible players in the "smorgasbord of terrestrials" (terminology descriptively used by Jim Humphrey and Bill Shogren in their book Trout Streams of Wisconsin and Minnesota) follow.  None of these insects is particularly obscure, but a few reminders might be helpful:

Grasshoppers and crickets are related members of the order Orthoptera.  Adults of these insects are characterized by straight wings and legs modified for jumping.  They occur in a variety of colors.  Metamorphosis is simple, so the primary visible differences between immatures and adults are body size and wing length.  Small wing "pads" on the very young are replaced incrementally with each juvenile molt until they reach full size.

Ants are relatives of the bees and wasps (order Hymenoptera).  They have three distinct body regions with a conspicuous thin "waist" between the thorax and abdomen.  Elbowed antennae are also characteristic.  Ants are social insects with complete metamorphosis.  The only life stage commonly seen is the adult, which can vary in size (up to ½ inch in length) and color.  Ant colonies can produce large numbers of progeny making individuals extremely numerous at times.  Gary Borger in his excellent resource titled Naturals emphasizes the way ants float "down in the film" and that they commonly become submerged.

Because probability plays a role in terrestrials on water, it's good to know that close to 40 percent of all insects are beetles.  The order Coleoptera to which they belong is characterized by thickened and leathery or hard wing covers (elytra) that meet in a straight line down the back.  Aquatic beetles tend to inhabit standing water and slower regions of streams but terrestrial forms can be on the surface anywhere, anytime.

Leafhoppers are relatives of the true bugs and are classified with them in the order Heteroptera, or separately as the Homoptera.  These are common plant-feeding insects up to ½ inch in length; many are smaller.  Adults have two pairs of wings with the front pair covering the back; wings are held roof like at rest.  These insects are known for elaborate coloration and patterns.

Excellent possibilities exist for imitations of these incidental insects.  Shapes, sizes, and colors vary for each and all-important movement (i.e., behavior) is critical for successful use.  During the late summer, it's always a good idea to determine the presence of standard late-season aquatic insect hatches, looking, for example, for caddis, baetids, and midges taking flight.  And then it's highly recommended to simply screen the surface and subsurface of fishable water to identify the presence of terrestrial insects in an aquatic (stream) food web. 

In the end it's important to appreciate that not everything that's in the water is of aquatic origin, and recognition of this fact may play an important role in our pursuit of trout.

Clarke Garry earned a PhD at the University of Wisconsin/ Madison and taught at the UW/ River Falls until retiring. His column appears in every issue of Midwest Fly Fishing magazine.