Guest Blogger: Mary S. Kuss, Life-long avid angler, licensed PA fishing guide, founder of the Delaware Valley Women’s Fly Fishing Association

The insects that fish eat, and that fly fishers attempt to imitate or suggest, can be roughly divided into two main types: aquatic and terrestrial. Aquatic insects spend all or most of their lives in the water. Terrestrial insects are land-based and get into the water by accident. Whether they are blown in, knocked in, or just fall in, the fish are only too happy to eat them. It’s also very fortunate for both the fly fisher and the fish that during summer through fall, a time of year when not very many aquatic insects are hatching, terrestrial insects are at peak abundance.

All humans, including fly fishers or maybe especially fly fishers, are always seeking simple answers. But life in general, and particularly the community of insects that exists in and around bodies of water, is not simple. Rather it’s a messy and complicated thing, and seems determined to defy our notions of how its life forms might be classified and dealt with.

Fortunately, it’s not all that hard for the fly fisher to reduce this apparent complexity to something more comprehensible and manageable. First, we must abandon the notion that fish are always feeding selectively and that there’s one magical fly that’s necessary for our success. Opportunistic feeding is much more common, and this is particularly true with terrestrial insects. Most of the time fish are seeing a smorgasbord of terrestrials–a wide variety of sizes, shapes, and colors. It’s relatively rare for there to be enough of any one type to trigger the kind of selective feeding that occurs with concentrated hatches of aquatic insects like mayflies or caddis. So we can feel free to be a bit more fanciful in our choice of flies, without fear of failure or ridicule.

Let’s talk about some of the key factors that you should consider as you choose terrestrial patterns. Most fly fishers naturally tend to concentrate on familiar forms rather than the

photo by Paul J. Beel

off-beat, and there’s nothing wrong with that. Look at the terrestrial imitations in the bins at your fly shop, and you’ll find plenty of ant, beetle, cricket, and hopper patterns. Those are the Big Four, and with good reason—they work! You could use them to the exclusion of all other terrestrial imitations and do just fine most of the time. Remember, though, that fish in waters that get heavy angling pressure see an awful lot of them. It can sometimes be very productive to throw a change-up.

Keep in mind, too, the incredible diversity of these creatures. There are more different species of beetles than of any other type of insect. There is an incredible range of sizes, colors, and shapes within this group. Some are certainly more common than others, however. An acquaintance of mine was involved in cataloging the insects at a local State Park, and he told me that by far the most frequently captured specimen was a size 16 brown beetle. Need I say more? The common Lightning Bug is also a beetle, and there are flies made to imitate it. Ever see the ugly little segmented orange larvae chewing away on streamside willow shrubs? This is the immature form of the Willow Beetle. The adult is shiny black, oval in shape, about a size 20.

Are fish ever selective to specific terrestrials? Yes. The trigger for selective feeding, whatever the food item in question, is abundance. When one form dominates the available food supply, fish tend to focus on that form to the near-total exclusion of all others. This enables more efficient feeding. And no, the fish don’t reason this out with their little pea-sized brains. This behavior, which seems so perverse to us, is caused solely by instinct.

Note from J. Stockard: Parts 2 and 3 of the post will follow later this week.

1 Comment

  1. > The trigger for selective feeding…is abundance.

    This is a really good and really simple concept to keep in mind. Whatever may or may not be going on in a fish’s pea-sized brain that we cannot know, their behavior bears this simple thesis out. An angler who keeps such this observation in his own pea-sized brain could do far worse than to fish by it.

    Thanks, Mary, for another great tenet to keep in the frontal lobes.

    – Mike

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