Terrestrial Beetles come in
all colors and sizes. This one
is huge. These large beetles
are fairly common in the park.
Terrestrial Insects: (Grasshoppers, Ants, Beetles, etc)
.........................            ..... ...Fly Fishing Yellowstone National Park
Usually when you find flying
that have landed on the
water, you will find a lot of them.
Terrestrial insects are insects that are born and spend most of their life on
land. They get into the water only by accident. Windy conditions and other
natural conditions can cause these insects to sometimes loose their
caution and end up becoming a meal for a trout.

It would be a rare occasion that trout ever became selective on any
terrestrial insect. It would be possible during a flying ant fall, or possibly
when a large amount of ants or beetles were washed into the water by
heavy rains or high winds. This means that most all of the time, the trout
are just looking for something to eat on the surface of the water. They do
not recognize the various types or species of terrestrial insects that may
come floating by. The strictly feed opportunistically on them. When there
are few insects on the water trout are likely to take every insect that comes

If a large amount of any one insect became available over a period of time,
then it would be likely that the trout would search only for that insect or feed
selectively on it. When this happens, they begin to settle into a steady
feeding rhythm and focus on individual insects. Facts are, it would be rare
that enough terrestrial insects fell, blew or got washed into the water to
cause selective feeding.

Imitations of Terrestrials: (Flies)
This means that you can get by with, except for a few rare exceptions,
fishing an imitation of any terrestrial insect you desire to imitate.  As long
as it is something of the size and shape of an insect, the fish will see your
fly as something to eat. Their brain isn't large enough for them to be able
to identify it as something they saw last year at the particular time of the
year. They they don't need to be able to do so in order to survive. They may
eat a beetle one minute and a grass hopper a few minutes later.

If the fly sinks, it will probably get more takes from trout than if it floats
beautifully on the surface. Most ants, beetles and hoppers that fall into the
water slowly sink.

These are some of the more plentiful and common terrestrial insects that
get into the freestone streams of Yellowstone National Park.

The most common terrestrial insect in the park is the beetle or
Coleoptera. There are both aquatic and terrestrial forms of beetles but
here we are concerned with the terrestrial form.  Some species of beetles
can fly and these are more likely to get into the water than the others that
cannot fly. Overhanging limbs of trees, grass and shrubs provide the
places for beetles to fall into the water.

Ants, the Formicidae family of insects,  is one of  the next most plentiful
terrestrial insect found in the park. Fast rising water caused by heavy rains
is responsible for ants and terrestrial beetles getting into the water more
than anything else. Ants live in colonies and when they do get washed into
the water, they usually do so in large quantities.

Some ants can fly and these
flying ants can easily end up in the water.
When they do, they are usually preyed on by trout in a feeding frenzy.
These great swarms of arts perform their nuptial flights, the winged males
or drones, die shortly after they swarm. If the flight of ants happens over a
stream they fall in the water and usually just carpet the water. Don't stand
around waiting for this to happen, you may grow old waiting. But if you find
flying ants falling in the water, the trout will usually go nuts. Be prepared for
a flying ant fall. They usually occur during the late summer months.  

Grasshopper exist on every stream in the park but they are not as plentiful
in the forest as they are in the streams that flow through meadows and
open areas where high grass exist.

Wherever you find banks with lots of grass there most likely are lots of
grasshoppers. Grasshoppers become important starting in July but much
more so in the latter part of the Summer and early autumn. They are apt to
get into the water much more so on windy days.

Bees and Wasp:
Bees live in colonies. These colonies are usually very large and contains
thousands of insects. They sometimes fall into the water.

Copyright 2012 James Marsh
Flying Ants: This is one of
thousands that fell into the
water of the Lewis River in late
August. You should always
have a few flies ready  for them.
Big grasshoppers can be
found in all the meadow
streams of Yellowstone as
well as other types streams.
They are present in less
quantities in wooded areas.
This beetle was crawling along the banks of
the Gibbon River. I tossed it in the water and it
was gone in a flash.
The high grass has all colors of
grasshoppers. I doubt the color makes much
difference in this location.
These large brown grasshoppers are
The green grasshoppers blend in very well
in the high grass. When you walk through
the grass the hoppers flyin all directions.
They have no idea what's about to happen
to them when they hit the water.
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