Fly fishing is such a broad discipline, and I never
want to loose touch with scientific side. So tonight, I’m writing a piece on
entomology, just for you! Lucky people… When you are ‘matching the hatch’ and
trying to dissect your targets feeding and behaviour habits, would you know a
Medium Olive from a Caddis? Or a Stone fly nymph from a March Brown? As I sit
here typing away, in enough entomology textbooks to even make Attenborough fall
asleep, it brings a full circle to my fly fishing. Time invested off the water
is just as valuable as time spent on the water, learning, discovering and
feasting your eyes of endless diagrams and pictures. Insects are the basis of
our sport, the foundations on which fly fishing was built, so I think they
deserve five or ten minutes.
Watercraft is an important part of all angling, but
especially when you’re chucking flies. It becomes a craft, a skill, an art, and
will quickly consume you. I’ve always admired Paul Procter’s writings and
work on the entomology side of fly fishing and really look up to his skill and
knowledge, hopefully one day i'll be an expert on aquatic insects too!
We’ll start with the humble yet beautiful, Medium
Olive – Baetis vernus. A small (no more than 25mm) nymph, they
swim in the water column occasionally holding on to debris. They are of the
order Ephemeroptera, which classifies all Mayflies, and can be readily seen on
many waters across the UK.
Baetis bernus during pupation |
Next on stage is the Blue Winged Olive – Baetis
tricaudatus. Another common species, also under the order of Ephemeroptera,
they are very similar to B.vernus although they do sport a
darker wing case and the terrestrials differ in appearance slightly. When I
studied this species last spring, my specimens showed a drastic case of sexual
dimorphism. This is where different genders of the same species develop
different attributes. In the case of B.tricaudatus males have
four compound eyes and females only have two, which is why some specimens
appear to have larger and red eyes (males). Pretty amazing stuff!
Baetis tricaudatus |
The sexual dimorphism shown by Ephemeroptera A) Female - 2 compound eyes B) Male - 4 compound eyes |
Staying within the Emphemeroptera order, this time
moving into the genus Mccaffertium. The March Brown (Mccaffertium
vicarium) is a ‘clinger’ nymph, and prefers to use its low profile to
hold onto the river bed or under the substrate. The dorso-ventral compression
(back and belly) creates a slim and aerodynamic body shape which is able to
hold on in the fastest of runs.
Now for the humble Caddis, everyone loves a Caddis!
From the charismatic case building to the angler-swarming hatches they create,
they’re an essential part of the river ecosystem and are a reliable bet for
nearly all still and moving waters. When in aquatic nymph form, they are best identified
by the material their case is built from. All Caddis’ come under the order of
Trichoptera. Take Microptera sequax for example, which is know
for building its case from sand grains which increase in size towards the case
opening. The actual Caddis inside used barbs on its body to hold itself inside
the case.
Limnephilus flavicornis is
another interesting example. Identified by its case, which is made from plant
debris arranged in a criss-cross fashion. On incredibly rare cases L.flavicornis has
been known to build its case entirely from tiny shells!
Limnephilus flavicornis |
There are also caseless Caddis species. The ‘net
spinning’ Caddis’ are covered by the two genera Hydropsyche and Cheumatopsyche.
These specimens build silk nets and externally attach materials for camouflage.
They carry out a rather unusual behavior known as behavioral drift, which is
where they leave the safety of their nets and drift to a new location, perfect
Trout food!
Net spinning Caddis - I have not been able to ID this specimen to species level |
Next I’ve decided to write about the Freshwater
Shrimp. Not an insect I know, but an important food item on the piscatorial
menu nonetheless! The only species found I England is Gammarus pulex.
English anglers maybe noticing more and more of these small crustacea
displaying an orange colouration, and this is due to a parasite. Parasitism is
pretty disgusting, but an incredible feat of evolution and should be respected.
The parasite affecting our little G.pulex is called Pomphorhynchus
laevis, and makes its host less photophobic, forcing the host to spend more
time out in the open and not in safe shelter under debris. This makes G.pulex an
easy prey item and consequently is easily taken by a fish, exactly what the
parasite wants as it then resides within its final host, the fish. So maybe
you’ll consider adding some hot spots to your shrimp patterns now!
Sialis lutaria |
So there you have it, a little entomology for you.
Hope you enjoyed it, and I hope it has enhanced your watercraft and bankside
knowledge because remember – catching isn’t everything. Please share your
knowledge in return using the comments! Whatever you’re up to this weekend -
fishing, tying, drinking.. make sure you smash it!
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