A Bug in the Hand Beats Two in the Bush

When it comes to fly design it helps to have a good idea of what the actual bugs looks like. Being able to take your time to really assess the shape and color of an aquatic insect in its natural environment gives the fly tier a big advantage. But most bugs rarely sit still for very long, and aquatic larvae removed from the water tend to look darker and more clumpy than they actually are. A bug in the hand may beat two in the bush, but a good photo trumps them both.

A Dragonfly darner nymph (Aeshna sp.). You can tell that this one has
more growing to do by the small wing-pads.

A Dragonfly sprawler nymph (Cordulia shurtleffii)
This one has fully developed wing-pads and
is ready to emerge.

This is what Cordulia shurtleffii looks like as an adult. Its metallic-green eyes earned this
species the common name of American Emerald.

An adult Variable Darner (Aeshna interupta) laying eggs in a rotten log.

Weaving a Deception

I have been working on some woven-body dragonfly nymphs this week. Reg Denny taught me how to do this many years ago. It makes for a very realistic looking abdomen on any dragonfly pattern - including the longer and darker darner type patterns. The first one imitates the stubby sprawler type dragonflies during the spring pre-hatch migration.

A short, stubby woven dragonfly sprawler imitation.

I'm one of those tiers who doesn't always follow a recipe - most of the time I just wing it by memory. This dragonfly patterns start with two lengths of lead free wire laid along either side of the hook shank - this gives the body a somewhat wide and flat appearance like the naturals. Leave enough head space to attach the eyes. The hook for sprawlers is usually a 2XL #8 to keep the fly short and stout. I do up a bunch of the hooks with wire ahead of time and make sure the wire is tied down well and add a little head cement to keep it all in place. 

The weave is an alternating over & under using two strands of yarn in slightly different colors - one color for the dorsal side and one for the ventral. If I haven't tied them for a while it seems I need to re-learn the technique and practice a bit before I start on the actual flies. There are a few YouTube videos out there that cover the woven body technique better than I can explain it. My preference is for soft legs using tufts of dyed mallard flank - this allows the legs to sweep back when using a darting retrieve. The thorax is not woven - just a simple wrap spaced to keep the legs in position. I used bead-chain for the eyes on these ones but I also use glass beads on heavy monofilament with the ends melted sometimes. The wing case is traditional turkey quill. Colors for the sprawls range from light olive to olive-brown.

A longer-bodied woven dragonfly darner imitation.

The darner pattern is tied on a 4XL #8 hook using two strands of brown yarn in slightly different shades. Fine "nymph" rubber legs have a good action on the larger fly. Make sure to make the abdomen longer relative to the thorax  for this one.

Emerging Dragonflies - a video & photo essay

Dragonfly hatches are a big draw for larger trout. But many fly anglers fail to notice when a hatch is in progress, or realize that the nymphs will start migrating towards shore in the days leading up to a hatch. If you don't know what to look for, or how to properly work your fly, you are missing out on one of the best hatches of the spring trout season. This short photo essay will bring you up to speed.

Knowing what happens under water during a pre-hatch migration gives the fly angler a big advantage when fishing a dragonfly hatch. This older, low resolution footage shows how the nymphs make their way to the shoreline, using a combination of crawling and swimming. 

A dragonfly nymph (Epitheca spinigera) fresh out of the water and
making its way up shoreline vegetation in search of an emergence site.

It is not easy wiggling out of the nymphal exoskeleton - gravity is used to aid in the process.

Once free, it can take up to an hour for the body and wings to fully extend.

Wings and body starting to take shape.

Almost ready to fly - the wings just need to harden a little more and extend out to the sides.

A close-up of the large compound eyes.

As soon as the adults can fly, they make their way to nearby trees or bushes to
rest and allow for any final hardening to take place.
(Spiny Baskettail - Epitheca spinigera)

Adult dragonflies are very territorial - but during a heavy hatch they will congregate on lake-side shrubbery for a bit as they soak up some sun and complete the hardening of their exoskeleton.
There are 18 adult dragonflies in this photo.

Cased Chironomid Larva Respiration and Movement

In my last post I talked about how chironomid larva that build tubes or cases use body undulations to maximize oxygen intake. This behavior is used by not just chironomid larva living in the hypoxic zone on the bottom, but also by chironomid and caddisfly larvae that build portable cases. They do this when  oxygen levels are low or they need to refresh the stagnant water in their case. 

This video shows how a chironomid (midge) larva undulates in its tube to circulate water to aid in respiration. This particular genus (Cricotopus) builds a portable tube, while other chironomid groups construct more extensive stationary tubes in the mud. The video also shows how chironomid larvae that build portable tubes move by reaching out and pulling themselves forward. In the final scene, the midge larva gets caught on a strand of vegetation and uses a small pebble to leverage itself up and over.

Midges, Hypoxia, and Hemoglobin

Note: This post may not make you a better fly angler, but it will make you a more knowledgeable one.

One of the pitfalls of living in the mud at the bottom of a wetland or lake is that there can be very little oxygen present. Oxygen diffuses much slower through water than it does in air, and even slower through the mud barrier where the decay of organic debris further depletes what little oxygen is present. Under these low oxygen (hypoxic) conditions, life is limited to organisms that are adapted to survive in these extreme environments.

Some chironomid (midge) larvae have adapted to exploit these hypoxic habitats through the use of hemoglobin. Hemoglobin is the protein component of red blood cells that circulates through our body and is responsible for delivering oxygen to tissues. It also gives blood cells their red color. Hemoglobin has a high affinity for binding to oxygen molecules making it the perfect oxygen delivery system where constant circulation is present.

There are several groups of chironomids that utilize hemoglobin to aid in survival under hypoxic conditions, but the two most common ones are in the genera Chironomus and Glyptotendipes (commonly known as blood-worms). The high concentration of hemoglobin in their body fluids (hemolymph) gives them their distinctive red color. While there can be some passive movement of the hemolymph through their body, it does not circulate like our blood does. Instead, it simply surrounds the organs and tissues.

Note that more evolved and larger insects may have an open circulatory system, but even here, the hemolymph does not circulate very fast and oxygen uptake and transport is primarily via the air-filled tracheal system.

A Chironomus larva with its typical bright red coloration.

So how exactly does the hemoglobin help blood-worms survive in hypoxic and sometimes anoxic (no oxygen) habitats? If there is little to no oxygen to bind to the hemoglobin to begin with, what advantage can there be?

Most blood-worms build extensive tube networks in and on the mud by tunneling and reinforcing the tube walls with mucus. These tubes provide protection from predators but they also allow the midge larva to circulate water through the tube by undulating its body within the tube (caddisflies also do this). This action pulls water with a slightly higher oxygen content through the tube. In some cases, the midge larva will also elevate the tube opening, even by just a few millimeters, to place the tube intake above the low oxygen boundary layer at the water-mud interface. Of course under low oxygen conditions they can't spend all of their time undulating to gain oxygen, they need to feed too. That is where the hemoglobin comes in - as the larva undulates and circulates water through the tube, the hemoglobin picks up oxygen (much like recharging a battery) - then when the larva stops undulating to feed; oxygen bound to the hemoglobin diffuses into the tissue to sustain metabolic activity. Once the hemolymph oxygen level falls to a critical point, the midge larva will once again take up its ventilation position in the tube to recharge its oxygen supply.

A Glyptotendipes larva out of its tube and foraging for food.

This species of Glyptotendipes builds its tube out of mucus and bits of organic debris. Here, it has chosen to establish its tube up in the vegetation rather than on the bottom. Note the red and bright green coloration – this is the impetus for the midge fly pattern known as a Christmas Chironomid.

Deep Water Chironomids Feeding and Swimming

The most productive part of a lake is the littoral zone where the penetration of sunlight allows for the rapid growth of aquatic plants and periphyton. Here is where you will find the highest level of bug biodiversity, including a hundred or so species of chironomid (midge) larvae. But this doesn’t mean that the deep water areas of a lake are devoid of life. In fact, there are some genera of chironomids (Chironomus and Glyptotendipes) that specialize in hiding in the low-oxygen layer of mud during the day, and coming out at night to forage for whatever tiny organic particles of food they can find.

While the diversity of midge larvae living in the mud 15 to over 60 feet down is low, the biomass (number of organisms) can be very high. This is because, with very little oxygen to support life in the hypoxic mud layer, there is little competition for food. The midge species that can live in this layer of mud are able to monopolize on the resources, much like the mono-culture of a wheat field.

One would think that there is not much to eat way down there in the depths, but as organisms living in the upper layers of the limnetic zone die (algae, zooplankton and cyanobacteria), or organic bits get blown onto the lake’s surface (pollen and organic dust), they settle to the bottom. This translates into a continuous shower of food for most of the year, even in the deeper parts of a lake.

This video shows midge larvae foraging for food on the lake bottom and their swimming behavior when they decide to move longer distances to find better foraging sites. Their swimming behavior is unique, and somewhat frantic, and not easily imitated by the fly angler.

The Curved vs. Straight Debate

 Every fly tier who frequently fishes scud patterns has an opinion on this; should scud patterns be tied on straight shank or curved shank hooks?

Scuds at rest tend to have a very pronounced curve. This observation has resulted in a large number of scud fly patterns being tied on radically curved hooks – what used to be called scud or shrimp hooks.

A Scud (Gammarus lacustris) in a typical resting position.

But scud patterns are generally fished with some sort of retrieve – imitating a scud in motion. Scuds actively swimming tend to straighten out their bodies to become more streamlined. In this situation, a scud pattern tied on a straight hook makes more sense. But do swimming scuds really hold their body as arrow-straight as a straight shanked hook? The answer is a definite no. While the degree to which a scud holds its body straight while swimming varies, the telson and last few body segments generally curve down a little, and there is usually a slight curve along the back (seen in the photos below of scuds actively swimming).

So what is the best hook for a scud pattern? You certainly want to avoid the radically curved shrimp hooks. But I am not sure it matters much if a scud pattern is tied on a straight or slightly curved hook. I have done both over the years and find them equally successful. When I do use a straight hook, I tie the body slightly onto the bend of the hook to simulate the turned down telson and last few segments. My preference now is to tie scud patterns on slightly curved pupa hooks. I consider it a compromise when fishing the fly with short slow strips followed by a pause - straight enough to fool the fish on the strip and also curved enough to look natural on the pause.