Introduction to Fly Hatches
by
Eugene Macri
Aquatic and Environmental Scientist

In this introduction let's start off by talking about all the things you'll find at the bottom of the stream.  Perhaps we should describe the bottom of the stream:

• All of the rocks, many of the plants (macrophytes and algae), debris, wood, gravel, sand etc. are referred to as substrate. So aquatic invertebrates live on or around the substrates of a stream or river. 
• Invertebrates are animals without backbones.  Invertebrates that have 6 legs are referred to as insects. There are other things in this invertebrate community such a freshwater shrimp, scuds, cressbugs, crayfish and worms that do not have 6 legs and therefore are classified as something else. 

Classification Systems

Now why do scientists (mainly biologists) classify things?  Simply put: it makes things easier to study. Nature doesn't classify things but man does.  Another thing you should know that we will get into much later is that classification is an arbitrary science and not all biologists will agree with classification, taxonomy and nomenclature (the naming of the insects). Here's one of the more popular classification systems used by biologists today:

 * (Domain)
  o Archaea
  o Bacteria (also called Eubacteria)
  o Eucarya
    * Kingdom
  o Animalia
  o Plantae
  o Protista
  o Monera or Procaryotae
  o Fungi
    * Phylum
    * Class
    * Order
    * Family
    * Genus
    * Species

It should be noted that the above classification system is not accepted by all biologists.  In the above system The Domain Eucarya refers to organisms with true nuclear cell structure.  As you can see the kingdom Animalia is under this and this is where the insects and stream invertebrates reside.  Most of the invertebrates on the stream bottom belong to the Phylum Arthropoda (which means jointed appendages).  As you go down the tree the categories get more specific and thus you eliminate organisms till you get to the individual species.  There are many subdivisions to the above categories but we don't need to go there because if you just recognized how this works, it's more than enough to understand the beginnings of aquatic entomology.

Every organism has a name, a scientific name that is. The name is in Latin or Latinized as some might say. It usually consists of two parts, Genus and Species, called binomial.  This distinguishes it from the common names which are often local and confusing.  Sometimes the name can be made up of three parts and then it is a trinomial.  Sometimes the scientist who named it or someone who first discovered it will give it his or her own name of someone else's.  For example, one of the mayflies known as Blue Winged Olive has a scientific name of Baetis tricaudatus Dodds.  In this case Baetis is the Genus; tricaudatus is the species and the Dodds is the name of a biologist associated with it.  In most cased the Genus is capitalized and species is not.  They are either italicized or underlined.

Here are some examples of some flies that fly fishermen use with their common and scientific names:

• Sulfurs, Early Morning Sulfurs, Blue Winged Dun Orange Sulfur, Early Season Sulfur, Late Season Sulfur Pale Morning Dun. Pale Eveining Dun: Ephemerella invaria, Drunella lata etc.

Seems confusing isn't it. That's why scientists and some fly anglers refer to the Latin names because the common names vary so much by location and their is no standardization. So the Latin names are nothing more than a "standard" that all scientists can use no matter what language they speak. So if someone tells me it's a sulfur... but then says it's an Ephemerella etc.....I now know what he's talking about. Latin is a dead language because it doesn't change and isn't influenced by the time, fads, or culture and thus serves scientists very well as the standard way to describe an organism that will be universally accepted no matter what language the scientist speaks. Here's an example of the identification of the brown trout.

So why does the brown trout have two scientific names. Well because in some texts the brown trout is often given the name Salmo trutta fario, the brown trout of small streams. This a trinomial or 3 part name. Is this a distinct subspecies....ok now I got you because you want to know what a subspecies is? So that's my point. Just understand the basics and don't worry about stuff like this; wait till you get a better understanding of the entire system then you can go deeper into how things are classified.

Life Cycle of Aquatic Insects

Aquatic insects are like terrestrial insect in that they undergo a life cycle.  Remember insects are Arthropods and must shed their exoskeleton to grow in a process known as molting (humans have an endoskeleton and grow around it).  Each mayfly, stonefly, caddisfly etc. has it's own individual life cycle of molting depending upon environmental conditions.  The changes of the life cycle are known as metamorphosis.  In America we differentiate two types of metamorphosis: Complete and Incomplete. Examples of this are shown below:  

The stages in a complete metamorphosis are egg, larva, pupa, and adult.  In incomplete metamorphosis the stages are egg, nymph, adult.  Examples of insects with complete metamorphosis are caddisflies, and butterflies. Examples of insects with incomplete metamorphosis are mayflies, and dragonflies.  In most European and Asia texts however, and for the most part in the world of entomology all immature stages are referred to as larvae (larva is singular).  This is a common mistake many American fly fisherman make when they read descriptions from other countries since they refer to mayfly and dragonfly nymphs simply as larvae. Insects actually "hatch" out of eggs.  Matching the hatch should actually be referred to as Matching the Emergence since aquatic insects emerge as adults.

This completes your introduction to Aquatic Entomology so let's summarize what we've learned:

Summary: Aquatic insects are invertebrates that undergo a life cycle of metamorphosis in which they change from egg to adult.  Most aquatic insects live on, or in the bottom material of a stream or substrate. Scientists classify organisms to make them easier to study and understand. The classification system of Taxonomy is an arbitrary standard agreed upon by most biologists.  They have assigned every living organism a scientific name which is written in Latin.  This name consisting of Genus and a Species is often called binomial nomenclature.

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