Field Guide to Freshwater Invertebrates of North America

Field Guide to Freshwater Invertebrates of North America

by James H. Thorp

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The Field Guide to Freshwater Invertebrates of North America focuses on freshwater invertebrates that can be identified using at most an inexpensive magnifying glass. This Guide will be useful for experienced nature enthusiasts, students doing aquatic field projects, and anglers looking for the best fish bait, lure, or fly. Color photographs and art, as well


The Field Guide to Freshwater Invertebrates of North America focuses on freshwater invertebrates that can be identified using at most an inexpensive magnifying glass. This Guide will be useful for experienced nature enthusiasts, students doing aquatic field projects, and anglers looking for the best fish bait, lure, or fly. Color photographs and art, as well as the broad geographic coverage, set this guide apart.

  • 362 color photographs and detailed descriptions aid in the identification of species
  • Introductory chapters instruct the reader on how to use the book, different inland water habitats and basic ecological relationships of freshwater invertebrates
  • Broad taxonomic coverage is more comprehensive than any guide currently available

Editorial Reviews

From the Publisher
"IAN'S RECOMMENDATION: For anyone interested in the freshwater animals of North America."—-The Guardian’s Punctuated Equilibrium

"The strength of this text lies in the narratives describing the form, function, ecology, and collection methods associated with each major group. Consequently, the book is more of a primer or an introduction to freshwater invertebrates, than a field guide. Summing Up: Recommended. Lower-division undergraduates and general readers."—Choice, September 2011, Vol. 49, No. 01

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Field Guide to Freshwater Invertebrates of North America

By James H. Thorp D. Christopher Rogers

Academic Press

Copyright © 2011 Elsevier Inc.
All right reserved.

ISBN: 978-0-12-381427-2

Chapter One

Using This Book Effectively


A. What is the Nature of This Book?

Aquatic ecosystems contain an amazing diversity of invertebrates. Whether one is exploring a creek or river, a pond or lake, or even more unusual habitats such as vernal pools and water-filled tree holes and depressions in rock outcrops, you are bound to find bugs, wrigglers, rattails, snails, clams, mussels, elktoes, pocketbooks, mud bugs, crawdads, toe biters, hellgrammites, bloodworms, punkies, drakes, bloodworms, and many of varieties of small animals known collectively as invertebrates. This guide is designed to assist you in identifying the small aquatic animals that you may find living in freshwater (nonmarine) habitats.

Many of these organisms remain unseen due to their small size and secretive habits or are even ignored because identification is difficult. The invertebrates most commonly noticed are flashy or colorful (some crayfish, mussels, and beetles), good fishing bait (hellgrammites, caddisflies, mayflies), tasty (crayfish, shrimp, crabs), or an occasional painful nuisance now or later (toe biters, creeping water bugs, larval mosquitoes). However, with a little exploring, one can find an incredible array of aquatic invertebrates living under stream rocks, swimming in shallow pools, or hiding among plants in the margins of lakes and rivers.

Very few of our aquatic invertebrates can bite or pinch a human, and none can sting or poison you. Many of our aquatic invertebrates are important indicators of water quality and habitat health. All the water bugs, snails, crayfish, mussels, and worms have important functions in processing organic material, controlling algae, and feeding fish, birds, turtles, otters, and raccoons.

This book is divided into three parts. Part I (Chapters 1 and 2) introduces the organisms, provides information on collecting invertebrates, and describes the process of identifying invertebrates. Chapter 2 includes a key to help you determine which chapter you should read to learn more about a specimen you have collected. Chapter 2 also includes cautionary statements concerning protected species and protected areas where collecting is not allowed without specific permits. While reading these and other chapters, you may come across terms unfamiliar to you because of their scientific nature. To help alleviate some of these problems, we have provided a glossary at the end of this book. Part II (Chapters 3 and 4) is designed to inform the reader about the basic ecology and biology of aquatic invertebrates in general. This information will help in understanding the general importance of these creatures in the larger aquatic ecosystem, as well as where best to look for them, what their requirements for life are, and how they are used as ecological indicators. Finally, in Part III (Chapters 5-27) you can learn more about the diversity, distribution, form and function (including life history), ecology, and behavior of specific groups of invertebrates as well as how and where to collect them and techniques for culturing these organisms. These chapters also include photographs of specific taxa to help you identify the organisms you have collected. Keep in mind, however, that it is beyond the scope of this guide to identify all aquatic invertebrates to species level. The purpose of this guide is to allow the nonspecialist to identify aquatic invertebrates to an introductory level.

B. Who Needs This Book?

Anyone who is curious about the animals that live in the creeks, rivers, ponds, lakes, and wetlands of North America will benefit from this book, although it is designed for the nonspecialist. Anglers may find this text particularly useful in identifying the critters that local fish are eating, both to use as bait or, for the fly fishing enthusiast, to identify models for wet flies. Many an angler has caught a fish and opened its stomach to see exactly which bugs the fish were hunting at that time of day.

Students in elementary, high school, and college classes may find this text useful for introductory natural history, entomology, zoology, or ecology lectures, field trips, and class projects involving aquatic ecosystems. Similarly, homeschool families can use this text as part of their curricula. Anyone wanting to learn more details about aquatic invertebrate ecology and biology as well as how to further identify aquatic invertebrates in general are encouraged to consult the most recent edition of Ecology and Classification of North American Freshwater Invertebrates (edited by Thorp and Covich in 2010) – the parent text of this guide. For help identifying aquatic insects in particular to much lower taxonomic levels (genus or species), you may wish to consult An Introduction to the Aquatic Insects of North America, edited by Merritt, Cummins, and Berg (2008).

C. What is an Invertebrate?

All living organisms are divided among five groups called kingdoms. These five kingdoms encompass the many species of bacteria (Monera), protozoa (Protista), fungus (Fungi), plants (Plantae), and animals (Animalia). In a very broad sense, animals are divided into two convenient groups: vertebrates and invertebrates. Only members of the former have backbones. Vertebrates are the fish, amphibians, reptiles, birds, and mammals. All other animals are invertebrates; in fact, about 90% of the identified species of organisms on this planet are invertebrates. Some examples of the latter are worms, leeches, snails, clams, insects, spiders, mites, crustaceans, sponges, and moss animals.

D. What Organisms are Covered in This Book?

This guide is designed to assist the user in identifying those freshwater aquatic invertebrates that can generally be seen in moderate detail with the naked eye, or at most with a hand lens. This book covers aquatic macroinvertebrates and not microinvertebrates. The former are typically defined as invertebrates larger than 2 mm long, while microinvertebrates are of course smaller. Microinvertebrates include animals such as most nematode worms, many flatworms, wheel animals (rotifers), gastrotrichs, and protozoans. All these organisms can only properly be identified using a microscope.

Macroinvertebrates can be identified only into broad categories when using this book alone. Even though some of these animals are very large, the body parts that are needed for species level identification can often only be seen through a microscope and require dissection or special preparation. Moreover, proper identification typically requires a great deal of training and/or many more resources. Again, anyone wanting to identify aquatic invertebrates further than the scope of this guide should consult the most recent edition of Thorp and Covich's Ecology and Classification of North American Freshwater Invertebrates, published by Academic Press (Elsevier).

This field guide is primarily concerned with those creatures living on or below the water surface. However, some insects live in aquatic habitats as larvae or nymphs but migrate to terrestrial habitats as adults. These include dragonflies, mayflies, and some beetles and flies. Only the aquatic stages of those animals are extensively treated here. Similarly, the guide generally does not cover those macroinvertebrates living at the shore line but not in the water proper, such as tiger beetles and many spiders.


All organisms are placed into an internationally recognized system of classification in order to establish their relationships to each other. The classification system is hierarchical. This means that all the animals are divided into large groups, and then each large group is divided into smaller groups. Those smaller groups are further divided, until each specific kind is in its own category. This hierarchy is as follows, from largest to smallest:

Kingdom Phylum Class Order Family Genus Species

Each of these categories can be further subdivided if needed into "sub" and "super" categories, as in a suborder or a superfamily, but not all categories need this level of specification for all groups. Each category is called a taxon (plural: taxa), which means "name" in Latin. All the categories (taxa) except species are inclusive categories. This means that these taxa are composed of other smaller groups that share similar bodies or body parts. Only the species level category is exclusive.

All invertebrates are in the kingdom Animalia, which contains around 35 phyla (singular: phylum). Each phylum is defined by having a different body plan. For example, all animals with backbones are in the phylum Chordata. All other animal phyla contain invertebrates. Another example is the phylum Arthropoda, which is defined by having a body with a hard exoskeleton and jointed appendages.

To illustrate how organisms are placed into scientific groups, let us pick an organism, such as the common signal crayfish, to see how one generally classifies a species (see Chapter 2 for details on how to use taxonomic keys). This member of the phylum Arthropoda is native to the northwestern USA and adjacent Canada; but because of its popularity as a food item, it has been widely introduced across the northern and western parts of the continent.

The phylum Arthropoda is divided into several living subphyla: the Hexapoda (insects and springtails), Crustacea (crustaceans), Chelicerata (spiders, mites), and Myriapoda (millipedes, centipedes). Our crayfish belongs to the subphylum Crustacea, because it possesses two pair of antennae. The other subphyla possess either no antennae or at most one pair.

There are five classes in the subphylum Crustacea: Branchiopoda, Cephalocarida, Remipedia, Maxillopoda, and Malacostraca. The branchiopodans have leaf-like legs, so obviously our crayfish with its large claws and stout legs would not fit there. Cephalocarids and remipedes are only found in oceans and have more than 10 pairs of legs, unlike our crayfish. The maxillopodans do not have a telson, which is the central most piece in our crayfish's tail. Thus, our crayfish belongs to the class Malacostraca, whose members have large paired eyes and a strong abdomen with a telson.

The Malacostraca contains several orders. Six of these orders occur in our freshwaters. In the Cumacea, Isopoda, Tanaidacea, and Amphipoda, either the carapace (body shell) is absent or it does not cover the last part of the thorax. Members of the Mysida have seven leg pairs. Only in the order Decapoda, a carapace is present that covers the entire thorax and the five pairs of legs found in our crayfish. The word "Decapoda" literally means "10 legs."

Decapods are a large and diverse group that includes several infraorders (Caridea, Astacidea, and Brachyura) which occur in North American freshwaters. The Caridea contains the shrimp, separated from crayfish by laterally flattened abdomen. The brachyurans are the true crabs; they have an abdomen similar to that of a crayfish, but theirs is very flat and folded up underneath their body. All crayfish are in the Astacidea, with their straight abdomen that is flattened dorsoventrally (top to bottom).

We have now separated our signal crayfish from all other invertebrates, except other crayfish. Two crayfish families occur in North America: Cambaridae and Astacidae. Our crayfish is an astacid, separated from the cambarids by the males not having hooks on the lower parts of their legs. Cambarid crayfish have these hooks so that the male can hold onto the female during mating. The family Astacidae only has one genus in North America, Pacifastacus. This genus contains four species, but our crayfish can be separated from the others easily, because it has only one pair of spines on the tip of its rostrum (large plate that projects forward between the eyes). The other species have more spines, and some have patches of dense hair on their claws. Our signal crayfish lacks these characters, and so it is the species Pacifastacus leniusculus.

The species name is a binomial (literally, "two names"). It is composed of the genus name (Pacifastacus) and the specific epithet (leniusculus). The name leniusculus by itself is not the species name. Traditionally, the species name is always shown in italics, or if it is written by hand, then it is underlined.


A corollary purpose of this guide is to give the user an appreciation for the ecosystems where aquatic invertebrates are found. Many aquatic ecosystems are fragile, or have portions that are fragile in one way or another. For example, it sometimes takes months to years for a diverse community of diatoms, algae, and protozoans to grow on the upper surface of a rock, where the sunlight can reach them. Many invertebrates, including snails, mayflies, and caddisflies, rely on that aquatic garden for food. If one turns over the rock to look for invertebrates, the rock should be replaced so that the rich garden is still available for grazing invertebrates. If the rock is left upside down, the diatoms and other algae will die because no sunlight can reach them. Anyone investigating aquatic habitats should do so with as little disturbance to the habitat as possible.

Similarly, one should try to collect only what you need for your study and not overharvest the invertebrates. Many invertebrates can be cultured or kept in aquaria for observation and study. When the project is concluded, the living specimens should be returned to the water body from which they came.

As an important corollary to this, one should never release an invertebrate into a habitat other than the one where it was originally collected. This is especially true for snails, clams, mussels, crayfish, shrimp, crabs, and other organisms that do not fly. Many species invade new habitats due to human introductions, potentially causing terrible damage. The New Zealand mud snail has now become established in many parts of the USA and Canada, where it outcompetes native snail species that are important food for fishes. In contrast to native snails, this invasive species is difficult or impossible for our native fish species to digest. As other examples, the Louisiana red crayfish, the signal crayfish, and the northern crayfish were all introduced to California in the 1950s, driving one native crayfish species extinct and limiting another formerly widespread species to a couple of springs that are too cold for the invasive species. The zebra mussel, invading from the Ponto-Caspian region clogs water pipes, and just by the sheer numbers and weight of the accumulated individuals, kills crayfish and native mussels to which they attach. In 2002, the International Union for the Conservation of Nature identified nonnative invasive species as the number one threat to biodiversity worldwide.

We want to encourage people to investigate aquatic habitats and also, if possible, to attempt to recreate a small portion of the habitat under study in an aquarium. To enjoy aquatic organisms in an aquarium, you must ensure that the proper temperature, dissolved oxygen, water chemistry, and substrate are combined and functioning in harmony for the survival of its inmates. This forces the keeper to develop at least a rudimentary knowledge of ecosystem functions and hopefully, by extrapolating the effort required to maintain their aquarium microcosm to the larger rivers and lakes around them, develop a greater appreciation for the environment as a whole.

Chapter Two

General Techniques for Collecting and Identification


A. Collecting Legally

The next two sections provide advice on what to do before you collect any invertebrates. They are meant to protect you—not scare you or dissuade you from exploring aquatic habitats.

Before collecting any organism, make certain that you have legal access to public and private sites because trespassing is punishable by law. The public is barred from some types of public lands, especially watersheds providing sources of municipal drinking water; these are generally protected for public health and safety reasons. It is also typically unlawful to collect in state and province parks, national parks and monuments, and wildlife refuges. However, permits are usually available for these areas. Often, all one needs is permission from the park manager or a ranger, and this is usually free. However, the fines can be large without this formal permission. Many U.S. states require permits before collecting invertebrates. In some states a fishing license is sufficient, whereas other states may require a permit only for selected organisms, such as crayfish or mussels. A fishing license is required to collect most crayfish species and bag limits may apply. Many states and provinces do not require children or K-12 classes to have collecting permits.


Excerpted from Field Guide to Freshwater Invertebrates of North America by James H. Thorp D. Christopher Rogers Copyright © 2011 by Elsevier Inc.. Excerpted by permission of Academic Press. All rights reserved. No part of this excerpt may be reproduced or reprinted without permission in writing from the publisher.
Excerpts are provided by Dial-A-Book Inc. solely for the personal use of visitors to this web site.

Meet the Author

Dr. James H. Thorp has been a Professor in the Department of Ecology and Evolutionary Biology at the University of Kansas (Lawrence, KS, USA) and a Senior Scientist in the Kansas Biological Survey since 2001. Prior to returning to his alma mater, Prof. Thorp was a Distinguished Professor and Dean at Clarkson University, Department Chair and Professor at the University of Louisville, Associate Professor and Director of the Calder Ecology Center of Fordham University, Visiting Associate Professor at Cornell, and Research Ecologist at the University of Georgia’s Savannah River Ecology Laboratory. He received his Baccalaureate from the University of Kansas (KU) and both Masters and Ph.D. degrees from North Carolina State. Those degrees focused on zoology, ecology, and marine biology, with an emphasis on the ecology of freshwater and marine invertebrates. Dr. Thorp is currently on the editorial board of two journals (River Research and Applications and River Systems) and is a former President of the International Society for River Science. He teaches freshwater, marine, and general ecological courses at KU, and his Masters and doctoral graduate students work on various aspects of the ecology of organisms, communities, and ecosystems in rivers, reservoirs, and wetlands. Prof. Thorp’s research interests and background are highly diverse and span the gamut from organismal biology to community, ecosystem, and macrosystem ecology. He works on both fundamental and applied research topics using descriptive, experimental, and modeling approaches in the field and lab. While his research emphasizes aquatic invertebrates, he also studies fish ecology, especially as related to food webs. He has published more than one hundred refereed journal articles, books, and chapters, including three single-volume editions of Ecology and Classification of North American Freshwater Invertebrates (edited by J.H. Thorp and A.P. Covich) and the first volume (Ecology and General Biology) in the current fourth edition.

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