The Brown Recluse Spider

By Richard S. Vetter

The brown recluse is a fascinating spider very well adapted to dwelling in houses and other buildings. Because of this very quality and the ghastly reputation associated with the medical consequences of its bite, it has become infamous throughout North America. Although recluse spiders can cause serious skin injuries and, in very rare cases, death, the danger posed by this spider is often exaggerated as a result of arachnophobia and the misdiagnosis of non-spider-related conditions as brown recluse bites. These misdiagnoses often occur in areas of North America where the spider does not exist, making legitimate bites improbable. One of the greatest factors that keeps the myths alive is misidentification of common (and harmless) spiders as brown recluses. With this book, Richard S. Vetter hopes to educate readers regarding the biology of the spider and medical aspects of its bites, to reduce the incidence of misdiagnoses, and to quell misplaced anxiety.

In The Brown Recluse Spider, Vetter covers topics such as taxonomy, identification, misidentification, life history characteristics and biology, medical aspects of envenomations, medical conditions misdiagnosed as brown recluse bites, other spider species of medical consideration (several of which have been wrongly implicated as threats to human health), and the psychology behind the entrenched reasons why people believe so deeply in the presence of the spider in the face of strong, contradictory information. Vetter also makes recommendations for control of the spider for households in areas where the spiders are found and describes other species of recluse spiders in North America. Although The Brown Recluse Spider was written for a general audience, it is also a valuable source of information for arachnologists and medical personnel.

• Language: English
• Publisher: Comstock Publishing Associates
• Release date: May 7, 2015
• ISBN: 9780801456152

Book preview

The

BROWN

RECLUSE

SPIDER

RICHARD S. VETTER

CONTENTS

Acknowledgments

Introduction

1 | Taxonomy

2 | Identification

3 | Misidentification

4 | Life History and Biology

5 | Distribution

6 | Medical Aspects

7 | Medical Misdiagnoses

8 | Human Psychology and the Brown Recluse Spider

9 | Bites and Alleged Bites by Other Spiders

10 | Control Measures

Glossary

References and Further Reading

Index

ACKNOWLEDGMENTS

I thank Kitty Liu, Susan Specter, and Peter Potter of Cornell University Press for helping turn my goal of publishing this book into a reality. Two anonymous reviewers made comments on the first draft and Gavin Lewis made many comments on the final draft that greatly improved the end product. Diane Barger reviewed the chapter Life History and Biology and the late Dr. Gary Wasserman of the University of Missouri–Kansas City School of Medicine and the Children’s Mercy Hospital, who reviewed Medical Aspects and Medical Misdiagnoses, each provided valuable comments and suggestions. I acknowledge dear friend Mary Ursula Holden, who, after spending her days at her official profession of book editing, did me the generous favor of using her crepuscular and nocturnal hours to work on this book as well. Much knowledge was gained over the years from my association with the Barger family (Diane, Brenna, Dale, and Bradley) of Lenexa, Kansas, who willingly turned their 1850s-built, brown recluse–populated home into a live-in laboratory where we collaborated on several studies of the species. Appreciation goes out to Rachel Kuypers, who allowed me to use an image of her smiling face after she suffered a mild brown recluse envenomation. I appreciate my association with many medical colleagues over the years who helped me understand the medical aspects of loxoscelism while eagerly absorbing in exchange biological and taxonomic information that I offered regarding brown recluses and other spiders. In particular, I must single out the following dermatologists for their understanding and tutoring: Dr. David Swanson, Dr. W. Van Stoecker, and Dr. Gary Wasserman. I acknowledge the dozens of my arachnological colleagues, many being members of the American Arachnological Society, with whom much recluse information has been exchanged over the last two decades. Finally, I appreciate the scores of pest control personnel, entomologists, and public health officials, and the hundreds of homeowners who submitted spiders for identification, who thereby made possible a better understanding of recluse spider distribution in North America

INTRODUCTION

The brown recluse is a very common house spider in specific parts of the United States and can be found by the hundreds in the proper environment. Originally it was just a small brown creature in which very few people, including arachnologists and medical personnel, took any interest, but it came to national prominence in the United States after 1957, when it was determined to be the source of dramatic skin lesions in humans. During the 1960s, there was a rush to generate information regarding its biology, life history traits, venom composition, and envenomation consequences. Brown recluse bites usually do not lead to severe symptoms, but about 10% of cases develop necrotic (rotting flesh) lesions that may require skin grafting. In very rare conditions in North America (fewer than 1% of cases), a systemic reaction can occur, most often in children, which can be fatal if not diagnosed and remedied quickly. As a result, the brown recluse now induces fear where it is found, and even where it is not found: the brown recluse’s infamous reputation causes people to believe they see this spider in parts of North America where it does not exist. The brown recluse spider is therefore a source of much concern for homeowners, especially those buying or selling houses, and it provides significant revenue for the pest control industry.

Spiders in general share an infamous reputation with bats and snakes, the result of guilt by association with the few members of each group that are actually harmful. In fact, only two main North American spider groups are recognized as truly causing threats to human health: the widows and the recluses. Among the former, the black widow is well researched, its medical effects are well established, and the biological aspects of its life history are well known. However, knowledge of the brown recluse lags behind the wealth of information for the black widow, and as a result, misinformation and misconceptions fill the gaps between popular thought and arachnological knowledge. Although in most cases this merely results in the telling and retelling of harmless myths, the reiteration of these myths can sometimes cause real damage.

One example of this damage occurs when ill-informed physicians diagnose brown recluse spider bites as the cause of skin lesions in areas of the continent where recluse spiders of any species are exceedingly rare or have never been found. When the quantity of brown recluse bite diagnoses greatly outnumbers the verified specimens of recluse spiders in a particular area, it logically follows that the spiders cannot be responsible for all these incidents. Some of these misdiagnosed skin conditions, such as cancer, lymphoma, group A Streptococcus bacterial infection, and Lyme disease, can cause great suffering, irreversible damage, and possibly death. When a wrong diagnosis is made, spider bite treatment is ineffective and the correct treatment is delayed or never given.

A second example of myth overriding fact involves misidentification of harmless spiders as brown recluses. Most of the North American human population living outside indigenous brown recluse spider territory do not have the sufficient skills to accurately identify the spider. Or rather, because these people are unaware of the actual identity of the many spiders that they perceive to look similar to brown recluses, many harmless spiders are misidentified as such. This can lead to unnecessary, inappropriate, and occasionally dangerous abuse of insecticides or other pest control methods, which are more threatening to human health than the spiders.

At the time of writing, there was no widely available work for the general public summarizing the state of knowledge regarding the brown recluse and other recluse spiders in North America. This book attempts to fill this gap. Of course, much of the information provided here is based on the scientific literature, listed in the references under the applicable chapter heading. Other sources include the unpublished knowledge of local authorities who have dealt with the brown recluse spider for decades. Surprisingly, for some aspects such as local distribution within various states, oral history is the best available source of knowledge.

Basic information for the general public is provided here, along with sufficient scientific data to make this book a worthwhile contribution to the field of arachnology. Some readers may skim topics they already know and others may struggle through more difficult material, such as unfamiliar medical aspects. Common names for spider species are used where they exist, but in order to provide scientists with the most accurate research results, the spiders’ scientific names are also given. In this way, the book can be a resource for readers at all levels. It can provide information to the general public about these spiders that so thoroughly grip the American psyche; it can dispel and defuse the mythology surrounding them, replacing hyperbolic hearsay and word of mouth with scientifically accurate information; and it may also spur other arachnologists to study the brown recluse.

Finally, this book describes some of the procedures occurring behind museum walls and university doors, and thereby gives readers both a historical and a behind-the-scenes view of how science works in a particular field, how it has advanced to the present state of knowledge, and perhaps also where it is going. Often the task of describing species may appear very dry and boring but it also involves the most fascinating detective work, which the scientist pursues in awareness of the steps (and missteps) of the people who contributed early on and helped define the field for the future. It is like looking into a stream and realizing how much water has flowed past but also how much more will flow for decades to come. It gives the scientist a feeling for his or her place in time and in the field.

1 | TAXONOMY

It is best to start by describing where the brown recluse fits into the grand scientific scheme of things—its classification as a species, which will serve as a reference point. The biological classification system can seem confusing or even overwhelming with its sometimes long and unfamiliar terminology, but it is really just a series of steps that move downward from one category to a lesser one. The classification scheme for the brown recluse spider, then, is as follows:

Figure1.png

Spiders are in the kingdom Animalia. They belong to the phylum Arthropoda (creatures with jointed feet or legs), which contains many familiar groupings of animals such as insects, crustaceans, millipedes, and centipedes. Moving further down the categories of classification, spiders are in the class Arachnida. Members of this class have eight legs in adult form and mouthparts called chelicerae (singular: chelicera). (The chelicerae in spiders are the movable mouthparts to which the fangs attach.) Spiders are in the order Araneae; other arachnid orders include, for example, the Scorpiones (scorpions), Acari (mites and ticks), Opiliones (daddy longlegs—but not the daddy longlegs spiders which of course are in the order Araneae), and Uropygida (vinegaroons).

Within the order Araneae there are in turn many subdivisions. There are three infraorders, of which the most primitive is a missing link, the Liphistiomorphae, which are not found in North America but are of great interest to arachnologists studying the evolution of spiders. The remaining two infraorders are the Mygalomorphae and the Araneomorphae. The mygalomorphs are slow-growing spiders with many ancestral features, and include the tarantulas and other closely related species. The araneomorphs are known as the true spiders, but a better name would be the common spiders; in any case, the recluse spiders belong to this group.

Within the araneomorphs, two large divisions are found: haplogynes and entelegynes. Haplogyne means simple female, which describes the relatively primitive structure of the female reproductive organs of this group. In comparison, the entelegynes (meaning complete females) have more complicated reproductive structures. Brown recluse spiders belong to the haplogynes, which causes difficulty in species determination because of the simple structure of their reproductive organs, which does not allow for easily observable variation among species.

Farther down the classification ladder are the genus and species names. which are combined to form the scientific name of any particular organism, also known as the binomial (double name). Usually, the two parts of the binomial are derived from Latin or Greek. For example, the honey bee’s scientific name is Apis mellifera: apis is the Latin word for bee and mellifera means honey-bearing. The species name, or specific epithet, may also give a hint regarding some physical feature of the organism. For example, the specific epithet of the spider Steatoda albomaculata translates as white-spotted, from the markings on this species’ abdomen. The scientific name for the brown recluse spider is Loxosceles reclusa. The genus name, Loxosceles, is pronounced locks-AW-sel-eez, which rhymes somewhat with the well-known isosceles triangle (triangle with equal legs) from geometry class and is formed from two Greek words: Loxos- is from the word for slanted, crooked and -celes is from the word for legs. The name slanted legs comes from the way spiders of this genus hold their legs when at rest (Fig. 1.1). The specific epithet reclusa is an obvious reference to the behavior of these spiders in seeking places to hide, although this is a characteristic of many species of spiders of many genera.

So far as the common name brown recluse spider is concerned, this book conforms to the strict scientific practice of using such a common name to refer only to one species, not to a group of several species—in this case, to Loxosceles reclusa, which is found almost exclusively in the south and central midwestern United States. In North America, several other Loxosceles species have common names; the desert recluse spider found in the deserts of Arizona and southeastern California is named Loxosceles deserta, the Big Bend recluse found in southern Texas is Loxosceles blanda, the Apache recluse is Loxosceles apachea. Many other Loxosceles species found throughout the world do not have common names quite simply because they are not common; many are only known from a handful of specimens and are often found only in the one location where the original specimens were discovered. However, as a genus, the Loxosceles spiders are also known in North America as violin spiders, fiddle back spiders, or recluse spiders. In South America, Loxosceles spiders are referred to simply as brown spiders—a poorly conceived and simplistic common name, because so many spiders of entirely different genera are also brown. In this book, the Loxosceles genus in general is referred to as recluse spiders. However, nonarachnologists frequently refer to any spider of the genus Loxosceles as a brown recluse spider, although this is not technically correct. For most aspects, including the medical, this is mainly a semantic argument, because what pertains to the brown recluse spider medically pertains with minor variations to all recluse spiders. Nevertheless, there are some behavioral and physical differences between the brown recluse spider and various closely related species, so it is important to be careful when using common names.

Fig. 1.1 The genus name of the recluse spiders, Loxosceles, comes from the Greek for “slanted legs” because of the way in which the spider positions itself at rest. This spider is a male Chilean recluse, Loxosceles laeta.

Fig. 1.1. The genus name of the recluse spiders, Loxosceles, comes from the Greek for slanted legs because of the way in which the spider positions itself at rest. This spider is a male Chilean recluse, Loxosceles laeta.

One additional aspect of scientific naming is that sometimes changes occur. This is something that nonscientists may find odd; it would seem that once an animal or plant receives a scientific name or classification grouping, it should stick forever. Unfortunately, this is not the case. Scientists discover more species and determine new evolutionary relationships by spending more effort examining a group of organisms; new technology such as the scanning electron microscope or techniques to determine DNA sequences enables scientists to discover new information about organisms; and sometimes the accumulation of this new knowledge leads to changes in how organisms are lumped together or split apart in the hierarchy of categories. For example, several spider species were dispersed around the world before arachnologists starting naming them. Arachnologists on different continents then gave names to their local spiders, and sometimes the same species was given several scientific names by different people working independently. Decades later when there was better communication worldwide, this or that researcher realized that these specimens from different areas of the world were all the same species, whereupon the oldest specific epithet took priority and the other epithets became obsolete. As a result, a very common scientific name that might have been frequently used in the literature might become no longer valid—as indeed happened in the case of the first recluse spider species named in Europe.

The first recluse spider specimen was named Scytodes rufescens in 1820. The genus name Loxosceles was erected in 1832 for a circum-Mediterranean spider at the time named Loxosceles citigrada. This same species was given several additional names until, in 1873, the youthful French arachnology prodigy Eugène Simon examined the different specimens, decided that they were indeed all the same species, and settled on the name Loxosceles rufescens. (Simon published his first spider taxonomy book, which is still considered to be a classic, when he was only 16 years old.) Not surprisingly, the Europeans were very active in naming Old World animals because the European scientific world was far more developed than that of the Western Hemisphere at the time. As the spider fauna of the New World became better known, sometimes they were given Old World names because the spiders were thought to be the same species. Years later, after more specimens were collected from different areas of the world and greater scrutiny was applied to these, specific epithets were created to describe them. Until then, however, an older, incorrect name was often used for the sake of convenience. For example, the brown recluse spider of North America was long known by the European name Loxosceles rufescens, and did not receive its scientific name until 1940 when American arachnological luminary Willis Gertsch and his colleague Stanley Mulaik designated it Loxosceles reclusus. (Gertsch gave scientific names to all forty-eight species of Loxosceles spiders of Central and North America and the Caribbean Islands.) Several scientific papers published before 1940 use the old, incorrect name, which can lead to confusion among readers who are not aware of the history of the brown recluse’s scientific nomenclature.

Another problem arises from the fact that the Greek and Latin languages from which scientific names are derived assign grammatical gender to all nouns and the adjectives that modify them; thus, the specific epithet (usually an adjective) has to have the same gender as the genus name (usually a noun). Although the recluse spider genus name has never changed, when Gertsch and Mulaik originally named the brown recluse spider, they mistook the genus name Loxosceles as masculine and used the specific epithet reclusus—the masculine form of the adjective. However, Loxosceles is one of many ambiguous Greek words that can be read as either masculine or feminine; it is actually feminine. Later, in 1958, Gertsch realized this mistake