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Amazing Arachnids

Amazing Arachnids

by Jillian Cowles

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Overview

A richly illustrated and up-close look at the secret lives of spiders and other arachnids

The American Southwest is home to an extraordinary diversity of arachnids, from spitting spiders that squirt silk over their prey to scorpions that court one another with kissing and dancing. Amazing Arachnids presents these enigmatic creatures as you have never seen them before. Featuring a wealth of color photos of more than 300 different kinds of arachnids from eleven taxonomic orders—both rare and common species—this stunningly illustrated book reveals the secret lives of arachnids in breathtaking detail, including never-before-seen images of their underground behavior.

Amazing Arachnids covers all aspects of arachnid biology, such as anatomy, sociality, mimicry, camouflage, and venoms. You will meet bolas spiders that lure their victims with fake moth pheromones, fishing spiders that woo their mates with silk-wrapped gifts, chivalrous cellar spiders, tiny mites, and massive tarantulas, as well as many others. Along the way, you will learn why arachnids are living fossils in some respects and nimble opportunists in others, and how natural selection has perfected their sensory structures, defense mechanisms, reproductive strategies, and hunting methods.

  • Covers more than 300 different kinds of arachnids, including ones new to science
  • Features more than 750 stunning color photos
  • Describes every aspect of arachnid biology, from physiology to biogeography
  • Illustrates courtship and mating, birth, maternal care, hunting, and defense
  • Includes first-ever photos of the underground lives of schizomids and vinegaroons
  • Provides the first organized guide to macroscopic mites, including photos of living mites for easy reference


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Product Details

ISBN-13: 9780691176581
Publisher: Princeton University Press
Publication date: 06/12/2018
Pages: 328
Sales rank: 1,121,448
Product dimensions: 8.10(w) x 10.10(h) x 1.30(d)

About the Author

Jillian Cowles is a clinical microbiologist, naturalist, and photographer. Her photographs have appeared in numerous books and publications, including The Bees in Your Backyard and Bugs Rule! (both Princeton), as well as museum displays, art exhibits, and murals.

Read an Excerpt

CHAPTER 1

Introducing the Arachnids

If "alien" means strange, arachnids are arguably among the most alien of Earth's inhabitants. The archetypal arachnid possesses eight legs, eight beady, unblinking eyes, fangs or pincers, and venom. In addition, the hardened exoskeleton and the multi-jointed legs convey an almost mechanical quality to this living creature; arachnids seem to have stepped right out of the movie War of the Worlds and scuttled into our living rooms. Finally, most are small, fast, and nocturnal, and are therefore difficult to observe. Consequently, the human imagination fills in the gaps in our knowledge, creating fearsome creatures. Ironically, the arachnids that exist in the real world rival anything that our imaginations could conjure. As a group they are many things: tough, resourceful, beautiful, and incredibly diverse — but hardly terrifying. Getting to know these small neighbors who share our planet is immensely rewarding and never dull.

First of all, arachnids are arthropods. Arthropods are characterized by segmented bodies, jointed appendages, and an exoskeleton. This exoskeleton, or cuticle, is composed of layers of waxes, proteins, and chitin. Chitin, which is composed of a derivative of glucose (N-acetylglucosamine), is combined with other substances that enhance its function as protective armor. In many terrestrial arthropods such as insects and arachnids, the chitin is embedded in a proteinaceous matrix of sclerotin. Sclerotin imparts the brown color to many arthropods; as proteins become cross-linked in the sclerotin, it becomes tougher, harder, and darker in a process called tanning. Immediately after molting, arthropods are pale and their cuticle is soft. Over a period of hours or days, as the sclerotin proteins become cross-linked, the cuticle darkens and hardens. In other arthropods such as crustaceans, calcium carbonate is combined with the chitin in a process of biomineralization. This gives the crustacean the perfect armor, combining hardness and resiliency. The major drawback of an exoskeleton is that the arthropod must molt in order to grow in size. Molting is a risky business; the arthropod is susceptible to predation during this time, and sometimes the process of molting itself can lead to injury or death. Despite this, arthropods have been extraordinarily successful from an evolutionary perspective.

Arthropods make up more than 80 percent of all known species of animals, with more than a million described species and millions more yet to be described. Included in this group are hexapods (six-legged arthropods such as insects and springtails), crustaceans (such as crabs, lobsters, shrimp, and pillbugs), myriapods (centipedes and millipedes), and the chelicerata (including horseshoe crabs, arachnids, and sea spiders).

Arachnids have two main body sections (also known as tagmata) and six pairs of basic appendages. The front of the body is called the prosoma or the cephalothorax; it includes both the head and the thorax fused together. The back of the body is the opisthosoma or the abdomen; it contains most of the reproductive and food storage capacity. In some arachnids (such as spiders) these body divisions are clearly evident, but in others (such as mites and harvestmen) the two body divisions merge together without a clear line of demarcation.

Most arachnids have six pairs of appendages at maturity. First and foremost are the appendages that give the subphylum Chelicerata its name: the chelicerae. The most common form of chelicera is a pair of claws consisting of a fixed upper finger and a movable lower finger. Because the arachnid has a pair of chelicerae, it therefore has two of these "hands," each with its own complement of fingers. This undoubtedly is extremely valuable during the manipulation and mastication of prey. Having two hands is certainly far more effective than having only one hand, especially when attempting to cut up food. Many arachnids have some version of these clawlike chelicerae. Exceptions include some mites that have evolved specialized chelicerae for piercing and sucking and spiders that have a single fang as part of each chelicera instead of the two clawlike fingers. In addition, spider chelicerae are even more specialized, being used like hypodermic needles to inject venom into prey. Some species of pseudoscorpions have a special structure on each pincerlike chelicera called a galea. The galea is a spinneret, delivering silk used for building nests. Male mites of some species may also possess specialized structures on the movable finger of their chelicera used for transferring sperm. This may be a fingerlike projection (the spermadactyl), or an opening that receives the spermatophore (the spermatotreme).

The next pair of appendages are the pedipalps. Pedipalps are basically modified legs, and arachnids have evolved an array of variations depending on how the pedipalps are used. In wind spiders (Solifugae), the pedipalps are elongated and resemble long legs; however, they are used primarily in a sensory capacity. In addition, the solifuge palp has a special suctorial organ at the tip of each palp, which assists it in grasping prey as well as in climbing. Other pedipalps resemble claws or pincers. Scorpions, pseudoscorpions, amblypygids, and vinegaroons have robust pedipalps that are utilized in a variety of ways. Scorpions not only use their palps to grasp prey, but the male scorpion also uses his palps to hold the claws of the female while performing his courtship dance. Some species of pseudoscorpions have venom glands in their palps; therefore, they can simultaneously grasp and envenomate their prey. Vinegaroons use their lobsterlike claws for prey capture as well as for digging. The vinegaroon must have an efficient way to carry out the soil that it has loosened as it digs its burrow; the palps function like the bucket of a bulldozer. Harvestmen (Opiliones) have a wide range of different palps. Protolophus shows extreme sexual dimorphism in the size and structure of its palps. The males have large palps that can be used to wrestle a female prior to mating, whereas the females have small palps, each with two delicate fingers. Harvestmen such as Sclerobunus and tiny Sitalcina have raptorial palps with which to grasp prey. Each palp is armed with a row of spines; hence their family name Phalangodidae reflects the palp's resemblance to the line of soldiers holding long spears (the phalanx) used during Alexander the Great's campaigns. Mites have a variety of palps that may be modified for prey capture in predaceous mites, hold-fast structures in parasitic mites, or food filters in microbivorous species. The hollow specialized setae (eupathidium) on the tips of the palps of spider mites (Tetranychidae) have evolved to deliver silk instead of functioning primarily as sensory structures. The majority of arachnid palps are also armed with an array of specialized sensory hairs for the detection of water, food, disturbances in air currents, and temperature measurements. Finally, spiders present one of the most extreme examples of sexual dimorphism and specialized structure in their palps. The female has simple, leglike palps, while the male has complicated palps used for transferring sperm to the female.

The next four pairs of appendages are the legs. In wind spiders, vinegaroons, amblypygids, schizomids, palpigrades, and many mites, the first pair of legs is functionally sensory rather than being used for locomotion. In harvestmen, the second pair of legs serves in this capacity. These sensory legs may be referred to as antenniform legs, especially the extremely elongated and delicate first pair of legs found in the amblypygids and the vinegaroons. Specialized setae on sensory legs detect chemical traces or air movement. The sensory legs of arachnids are held out in front as they walk, tapping the ground at frequent intervals in order to "taste" or feel the substrate in search of food, water, or mates. Hard ticks (Ixodida) have a specialized sensory structure on the tarsus ("foot") of the first pair of legs referred to as Haller's organ. This organ detects chemicals, heat, and humidity, assisting the tick in finding a host. As the tick waits on vegetation, it stretches out its front legs, "questing" for a host from which it will take a blood meal. Many arachnid tarsi are endowed with specialized hairs or structures that enable them to cling to vertical surfaces. In many spiders, brushlike scopula hairs serve this function, whereas pseudoscorpions have a little pad called the arolium between the two claws on each tarsus that allows them to walk on vertical surfaces or the underside of an object. This is an extremely useful adaptation, since pseudoscorpions frequently live and hunt on the underside of rocks.

Perception of the environment is dependent on and limited by the kinds of sensory structures present. An arachnid's cuticle is analogous in function to our ears, nose, taste buds, and temperature receptors. For many arachnids, the cuticle is as important as eyes are to humans. Long, delicate trichobothrial hairs are "touch-at-a-distance" receptors, sensitive to any air disturbance as well as low-frequency vibrations (sound), alerting an arachnid to the presence of predator or prey. A spider can capture a buzzing fly even if its eyes are completely covered. Slit sensilla on the legs may also be used for detecting and locating potential prey. These narrow slits in the cuticle are covered by a thin, easily deformed membrane. Substrate vibrations deform the slit and trigger a nerve impulse, allowing the arachnid to locate moving prey. A single spider may have more than 3,000 slit sensilla, most of which are located on its legs. Although different slit sensilla serve in different capacities, it is thought that some slit sensilla may also function as the "ears" of some arachnids. It is only logical that there is some receptor for spiders to "hear" the stridulation produced by a potential mate during courtship. Specialized hairs of many kinds cover the typical arachnid, including tactile hairs that detect touch and contact chemoreceptive ("taste") hairs that have an open pore at the tip for detecting molecules. Other structures in the cuticle may also be used in olfaction, such as tarsal (foot) organs consisting of small pits that may function primarily as hygroreceptors, detecting changes in humidity. Some structures may be specific to a certain group of arachnids. Only scorpions have the comb-shaped pectines, used for mechanoreception as well as for detecting chemical traces, and only the solifuges have malleoli (racquet organs) used for chemoreception.

For many arachnids, the eyes are of secondary importance compared to cuticular sensory structures. Despite this fact, many arachnids do have eyes, and these eyes can play a significant role in their ability to function. Arachnids have two types of eyes: the main (or median) ocelli and the secondary ocelli. The first type of eyes, the median ocelli, are seen as a pair of eyes on top of the cephalothorax in many orders of arachnids, including the scorpions, vinegaroons, amblypygids, harvestmen, and solifuges. Spiders also have main ocelli, the anterior median eyes, which in jumping spiders form detailed images and may be able to detect colors as well as ultraviolet light. The secondary ocelli correspond to the lateral ocelli in many arachnids. These were compound eyes in ancestral scorpions, as is still seen in their cousin the horseshoe crab. These compound eyes evolved into the simple ocelli that are found in modern scorpions. In some groups such as scorpions, there may be up to five lateral ocelli on each side of the cephalothorax. In many arachnids such as wolf spiders, the secondary ocellus has a tapetum which enhances sight in dim light and is responsible for the "eye-shine" of reflected light from these eyes.

Arachnid eyes are covered by a thin, transparent layer of cuticle that protects their eyes against damage and desiccation. Consequently, arachnids do not have eyelids and therefore cannot blink. Instead, jumping spiders clean their eyes with a quick brush using their fuzzy pedipalps to wipe off any dust. Because the front of the eye is covered with this layer of rigid cuticular exoskeleton, the front of the eye must remain stationary. However, in jumping spiders, the back of the anterior median eye can move. These eyes are roughly conical in shape, and the narrow base of the cone rests in a harness of muscles that can move it. Consequently, the area of the retina (at the base of the eye) can be shifted, aiming the vision of the jumping spider. Of course, the range of movement of the retina is somewhat limited, so the jumping spider orients its cephalothorax in order to better see any disturbance that the smaller eyes had detected.

Instead of forming high-resolution images as jumping spider eyes do, scorpion eyes are specialized for detecting very low levels of light. They even have pigment granules within their eyes that help shield their highly sensitive retinas during the day, comparable in function to sunglasses.

Many arachnids have other light-sensitive structures, although some of these are not fully understood at this time. Some of these are found in unexpected areas of the body, such as the metasoma (tail) of the scorpion, or the tarsi (feet) of snake mites.

The central nervous system (analogous to our brain and spinal cord) processes all the incoming sensory input and controls the response of the animal. In general, arachnids have two major components to their central nervous system: a supraesophageal ganglion or nerve mass (the brain) and a subesophageal ganglion or mass. The brain controls and receives input from the eyes, while the subesophageal ganglion or nerve mass controls the legs and pedipalps while receiving signals from cuticular sensory structures. In the case of scorpions, additional ganglia control other body regions. The cheliceral ganglion wraps around the digestive tube between the supraesophageal nerve mass and the subesophageal nerve mass. It controls the chelicerae. Seven other ganglia are located down the length of the scorpion's body: three in the mesosoma and four in the metasoma (tail). These are all connected by nerve cords and control the opisthosoma, including the action of the aculeus (stinger). Adult spiders have only two major ganglia: the supraesophageal and subesophageal ganglia. The supraesophageal ganglion consists of the "brain" in addition to the cheliceral ganglia. Together, these control the eyes as well as the chelicerae, pharynx, and venom glands. The subesophageal ganglion receives cuticular sensory input and controls motor neurons to the legs and extremities. However, the embryonic development of the spider reveals that this compact arrangement exists only after individual ganglia migrate into the prosoma from the abdomen during development and fuse together to form the impressive subesophageal ganglion. Most other arachnids have some variation of this arrangement. Harvestmen have a large neural mass that consists of two major sections. The protocerebrum together with the deutocerebrum controls the eyes and the chelicerae, while the subesophageal ganglion controls the palps, legs, and opisthosoma. In solifuges, the dorsal cerebral ganglion controls the eyes and chelicera, while the subesophageal ganglion controls the palps, walking legs, and the structures associated with the opisthosoma. Vinegaroons, tailless whipscorpions, schizomids, palpigrades, and mites share this arrangement with slight variations. Pseudoscorpions have a single cerebral ganglion surrounding the esophagus. It is remarkable that these relatively simple arachnid central nervous systems can handle complex tasks involving learning and memory.

Together, the respiratory system and the circulatory system deliver oxygen to the various organs and also remove carbon dioxide, a waste product of respiration. There are three possible respiratory systems found in arachnids: book lungs, tracheae, and cuticular respiration.

The most conspicuous of these are the book lungs, appearing as paired whitish areas just under the cuticle on the ventral surface of the abdomen. The number of book lungs varies with the type of arachnid. Scorpions have four pairs of book lungs while vinegaroons, amblypygids, and mygalomorphs have two pairs. Schizomids and many modern spiders have only one pair of book lungs. Each book lung consists of alternating layers of lamellae and air. The thin parallel layers are stacked such that they resemble the pages of a bound book, giving book lungs their name. Contained within the lamellae is the hemolymph (blood), which picks up oxygen and releases carbon dioxide while passing through the book lung. Because the cuticle of the lamellae is extremely thin, gas exchange can readily occur by diffusion as the hemolymph flows through these hollow, flattened structures. The many stacked layers maximize the available surface area needed for gas exchange. The book lung works somewhat like a bellows, powered by the pumping of the heart. As blood pressure increases during systole, the lamellae fill with hemolymph and the air spaces become compressed. These open up again during diastole, when blood pressure decreases. A small slit opening to the outside allows fresh air to enter the spaces between the lamellae. Although this slit can be opened or closed by muscular control, respiration in arachnids is considered passive compared with ours.

(Continues…)



Excerpted from "Amazing Arachnids"
by .
Copyright © 2018 Jillian Cowles.
Excerpted by permission of PRINCETON UNIVERSITY 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.

Table of Contents

Preface 7

Prologue 9

1 Introducing the Arachnids 10

2 Scorpions: 30

Scorpiones

3 Pseudoscorpions: 52

Pseudoscorpiones

4 Vinegaroons: 68

Thelyphonida (Uropygi)

5 Short-Tailed Whipscorpions: 80

Schizomida

6 Tailless Whipscorpions: 88

Amblypygi

7 Microwhipscorpions: 98

Palpigradi

8 Harvestmen: 102

Opiliones

9 Wind Spiders: 114

Solifugae

10 Ticks and Other Mites: 124

Parasitiformes and Acariformes

11 Spiders: 148

Araneae, the Eight-Legged Puzzle

12 Tarantulas, Trapdoor Spiders, and Their Kin: 164

Mygalomorphs

13 Orb Weavers: 184

Araneidae, Tetragnathidae, and Uloboridae

14 Irregular Web Builders: 196

Theridiidae, Nesticidae, Leptonetidae, Diguetidae, Dictynidae, and Pholcidae

15 Crevice Weavers, Ground Weavers and Sheet Web Builders: 220

Sicariidae, Filistatidae, Plectreuridae, Zoropsidae, Titanoecidae, Amaurobiidae, Oecobiidae, Linyphiidae, and Agelenidae

16 Jumping Spiders: 236

Salticidae

17 Lynx Spiders: 260

Oxyopidae

18 Crab Spiders: 266

Thomisidae, Sparassidae, Philodromidae, Selenopidae, and Zoropsidae

19 Sand Spiders and Wolf Spiders: 274

Homalonychidae and Lycosidae

20 Ghosts, Goblins, Pirates, and Other Wandering Hunters: 284

Mimetidae, Corrinidae, Trachelidae, Gnaphosidae, Caponiidae, Dysderidae, Oonopidae, Anyphaenidae, Miturgidae, Eutichuridae, and Liocranidae

21 Fishing Spiders: 296

Pisauridae and Trechaleidae

22 Spitting Spiders: 306

Scytodidae

23 In the Company of Arachnids 314

Acknowledgments 317

References 318

Index of Common and Scientific Names 323

What People are Saying About This

From the Publisher

"This engaging book is beautifully written and illustrated, and should appeal to anyone interested in natural history. I enjoyed reading Amazing Arachnids."—Paula Cushing, Denver Museum of Nature and Science

"Cowles has assembled a fascinating collection of phenomena pertaining to arachnids and presented it with a narrative that is simply a joy to read."—W. David Sissom, West Texas A&M University

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