Field Guide to the Spiders of California and the Pacific Coast States

By R. J. Adams, Tim D. Manolis

UNIVERSITY OF CALIFORNIA PRESS

Copyright © 2014 Regents of the University of California
All rights reserved.
ISBN: 978-0-520-27661-1

Contents

Acknowledgments, ix,
INTRODUCTION, 1,
SPIDER FAMILY ACCOUNTS, 27,
Theraphosidae, 28,
Nemesiidae, 33,
Antrodiaetidae, 35,
Euctenizidae, 39,
Ctenizidae, 43,
Dipluridae, 46,
Mecicobothriidae, 47,
Hypochilidae, 49,
Filistatidae, 52,
Segestriidae, 54,
Caponiidae, 56,
Oonopidae, 59,
Dysderidae, 61,
Trogloraptoridae, 63,
Scytodidae, 64,
Sicariidae, 65,
Diguetidae, 68,
Plectreuridae, 70,
Pholcidae, 73,
Leptonetidae, 77,
Telemidae, 79,
Mysmenidae, 81,
Anapidae, 82,
Uloboridae, 83,
Oecobiidae, 85,
Mimetidae, 88,
Nesticidae, 90,
Theridiidae, 93,
Araneidae, 110,
Tetragnathidae, 126,
Pimoidae, 131,
Linyphiidae, 133,
Anyphaenidae, 140,
Miturgidae, 143,
Clubionidae, 145,
Corinnidae, 146,
Liocranidae, 152,
Prodidomidae, 155,
Gnaphosidae, 156,
Salticidae, 167,
Thomisidae, 180,
Philodromidae, 187,
Selenopidae, 191,
Sparassidae, 192,
Homalonychidae, 195,
Zoridae, 197,
Dictynidae, 198,
Cybaeidae, 205,
Hahniidae, 209,
Zodariidae, 214,
Tengellidae, 215,
Pisauridae, 217,
Zoropsidae, 220,
Oxyopidae, 220,
Lycosidae, 223,
Agelenidae, 232,
Amaurobiidae, 237,
Titanoecidae, 241,
Desidae, 243,
Amphinectidae, 244,
Glossary, 247,
Additional Resources, 253,
References, 257,
Index, 287,
PLATES FOLLOW, PAGE 150,

CHAPTER 1

SPIDER FAMILY ACCOUNTS

THERAPHOSIDAE Tarantulas or Baboon Spiders

Pl. 1

IDENTIFICATION: While the family Theraphosidae contains the largest spiders in North America, it also includes several small desert-dwelling species. All tarantulas have urticating hairs on their abdomens and thick claw tufts on each tarsus. Adult males have two-pronged tibial mating spurs on their first legs. The larger species have thick coats of long hairs over an underlying pubescence, giving them a distinctly furry look, while on smaller species, the long hairs are finer and more diffuse, giving these spiders a more velvety appearance.

SIMILAR FAMILIES: Members of the family Theraphosidae are most likely to be mistaken for velveteen tarantulas (Nemesiidae, p. 33). Superficially similar, nemesiids lack claw tufts and urticating hairs, have noticeably longer posterior lateral spinnerets, and have three tarsal claws. Additionally, these two families have a fairly segregated distribution, overlapping only across a narrow band running through Central and Northern California. Some of the larger wolf spiders (Lycosidae, p. 223) could be mistaken for small tarantulas, but they are generally more overtly patterned, with a distinctive eye arrangement. Wolf spiders also run with their long, thin legs splayed out, while tarantulas generally hold their thick legs closer to their bodies, elevating their cephalothoraxes and abdomens higher off the ground.

PACIFIC COAST FAUNA: One genus with 18 currently described species. The only tarantula genus native to North America, Aphonopelma (pl. 1) is in need of a careful and thorough revision. The vast majority of California’s tarantula species were described by Chamberlin and Ivie (1939), Chamberlin (1940), and Smith (1994). Unfortunately, many of these descriptions were based on only one or two specimens and used features susceptible to a fair degree of individual variation. This has led to a great deal of confusion, leaving many individuals unidentifiable, even when the original literature is consulted. When you attempt to identify a tarantula, even characteristics such as color and size that may be potentially helpful must be used cautiously. A freshly molted tarantula will be darker and more intensely colored than the same spider a few months later. While size can also be an informative feature, enough individuals must have been measured that the range of variation is known for that species. Because of these challenges, many different names have been given to spiders that almost certainly represent only a few, widespread species. In his revision of the Aphonopelma of the northern and western Mojave Desert, Prentice (1997) found that all of the area’s previously described large tarantula “species” were actually representatives of the widespread A. iodius.

Tarantulas are common denizens of Southern and Central California’s lowlands and live in a variety of habitats, from coastal scrub and chaparral to open grasslands and deserts. Along the Coast Ranges, they are found north to the Jasper Ridge region of San Mateo County. They also live in the foothills around the south end of San Francisco Bay and north to Mount Diablo in Contra Costa County. In the western foothills of the Sierra Nevada they have been recorded as far north as the Placer–El Dorado County region east of Sacramento. Tarantulas were formerly more common within the Central Valley itself, but a great deal of the appropriate habitat has been lost to development and agriculture. East of the Sierra Nevada, they can be found in the Owens Valley to the south and in patches of Great Basin Desert to the north, including around Susanville in Lassen County (T. Prentice, pers. comm., 2009).

The Pacific coast’s tarantulas can be broken down into several groups, the most speciose of which is the A. eutylenum complex (pl. 1) with twelve currently recognized species. These are large spiders, 25 to 66 mm (.98 to 2.6 in.) in length, and are found both along the coast and in the interior of the state. They are generally brownish in color (which varies in relation to molt) and share similar patterns of metatarsal scopulation and a fall breeding season. From mid-September through mid-November freshly molted adult males are often seen wandering in search of receptive females.

The second group, known as the A. reversum complex, contains three described species of large tarantulas, including A. steindachneri (pl. 1). In this complex, males emerge in mid-July and for the most part have finished mating and died off by early September. When compared with individuals of similar age, sex, and molt, members of the A. reversum complex are generally darker than members of the A. eutylenum complex (W. Icenogle, pers. comm., 2009). Another feature separating these two complexes is the length of the scopulae on metatarsi IV. On A. eutylenum tarantulas, the scopulae cover more than half the length of the fourth metatarsi. On members of the A. reversum complex, the scopulae are distinctly shorter, covering only the distal half (or less) of the tarantula’s metatarsi IV.

Less conspicuous than their larger cousins are three described species of “dwarf” tarantulas: A. joshua, A. mojave (pl. 1), and A. radinum. These comparatively small spiders are mostly black with a faint blue or silvery-gray luster and range from 14.5 to 28 mm (.57 to 1.1 in.) in length. A. joshua is a summer-breeding species, almost entirely endemic to Joshua Tree National Park. The species narrowly overlaps there with the more widespread A. mojave, which lives throughout most of the Mojave Desert, with distinctive eastern and western populations separated by the Death Valley Basin, and has a fall breeding season. The third species, A. radinum, was described by Chamberlin and Ivie (1939) based on a single male from Manhattan Beach, Los Angeles County, California. Unfortunately, no additional specimens have ever been identified, and the veracity of the location data associated with this spider is questionable.

NATURAL HISTORY: Despite their charismatic appearance and broad distribution, there has been only limited research on North America’s Theraphosidae fauna, especially when compared with the region’s other mygalomorph families. Overall, tarantulas are quite sedentary creatures, rarely leaving the immediate vicinity of the burrow except when forced to do so or, in the case of adult males, when looking for mates. During the breeding period, large numbers of adult males are often seen wandering across roads and fields, initiating the commonly used misnomer “tarantula migration.” In actuality, these males are seeking out females, whose burrows are often patchily distributed across the landscape. Radio telemetry studies on A. hentzi, a large species from the midwestern United States, found that male tarantulas will occasionally travel over a half mile in their search for a receptive female (Janowski-Bell and Horner, 1999). The courtship and mating behaviors of only a few species have been studied in detail. However, they demonstrate enough similarity that a general pattern can be described. Behavioral observations strongly suggest that the webbing along the outside rim of a female tarantula’s retreat provides pheromonal information regarding her state of sexual receptiveness and may act as a beacon, attracting potential mates. Once a male finds the burrow of a mature female, he announces his presence by tapping on the ground with his pedipalps and fore legs. The male may also stridulate by raising and lowering his body in a rapid bobbing motion, creating a high-pitched squeaking sound. An interested female will respond with fore leg drumming of her own. After their initial contact, the female rears up toward the male, forcing him to grapple with her and secure her fangs with the tibial spurs on his front legs. In this position, with her body elevated and fangs held apart, mating occurs. Upon completion, the male quickly disentangles himself and retreats from the larger female. Male tarantulas will attempt to mate with multiple females but inevitably die soon after reaching maturity. Females, in contrast, can live for many years, producing numerous broods throughout their lifetimes (life spans of 30-plus years in captivity have been recorded). As they are so long-lived, it’s not surprising that they are also slow to develop, often taking between four and seven years to reach maturity. While they are widespread across the southwestern United States, patterns of reproductive isolation are apparent. When two or more species of Aphonopelma are found in the same area, often either they are significantly different in size, as A. iodius and A. mojave are, or they segregate by breeding season, as A. eutylenum and A. steindachneri do. In places where A. eutylenum and A. steindachneri occur together, they also separate by microhabitat. In this situation, A. eutylenum is most common on the valley floors and lower foothills while A. steindachneri lives in the upper foothills (C. Hamilton, pers. comm., 2011).

A tarantula is an ambush predator, hunting in a territory that barely extends beyond the entrance of its burrow. Its vision is extremely poor, but its ability to detect the vibrations of a potential prey item passing nearby is exceptional. Once it cues onto its quarry, the tarantula lunges forward and, scooping with its fore legs, impales the prey with its outstretched fangs. The tarantula will then consume its kill undisturbed in the recesses of its burrow.

In addition to their predatory prowess, tarantulas have several defensive tools, the most obvious of which are their impressively large fangs. Although the region’s tarantulas are fairly docile, they will rear up and bite when disturbed. While their venom isn’t harmful to humans, their bite can be painful. Just as fangs guard the front of the spider, a patch of urticating hairs on the abdomen protects it from behind. The tarantula creates a mist of these barbed setae by rapidly brushing its hind legs over the back of its abdomen. If these hairs are inhaled by a predator or get into its eyes, they cause an exceptionally painful burning sensation, and on some people, contact with urticating hairs will produce an uncomfortable rash. The predators most closely associated with North America’s Aphonopelma are the tarantula hawk wasps in the genera Pepsis and Hemipepsis (Pompilidae). These are exceptionally large blue-black wasps with bright-orange wings. Adult female wasps seek out tarantulas, paralyze them with venomous stings, and then bury them with attached eggs. Once the larval wasp hatches, it feeds on the immobilized but still-living tarantula until it pupates to become an adult wasp.

Tarantulas are rather sedentary, often spending many years without straying more than a few feet from the entrance of the burrow. While all Aphonopelma are capable of digging their own lairs, displaced individuals will readily take up residence in abandoned burrows or other acceptable cavities. A tarantula burrow is more or less vertical in its major orientation, ranging from 25 cm to 1 m (10 to 39 in.) in depth, and regularly includes horizontal side chambers filled with the accumulated remains of prey and other debris. It usually terminates in a horizontal den, creating an environment of fairly consistent temperature and humidity. During winter months, many of the region’s tarantulas close the entrances to their burrows with thick plugs of soil and silk, only emerging months later in spring. A tarantula will line the outer perimeter and rim of its burrow with a silk collar, and during the daylight hours, it often puts a silk curtain across its entrance. At night, the tarantula opens up the burrow by pressing the curtain against the walls, steadily building up a thick accumulation of silk at the burrow’s opening. Unlike the larger tarantulas, A. mojave and A. joshua regularly build prominent cone-shaped turrets around the entrances to their burrows. The purpose of the turrets is unknown, but they may act as pheromonal beacons in addition to funneling prey toward the burrow entrance.

NEMESIIDAE Pl. 2

Velveteen Tarantulas, Aggressive False Tarantulas

IDENTIFICATION: Several common names have been used to describe North America’s Nemesiidae, but velveteen tarantula is arguably the most descriptive. They are large spiders, 16 to 30 mm (.63 to 1.2 in.) in length, with a distinctive smooth “velvety” pubescence covering their bodies. They have exceptionally long posterior lateral spinnerets and three tarsal claws, lack claw tufts, and range in color from silvery gray to brown with purplish iridescence on their palps and fore legs. They are also more aggressive than other Pacific coast mygalomorphs. When disturbed, they readily raise their front legs and expose their large fangs. If further provoked, they will bite, and while not dangerous to humans, the bite can be painful.

SIMILAR FAMILIES: Superficially similar to California’s “true” tarantulas (Theraphosidae, p. 28), nemesiids lack long hairs, giving them their more velveteen appearance. Theraphosids also have much shorter spinnerets, only two tarsal claws, and claw tufts on each of their tarsi. Helpfully, Theraphosidae and Nemesiidae only overlap in distribution across a narrow portion of Central and Northern California.

PACIFIC COAST FAUNA: One genus with two generally recognized species (although five species are currently described). The taxonomy of this group is complicated. When Bentzien (1976) examined the original specimens of each of the currently described “species,” he determined that four of the five were indistinguishable, meaning that the North American specimens represented at most two, and possibly even a single, morphologically variable species. However, because this work was never published, all five names are still officially considered valid. Raven (1985) argued that all of North America’s velveteen tarantulas belong in the genus Calisoga (pl. 2), but because two species, Brachythele longitarsis and B. anomala, were never formally transferred according to the rules of zoological nomenclature, they are still officially included as members of the otherwise European genus Brachythele. This is discussed in order to explain incongruities both in the literature and on the Internet. For the purposes of this account, two very similar species, Calisoga longitarsis (pl. 2) and C. theveneti, are recognized. Calisoga is almost entirely endemic to Central and Northern California.

(Continues…)Excerpted from Field Guide to the Spiders of California and the Pacific Coast States by R. J. Adams, Tim D. Manolis. Copyright © 2014 Regents of the University of California. Excerpted by permission of UNIVERSITY OF CALIFORNIA PRESS.
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