Amazing Arachnids: Vinegaroons

Adapted from pages 69-74 of Amazing Arachnids:

Armed with heavy, lobsterlike claws at the front end of their bodies and shooting almost pure acetic acid out of their rear ends, vinegaroons seem to have stepped straight out of a science fiction novel. Despite their fantastic abilities, vinegaroons are perhaps the most poorly understood of the large arachnids. This may be the result of their nocturnal habits, dark nonfluorescent coloration, and the fact that they live most of their lives underground. However, the story of these enigmatic creatures is well worth the cost, albeit paid for in sleepless nights. Their story rivals and even surpasses the creations of fiction.

The common name “vinegaroon” is well chosen. The defensive spray of the vinegaroon Mastigoproctus giganteus of the southwestern United States consists primarily of acetic acid (up to 84 percent), water (10 percent), and caprylic acid (5 percent). Acetic acid is, of course, the component that gives vinegar its characteristic odor. Hydrophilic “water-loving” acetic acid in pure form simply beads up on the lipid-containing cuticle of most arthropods. But with the addition of the lipophilic “lipid-loving” caprylic acid, the spray spreads easily and penetrates into the cuticle. The caprylic acid derives its surfactant properties from a chain of 8 carbon atoms in the molecule, as compared with only 2 carbons contained in acetic acid. The acetic acid spray is produced in a pair of pygidial glands in the abdomen of the vinegaroon. Contraction of muscles in the outer layer surrounding the gland discharges the mixture as a spray from a knoblike structure called the pygidium at the base of the “tail” (called the flagellum). By bending the abdomen and rotating the knob, the vinegaroon can direct the spray with considerable accuracy, even if the target is almost directly in front of it.

As added protection, vinegaroons can defend themselves by spraying almost pure acetic acid from the pygidium, located at the base of the flagellum. By rotating the pygidium, the vinegaroon can aim the spray in almost any direction, even almost immediately in front of it. The flagellum assists the vinegaroon in accurately aiming the spray. Photo by Bruce D. Taubert.

Vinegaroons may spray repeatedly (as many as 19 times) before depleting their reserve of defensive chemicals. It takes about a day for them to recharge their reservoir. The spray has proven to serve as a deterrent to the most formidable arthropod foes such as ants. It also repels vertebrate predators such as the fierce little predaceous grasshopper mice. In contact with human skin, it may cause a burning sensation, and of course the eyes of a potential vertebrate predator such as a bird or a grasshopper mouse would be highly vulnerable to the effects of the acid.

The acetic acid is used purely as a defense weapon—not for capturing prey. A hunting vinegaroon employs tools similar to those used by scorpions for  detecting prey. A combination of sensilla (to pick up substrate vibrations) and trichobothria (to detect airborne vibrations) on the uropygid’s legs allow it to narrow down the general location of its quarry. The tiny hairs on the flagellum might also assist in this task. At the same time, the antenniform legs are extended forward, tapping the surface as the uropygid seeks out prey. Chemosensory hairs on the antenniform legs provide chemical clues as to the identity of any objects it encounters. As soon as the vinegaroon has positively identified a potential prey animal, it charges forward, grabbing with its heavy, clawlike palps. If it misses with the first try, it excitedly feels around with the antenniform legs, searching until it has once again located its quarry.

There are 4 free living instar stages before maturation, and since the young uropygid may not molt following a poor year, it may take from 5 to 7 years to reach maturity. Vinegaroons do not molt again once they are mature, and so their normal lifespan in the wild is probably in the range of 6 to 9 years. Eventually, this magnificent predator slows down due to old age, as joints stiffen and lost appendages cannot be regenerated. Perhaps even in the wild, it may actually die of old age, still a formidable predator to the end.

 

Amazing Arachnids
By Jillian Cowles

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

Amazing Arachnids: Jumping Spiders

Adapted from pages 236-247 of Amazing Arachnids:

Jumping spiders have so many pleasing qualities that it would be difficult to decide what is most admirable about these delightful little creatures. Shimmering iridescence and rich, velvety colors equal the beauty of birds and butterflies. Their fearless capture of prey and their acrobatic leaps surprise and astonish us. Their complex courtship song and dance pique our curiosity. But perhaps the most endearing aspect of jumping spiders is their enormous, forward-facing eyes, gazing at us with every appearance of intelligence and inquisitiveness.

These large, forward-facing eyes, called anterior median eyes, are indeed the key characteristic of this diurnal hunter. Jumping spiders locate their prey visually, stalking and pouncing on it like tiny cats. Unlike vertebrate systems in which one pair of eyes handles depth perception, motion detection, and detail resolution, the spider’s 4 pairs of eyes divide these tasks. Collectively, their 8 eyes create a visual system that rivals any other arthropod’s vision.

Habronattus hallani male. This species of
Habronattus is found throughout a large part of the western United States and into Mexico. It is also primarily a ground hunter.

The force of the grip is due to physical adhesion, not to suction cups or electrostatic forces. If two glass slides are overlapped with a thin film of water between them, they are difficult to pull apart because of the capillary force of the water. The scopula hairs of the spider utilize these extremely strong capillary forces. Apparently the water available in the atmosphere and on surfaces provides the necessary thin film for the end feet to grip the surface. This explains why spiders with scopula hairs can walk sure-footedly on vertical surfaces and upside down, even on glass surfaces. In jumping spiders, the tips of the tarsi (feet) have such dense claw tufts of scopula hairs that they appear to have fuzzy “toes.”

Jumping spiders make up the most diverse family of arachnids in the world, with approximately 6,000 species described so far. As one might expect with such diversity, some jumping spiders have evolved behaviors that fill extremely specialized niches. One jumping spider in Africa, Evarcha culicivora, prefers to feed on bloodfilled female mosquitoes, especially mosquitoes of the genus Anopheles, famous for spreading malaria. Another salticid, Phyaces comosus from the bamboo areas of Sri Lanka, specializes in predating the eggs and hatchlings of other jumping spiders. It is so tiny and so closely resembles a bit of dirt or debris that it can sneak into the nest of another jumping spider undetected. Yet another species, Bagheera kiplingi from Central America, has a primarily vegetarian diet—unique in the spider world. It lives in acacia trees that produce little nubbins of protein and fat from their leaf tips, as well as nectar from the base of the leaves. These provide food for the ants that in return guard the tree from caterpillars and other herbivores. The jumping spider steals the nubbins and nectar despite the ant patrols, living almost entirely on this vegetable source of protein.

In conclusion, jumping spiders rival any other group of creatures for their beauty, diversity, and complex behaviors. A combination of natural selection with sexual selection has produced an array of stunningly beautiful and surprisingly intelligent predators. The world is a richer place thanks to these diminutive gems.

Amazing Arachnids
By Jillian Cowles

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

Amazing Arachnids: The Lace-Weaver Spiders

Amazing Arachnids is a new, month-long series from Princeton Nature. Each week, we’ll highlight one of the unique arachnids found in Jillian Cowles’ richly illustrated and up-close look at the secret lives of spiders.

Adapted from page 229 of the text: 

Broad, black chelicerae and a stocky build give members of the family Amaurobiidae a powerful appearance suggestive of bulldogs. The imposing physique of these spiders contrasts with the delicate beauty of their webs, built of woolly cribellate silk. These characteristic webs give this family its name “lace-weaver spiders” or “hacklemesh weavers.” The cribellate silk of the web radiates out from a tunnel retreat, where the spider lies in wait. Insects become tangled in these hackled threads, giving time for the spider to rush out from its hiding place and catch the prey.

Amaurobius has a truly remarkable natural history in regard to its reproduction. In the case of Amaurobius ferox (an introduced species from Europe reportedly found in southern California), the mother spider lays her first clutch of eggs and stays nearby to guard them until the babies hatch. This maternal behavior is consistent with many other species of arachnids and is therefore hardly noteworthy. But then it gets interesting. After the spiderlings emerge from the egg sac, they interact with their mother, and she is induced by this interaction to lay a second clutch of eggs. This time, the eggs are laid before they are mature, and consequently this clutch of eggs serves as food for the spiderlings that hatched from the first clutch. This is referred to as trophic egg laying and is a strategy employed by several other species of animals, including some species of poison dart frogs. The spiderlings that receive this food are heavier and have a higher survival rate than spiderlings deprived of the trophic egg meal.

Callobius arizonicus. Callobius are found in cool areas, such as the mountains of Arizona and the forests of California.

But the mother spider’s sacrifice does not end there. The mother and her offspring interact further, and this time she actually appears to solicit her babies to feed on her. This the babies do, collectively killing and feeding on their mother. This matriphagy appears to be regulated by the life stage of the spiderlings, the reproductive state of the mother, and the behavioral interactions of the mother and her young. The spiderlings derive considerable benefit from this behavior. They are heavier and larger at the time they disperse compared with spiderlings deprived of their mother as food, including groups of spiderlings given an abundance of other prey to eat.

Finally, the matriphagous spiderlings have a longer period of social behavior, compared with the nonmatriphagous spiderlings. The subsocial spiderlings live together through several instar stages on the web of their mother, cooperatively killing prey and sharing it. The maternal web appears to provide a superior platform for the offspring to detect and cooperatively kill prey, as compared with webs that the spiderlings construct themselves. Prey that would be too large for one or two spiderlings to overcome is killed by groups of spiderlings, and that prey is shared even with those that did not take part in that particular kill. The spiderlings appear to use coordinated teamwork to subdue prey that is up to 10 times the size of any individual spiderling. Cooperative prey capture increases predation efficiency and survival of all the spiderlings.

Most of the members of the family Amaurobiidae live in cool, moist habitats, making their webs under debris, in caves, or in the nooks and crannies of trees. California boasts the greatest diversity of these spiders in the United States. In the arid southwestern states, Callobius arizonicus lives principally at higher elevations where it is cooler and moister. Found under rocks and dead wood, several individual Callobius spiders may share a single shelter. Only centimeters may separate their webs, indicating some degree of tolerance between individuals of the same species. Also like Amaurobius, Callobius guards her egg sac, which is produced in the shelter of her refuge. But in the case of Callobius, it is unknown whether the mother spider feeds her young.

 

Amazing Arachnids
By Jillian Cowles

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