VII.

Types of Spiders

Spiders belong to the order Araneae. Scientists typically divide the 40,000 species of spiders into three suborders: the Mesothelae, the Mygalomorphae, and the Araneomorphae.

The suborder Mesothelae is a small, primitive group of spiders that have a segmented abdomen resembling that of early fossil spiders. Spiders of this suborder are sometimes called living fossils since they still exhibit primitive traits that no other living spiders share. Only 40 species from this suborder have been identified, and they live in Indonesia and Japan.

The suborder Mygalomorphae contains about 2,000 species, including tarantulas, trap-door spiders, and purse-web spiders. Although these spiders are not segmented, this group still retains some primitive characteristics, including four book lungs and chelicerae in which the biting parts lie parallel to each other and strike forward and down.

About 32,000 species, or almost 90 percent of all spiders, belong to the suborder Araneomorphae. These spiders are characterized by the presence of two book lungs and a tracheal tube breathing system. They have chelicerae with opposing fangs that work together like a pair of pliers. Many araneomorphs are ground hunters. Although these spiders do not use a web to capture prey, they may use silk for other purposes such as for silk cocoons to protect eggs.

The remainder of this section discusses some interesting spiders and their natural history. The spiders highlighted are organized according to their hunting ability. Ground spiders hunt prey from the ground, while web spiders use webs to ensnare prey.

A.

Ground Spiders

A.1.

Tarantula

True tarantulas are a type of wolf spider that belong to the family Lycosidae in the suborder Araneomorphae. But most people use the term tarantula to refer to about 700 species of spiders belonging to the family Theraphosidae in the suborder Mygalomorphae. Sometimes known as American tarantulas, they are found in tropical regions throughout the world, with many species in the southwestern United States. These giants of the spider world can attain a body length of 10 cm (4 in) with a leg span up to 20 cm (8 in), making it possible for some species to overpower small vertebrates (animals with backbones), such as frogs or lizards, for their meal. Their large body and long legs are covered with hairs, and they have powerful chelicerae, giving them a fearsome appearance.

Most tarantulas stay on the ground (often in burrows). As ground hunters, tarantulas are typical sit-and-wait predators—they wait for insects or small vertebrates to come near before they pounce and kill the prey with their strong chelicerae.

Perhaps as a result of their frightening size and appearance, tarantulas have gained a deadly reputation among humans. For the most part, however, tarantulas do not attack unless provoked, and their venom is not harmful to humans, although their strong chelicerae can cause painful wounds. Tarantulas are popular pets, and some become so tame that they can be picked up and handled safely. Although the chance of receiving a bite is small, there is another danger: Many tarantulas brush off their abdominal hairs when they feel threatened. These barbed hairs fly through the air and can penetrate skin and the mucous membranes of the nose, causing a strong burning sensation.

A.2.

Wolf Spider

About 2,000 species of wolf spiders belong to the family Lycosidae in the suborder Araneomorphae. Found throughout the world, these spiders have dull brown or black coloration, stout bodies, and long, thick legs. Some species have hairy bodies. Wolf spiders are ground hunters, but their name inaccurately suggests that they actively hunt their prey just like their wolf namesake. However, like tarantulas, most wolf spiders usually sit in a hidden spot. When prey happens by, they ambush the prey by jumping on it. Wolf spiders are sensitive to vibrations, such as the buzzing wings of insects, as well as to visual signals. For instance, during courtship males drum their legs on the ground or wave their legs and palps in a rhythmic dance in order to catch a female’s attention.

Female wolf spiders are renowned for their brood care. After laying eggs, a female spider carries the cocoon attached to her spinnerets. When the spiderlings hatch, she allows them to ride on her back for about a week. Some larger wolf spiders dig burrows in the soil, which they may line with silk and provide with a door. At night they leave their burrows to hunt for insects.

A.3.

Jumping Spider

The jumping spiders are active hunters. Depending on the species, they can leap up to 25 times their body length when stalking prey. They belong to the family Salticidae, the largest spider family with more than 4,000 species, in the suborder Araneomorphae. Jumping spiders are found mostly in tropical regions throughout the world, although some species live in high elevation regions in the Himalayas.

Jumping spiders are small spiders, seldom growing larger than 2 cm (0.8 in) in length. Most jumping spiders have somber brown or gray coloration, but a few male species are quite colorful, with iridescent scales and spines and tufts of bright hair. The most striking feature of jumping spiders is their eyes. They have two primary eyes on the front of their cephalothorax that provide exceptionally acute vision. For example, at 20 cm (8 in) they not only see sharp images, but also recognize members of their own species. Their six secondary eyes detect motion. Their excellent eyesight makes these spiders reliant on visual cues for courtship and hunting, and as a result they are active mostly during the day. At night they hide in crevices or under bark, often in small silken cells that they weave for themselves.

During courtship, the male jumping spider identifies himself by dancing in front of a female, waving his legs in a pattern specific to that species. Hunting is also guided by visual cues. The spider’s secondary eyes are able to detect a moving insect, which prompts the spider to turn toward the insect and scrutinize it with its primary eyes. This overlapping visual field produced by the primary and secondary eyes enables the spider to accurately calculate the distance to the prey.

Jumping spiders approach their prey like a cat stalks a mouse. When the spider comes within a few centimeters of its prey, it suddenly leaps by pushing off the ground with its hind legs and then grabs the prey with its front legs. Muscle power and the hydraulic action of body fluids fuel the explosive force of the jumping spider’s legs.

B.

Web Spiders

B.1.

House Spider

The common house spider belongs to the funnelweb spiders in the family Agelenidae in the suborder Araneomorphae. House spiders are found throughout Europe and North America. This spider is so named because its horizontal sheet web is often seen in wall corners of houses, but it can also be found in any cool, dark place such as dense vegetation or crevices of logs or rocks. The spider’s web forms a tube, and the narrowed end serves as a retreat where the spider can hide. When an insect walks over the sheet web, the spider immediately rushes out from the funnel, grabs its victim, and delivers a poisonous bite. The spider then carries its prey back to its retreat, where it begins to feed.

Sometimes house spiders leave their webs and can be seen wandering around or trapped in a bathtub. These are usually males who have given up building webs, but are always in search of a female. Male house spiders lack adhesive hairs on their feet and therefore cannot climb on smooth vertical surfaces, such as those found in sinks and bathtubs. Most house spiders are harmless and may actually prove beneficial to humans since they feed on insects that stray indoors.

B.2.

Garden Spider

Garden spiders belong to the family Araneidae, a group of 2,500 different species of spiders that weave orb, or circular, webs. Marked with varying shades of brown, garden spiders have a distinctive white cross on their abdomens, and some people refer to them as cross spiders. They are found throughout the continental United States, Canada, and Mexico. Some species are found in Europe and Hawaii.

Like most orb weavers, a garden spider typically sits upside down in the middle of the orb web, placing its eight feet on the threads radiating out from the center of the web. The feet act as sensors, picking up vibrations when prey enters the web. When an insect becomes stuck in the web’s sticky spiral threads, the spider rushes out to wrap the victim with silk and give it a paralyzing bite. The spider then carries the prey back to the hub of the web to feed on it.