Spiders – some people love them, some people hate them. Regardless of where you stand on the subject, you'll find these 10 facts about spiders fascinating.
1. Spider bodies consist of two parts, the cephalothorax and the abdomen.
All spiders, from tarantulas to jumping spiders, share this common trait. The simple eyes, fangs, palps, and legs are all found on the anterior body region, called the cephalothorax. The spinnerets reside on the posterior region, called the abdomen. The unsegmented abdomen attaches to the cephalothorax by means of a narrow pedicel, giving the spider the appearance of having a waist.
2. With the exception of one family, all spiders are venomous.
Spiders use venom to subdue their prey. The venom glands reside near the chelicerae, or fangs, and are connected to the fangs by ducts. When a spider bites its prey, muscles around the venom glands contract, pushing venom through the fangs and into the animal. Most spider venom paralyzes the prey. The spider family Uloboridae is the exception to this rule; its members do not possess venom glands.
3. All spiders are predators.
Spiders hunt and capture prey. The majority feed on other insects and other invertebrates, but some of the largest spiders may prey on vertebrates such as birds. The true spiders of the order Araneae comprise the largest group of carnivorous animals on Earth.
4. Spiders can't digest solid foods.
Before a spider can eat its prey, it must turn the meal into a liquid form. The spider exudes digestive enzymes from its sucking stomach onto the victim's body. Once the enzymes break down the tissues of the prey, it sucks up the liquefied remains, along with the digestive enzymes. The meal then passes to the spider's midgut, where nutrient absorption occurs.
5. All spiders produce silk.
Not only can all spiders make silk, but they can do so throughout their life cycles. Spiders use silk for many purposes: to capture prey, to protect their offspring, to assist them as they move, for shelter, and to reproduce (more on that in a moment). Not all spiders use silk the same way.
6. Not all spiders spin webs.
Most people associate spiders with webs, but some spiders don't construct webs at all. Wolf spiders, for example, stalk and overtake their prey, without the aid of a web. Jumping spiders, which have remarkably good eyesight and move quickly, have no need for webs, either. They simply pounce on their prey!
7. Male spiders use modified appendages called pedipalps to mate with females.
Spiders reproduce sexually, but males use an unusual method to transfer their sperm to a mate. The male first prepares a silk bed or web, onto which he deposits sperm. He then draws the sperm into his pedipalps, a pair of appendages near his mouth, and stores the semen in a sperm duct. Once he finds a mate, he inserts his pedipalp into her genital opening and releases his sperm.
8. Males risk being eaten by their female mates.
Females are typically larger than their male counterparts. A hungry female may consume any invertebrate that comes along, including her suitors. Male spiders often use courtship rituals to identify themselves as mates and not meals. Jumping spiders perform elaborate dances from a safe distance and wait for a female's approval before approaching. Male orb weavers (and other web-building species) position themselves on the outer edge of the female's web, and gently pluck a thread to transmit a vibration. They wait for a sign that the female is receptive before venturing closer.
9. Spiders use silk to protect their eggs.
Female spiders deposit their eggs on a bed of silk, which she prepares just after mating. Once she produces the eggs, she covers them with more silk. Egg sacs vary greatly, depending on the type of spider. Cobweb spiders make thick, watertight egg sacs, while cellar spiders use a minimum of silk to encase their eggs. Some spiders produce silk that mimics the texture and color of the substrate on which the eggs are laid, effectively camouflaging the offspring.
10. Spiders don't move by muscle alone.
Spiders rely on a combination of muscle and hemolymph (blood) pressure to move their legs. Some joints in spider legs lack extensor muscles entirely. By contracting muscles in the cephalothorax, a spider can increase the hemolymph pressure in the legs, and effectively extend their legs at these joints. Jumping spiders jump using a sudden increase in hemolymph pressure that snaps the legs out and launches them into the air.
- Encyclopedia of Insects, edited by Vincent H. Resh and Ring T. Carde
- The Handy Bug Answer Book, by Dr. Gilbert Waldbauer
- Encyclopedia of Entomology, by John L. Capinera