c
 

What is a spider?

Life Cycle:

Hatching and Development

Reproduction

Silk and Webs

Prey Capture

Spider Senses

 

What is a spider?

            A spider is a member of the taxonomic kingdom Animalia (animals), the phylum Arthropoda (includes insects, spiders and crustaceans), class Arachnida (arachnid eg. spiders, ticks, scorpions) and order Aranea (spiders).

            Arachnids are different from insects as they only have two main body parts ( the cephalothorax, and the abdomen). All spiders have four pairs of legs and a set of leg-like appendages called palps. Most spiders have eight eyes, although some have six or two. There are even a few species that are found in caves don’t have any eyes at all. Unlike insects that have compound eyes, spiders only have simple eyes and their vision ranges from the excellent eye sight that enables the Salticidae to hunt to near or complete blindness.



Life Cycle of a Spider

            Hatching and Development:

Females lay eggs in an egg sac. Each egg sac contains anywhere from on to thousands of eggs. Some female spiders guard their eggs by either carrying it around with them or creating a protective retreat for it that is easily defendable. Other spiders lay their eggs and create a egg sac and leave their spiderlings to their fate.

Spider eggs normally only take a couple weeks to develop and hatch. The main exception for this is for some spiders in temperate regions where the spiderlings spend winter in the egg stage of development and wait to hatch until spring.

Once the spiderlings hatch they disperse either by walking or by a process called ballooning. Ballooning occurs when a spiderling climbs up to the top of an object (branch, blade of grass etc.) and releases a wisp of silk into the wind. The wind on an updraft picks of the spider and transports it anywhere from a few feet away to hundreds of miles away. Because of this dispersal mechanism spiders are often some of the first creatures to colonize a new habitat or a destroyed.

Spiderlings undergo five of more molts before they reach their adult size and while most spiders no longer molt after reaching maturity, some spiders continue to molt for their entire lives.

            Reproduction:

Male spiders have no external sex organs. Instead they release their sperm into a sperm web and hold it in their palps until they can desposite it into the female’s reproductive opening located on the ventral side of her abdomen. Some males have elaborate mating courtship behaviors used to convince the females that it would be better to mate with them rather than eat them.

Females store the sperm in a spermathecae (a internal sperm holding tank) from which she can fertilize her eggs. Egg fertilization occurs a few weeks later just before the eggs are laid into their egg sac.

            Silk and Webs:

All spiders produce silk that emerges from it’s spinnerets. Most spiders have three pairs of spinnerets and may possess up to six different kinds of silk glands (each making their own kind of silk). Not all spiders however make webs. Those spiders that do make webs tend to have very specific web patterns that can help identify the family of spiders.

Because of the strength, elasticity and lightweight material engineering research has been trying to create spider silk artificially. Some of its potential uses include lightweight bulletproof vests, lightweight parachutes, and lightweight climbing and rescue ropes.

            Prey Capture:

All spiders other than those in the family of Uloboridae have venom that they excrete through hollow fangs. Spiders either bite prey first to kill it and then wrap it in silk for digestion and consumption or they immobilize the prey first with silk and then bite it once it is immobilized.

After the prey is killed and wrapped spiders put enzymes in the bite site to pre-digest the prey until the soft tissues are completely liquefied. These liquefied remains can be ingested by the spider. Spiders have a really interesting digestive pathway, they use their stomach lumen to pump the remains through their body and store food in extensions of their digestive system that is located in almost all parts of their body.  This allows spiders to store large quantities of food which enables them to go long periods of time without eating.


Spider senses:

While most spiders have some sense of sight, many are nocturnal so don’t primarily rely on that sense. Instead the hairs on spiders serve as chemo and mechanical sensors that can respond to touch, vibrations, chemical signals and air currents. 

Open hairs at the ends of the palps and legs serve as taste receptors and can distinguish between different substances upon contact. While spiders do respond to airborne smells at this time we don’t know what organs are involved in this process.