Spiders belong to a large group of animals called arthropods. Insects and crustaceans like lobsters, crabs, shrimp and barnacles are also arthropods. The Arthropods is the largest group in the animal kingdom. Spiders are arachnids, not insects. The Arachnid family includes scorpions, mites, ticks and harvestmen. As you know spiders have 8 legs but insects have only 6 legs. They don’t have antennae while insects have a pair of antennae. The world’s biggest spider is the Goliath Bird-Eating Spider.
Spiders are the largest order of arachnids among all the other organisms. They are found on every continent of the world except for Antarctica. They live everywhere but not in the air and and in the sea. There are around 40,000 different species of spiders. They are different from other arthropods in terms of their body segments. They have 2 body segments. The front segment is called the cephalothorax and the back segment is their abdomen. These two segments are joined together by a small, flexible cylinder. It is called pedicel which help the spider to spin silk without moving the cephalothorax.
The spider’s 4 pairs of eyes, mouth fangs, stomach, brain, legs and the glands that produce the poison are on cephalothorax. Most of the spiders use their fangs to inject poison into their prey. Spiders’ stomach can only handle liquid food and they filters to keep solids out. So what they do is, they will suck the liquid tissue of their prey and leave behind the empty husk of the prey. They basically live on soup! They will use their pedipalps that are next to their fangs to hold their prey as they bite it. At the spiders’ abdomens, you can find spinnerets which produce silk. These silk is used to make spider webs. This silk is actually a liquid protein but it hardens when it is drawn out. The silk is very stretchy. It can stretch out much further before breaking or losing shape. Not all spiders build webs from silk to catch their prey. These webs can also be used as a wrappers for eggs, as a safety ropes for nest building and as parachutes by young ones of some spiders.
There are different sizes spider webs. Their shapes and the amount of sticky thread being used are also different too. The orb-web spiders which are found in gardens, fields and forests build spiral wheel shaped webs which are very sticky. The sheet web spiders make horizontal but uneven sheets with tangles of stopping threads. Insects that hit the stopping threads fall onto the sheet or are shaken onto it by the spider. Then the spider will eat the insects that fallen onto the sheet.
Some spiders spin spin funnel webs. These webs are shaped like a funnel. They have a wider opening on top and get narrower as they go downwards. The sneaky spiders will hide at the bottom of this funnel webs while waiting to devour their prey.
Each spider’s legs consist of 7 important parts. Jumping spiders can jump up to 50 times of their own length. Majority of the spiders hunt at night. They don’t just depend on their webs to capture their prey. Most hunting spiders have thick cluster of fine hairs between their 2 small claws which are at the end of the legs. For example, tarantula spiders. This thick cluster of fine hairs help the spiders to climb smooth surfaces such as glass and upside down on ceiling without falling over. Just like a spiderman. The stickiness of the fine hairs is so strong that the spiders could grip using this force and support 170 times their own weight. They will keep at least 4 legs on the surface while walking or running. If you see spiders with legs curl up, it means that they are dead!
Spiders do not have a skeleton inside their bodies like us. But they have a hard outer shells called an exoskeleton that supports and protects their bodies. Examples of other exoskeleton animals are grasshoppers, cockroaches, crabs and lobsters. Since this outer shells are hard, it can’t grow and stretch with the spiders. So young spiders need to shed their exoskeleton as they grow into adult spiders.
Most spiders have 4 pairs of eyes in the top front part of the cephalothorax . Their eyes are beautifully arranged in patterns and the patterns are different from one family to another family of spiders. The front pair are called “little eyes”. These “little eyes” can only detect the direction from which light is coming. The spiders’ “little eyes” are the main eyes for them which can form images and some “little eyes” of spiders can even turn around to locate their prey. The other eyes of the spiders are called compound eyes. They have poor eye sight but they are very sensitive to vibrations.
Spiders have bristles that will respond to touch. They can also detect forces and vibrations through their joints of their limbs. All these senses are important to web-building spiders compared to the spiders who hunt actively which depend more on their eyes to locate their prey. They also don’t balance well. They depend on their eyes to tell them which way is up.
Spiders comes in various sizes. The smallest is patu digua from Columbia. Its body is less than 0.37mm long. The largest and heaviest spider is tarantula. Its body is about 90mm long and it has a leg spans about 250mm. A mother spider can lay up to 3,000 eggs in one or more silk egg sacs. Some mother spiders will die after laying the eggs. Other mother spiders will find different ways to protect the sacs. She will either attach them to their webs, hiding them in nests, carrying them in the mouth or attaching them to the spinnerets and dragging them along wherever they go.
Baby spiders will turn into larval inside the egg and hatch as spiderlings. They will be very small but similar in shape to their parents. Some spiders take care of their spiderlings. For example, wolf spider’s babies will hand on to the rough bristles on their mother’s back for security. Most spiders live for only 1 to 2 years. However some tarantulas can live over 20 years because they have better shelter and food.
90% of jumping spider’s diet comes from plant. some young spiders feed on nectar. Others feed on dead arthropods, web silk and eating up their own shed exoskeletons. Spiders do eat pollen too. In the captivity, some spider species eat bananas, marmalade, milk, egg yolk and even sausages.
Some spiders use the surface of lakes and ponds as “web” to detect vibration made by their prey while struggling on the surfaces of lakes and ponds. Net-casting spiders build only small webs and use it to capture prey. Spiders camouflage well to avoid their predators like birds. Most spiders are coloured and have stripes and blotches in their bodies. A few spiders have powerful venom, large jaws, dangerous hair or warning colours to protect themselves from their predators.
Some of the spiders which spin webs live together in large colonies and they hunt together and share their food.