“If you want to live and thrive, let a
spider run alive!” That is an old English saying that means not killing spiders
will bring you good luck. There is also a myth that killing a spider will bring
bad weather.
Letting a spider live won’t bring you good luck or
good weather. But scientists say there is no good reason to kill a spider. Most
spiders will not harm you. They rarely bite. Only 30 of the 40,000 species
(kinds) of spiders cause illness when they bite people. The black widow and the
brown recluse are two spiders that have painful or deadly bites.
Spiders are important to the balance of nature. Spiders
eat mosquitoes and other insects. Spiders help keep insects under control.
ARE SPIDERS INSECTS?
Spiders are arachnids. They are not insects. Daddy
longlegs, mites, ticks, and scorpions are also arachnids.
You can tell spiders and insects apart.
Spiders have eight legs. Insects have six legs.
The bodies of spiders have two parts. The head and thorax
(chest) form one part, and the abdomen is the second part. The two parts are
linked by a thin stalk called the pedicel. The bodies of insects, on the other
hand, have three parts. A spider’s body has a hard outer shell.
Insects have antennae, and most of them have four wings.
Spiders do not have any wings or antennae.
HOW BIG ARE SPIDERS?
The biggest spiders are tarantulas. They have
bodies that are more than 4 inches (10 centimeters) long. A tarantula’s legs
spread out over 8 inches (20 centimeters). The smallest spiders have bodies
that are less than 0.04 inch (1 millimeter) long.
HOW DO SPIDERS MAKE WEBS?
Spiders spin webs out of silk threads. The silk
comes from glands in the spider’s abdomen.
The glands make a liquid. The liquid goes out
through tubes as thin as a hair. The tubes are called spigots. The spigots go
to spinnerets on the spider’s abdomen. Dozens of spigots go to each spinneret.
The spinnerets are like fingers. They can move to stick silk threads to a wall
or wrap prey (animals they eat) in silk.
WHY DO SPIDERS MAKE WEBS?
House spiders, garden spiders, and other spiders spin
webs to catch prey. Some webs are shaped like funnels. Some webs are flat. Some
webs are like a circle. The spiders feel the web vibrate when a fly or other
insect gets trapped in the web’s sticky threads.
Not all spiders spin webs, but all spiders
make silk threads. Spiders leave a silk thread behind them as they go. They can
use this thread to make a quick escape. Spiders use their silk to make nests.
Some spiders use their silk to wrap up captured
prey. All spiders are carnivorous (meat eaters). They eat insects and
sometimes other spiders.
Scientists divide spiders into two groups called web
spiders and ground spiders. Ground spiders hunt their prey. Wolf spiders and
other ground spiders have long, thick legs. They wait for an insect to come
along and then jump on it.
HOW DO SPIDERS EAT?
A spider has special mouthparts called
chelicerae. There is a sharp fang at the end of each chelicera. The fang is
hollow. The spider stabs its prey with the fang. Poison from a poison gland in
the spider’s body goes through the fang and into the prey. Big tarantulas are
powerful enough to kill frogs and lizards. Small jumping spiders that live in
the tropics can jump a long way to attack prey.
Spiders cannot chew their food. The spider spits
juices into the wound made by its fang. The juices start to digest
(break down) the prey outside the spider’s body. The spider’s stomach has
muscles that are powerful enough to suck in the digested prey.
A spider can use its mouthparts for
things other than eating. It can use them to carry prey. Ground spiders use
their mouthparts to dig tunnels in the soil.
DO SPIDERS HAVE HAIR?
Some spiders have hair on their bodies. All spiders
have hairs on their legs. Spiders use their hairs to feel and smell things.
Each leg has seven parts with joints between them.
The hairs of many tarantulas have barbs like
tiny fishhooks. Tarantulas can brush off their abdominal hairs when they feel
threatened. The barbed hairs fly through the air. They cause a burning feeling
if they get in your skin or up your nose.
HOW DO YOUNG SPIDERS GROW?
The male spider fertilizes eggs from a female
spider. The female makes a silky cocoon for her eggs.
Some spider mothers hide their cocoons and then
leave them. Other spiders guard their cocoons until the eggs hatch. Female wolf
spiders carry their cocoons on their bodies until the eggs hatch.
Spider eggs hatch inside the cocoon. The young
spiders go through different life stages. The first stage is as a white,
wormlike larva. After about two weeks, the larva changes into a spiderling.
Spiderlings look like grown-up spiders, only smaller.
Spiderlings lose their hard outer shell a number of
times as they grow. A new shell takes the place of the old one. This is called
molting. Small spider species may molt about 5 times. Some large tarantulas may
molt as many as 40 times. The last time a spiderling molts it becomes a
grown-up spider.