FREQUENTLY ASKED QUESTIONS ABOUT SPIDERS
How do spiders differ from insects?
While spiders and insects are both arthropods (animals with an
exoskeleton) and have a lot in common, there are some important
differences that separate them. Spiders are actually arachnids,
a group that includes mites, ticks, scorpions and harvestmen, among
others. The most obvious feature that distinguishes arachnids from
insects is the number of legs. Arachnids have eight, while insects
only have six.
Unlike insects, spiders don't have antennae (feelers). The main
part of the spider's body is also different from an insect's - while
an insect has a head, thorax and abdomen, the spider has the head
and thorax fused into one structure called a cephalothorax.
How many kinds of spiders are there?
About 38,000 species of spiders belonging to 3526 genera of 109
families are known to science. Many spider species are not yet known
to science, particularly in the tropics. Some of the most diverse
and abundant spider families include jumping spiders (Family Salticidae,
4889 species), the sheet-web spiders (Family Linyphiidae, 4214 species)
the orb weaving spiders ( Family Araneidae, 2817 species), the comb-footed
spiders (Family Theridiidae, 2199 species), the wolf spiders (Family
Lycosidae, 2261 species), and the crab spiders (Family Thomisidae,
Where can I find spiders?
Spiders are found all over the world in all sorts of habitats
from the sea shore to the dessert - on the ground, under rocks,
on plants, in trees, in caves, on water, in human dwellings. Each
type of spider tends to be found in a habitat to which it has become
What body parts do all spiders have?
A spider's body consists of a cephalothorax with eyes, mouthparts
- a pair of jaws and a pair of pedipalps, and four pairs of jointed
legs; and an abdomen connected to the cephalothorax by a narrow
pedicel. The entire body is encased by a tough protective exoskeleton
and much of the body has sensory hairs growing from the skin.
How many eyes do spiders have?
Most spiders have eight simple eyes. The two main eyes of a spider
each have a simple lens, and a retina which is made up of light
sensitive cells whose surfaces point toward he light as it enters
the eye. These main eyes have a small field of vision with high
resolution. They are especially well developed in jumping spiders.
A spider's secondary eyes also have a lens but the light sensitive
cells of these eyes point away from the light as do the similar
cells in a human eye. The secondary eyes detect shadows and the
difference between light and dark. A few spider families are characterized
by only six eyes.
Do spiders have claws?
Yes. Spiders have claws at the end of each leg. Spiders' legs
are segmented and each leg has 7 segments: a coxa (attached to the
cephalothorax), trochanter, femur, patella, tibia, metatarsus, and
finally a tarsus which may end in two or three small claws. Web-building
spiders typically have three claws on the end of each leg. The middle
claw and a small tuft of hairs help the spider cling on to its web.
Do spiders have blood?
Yes. Spiders have an open, blood circulatory system. This sort
of blood system has a heart, arteries and veins but no capillaries.
The heart is tubular with a single cavity and with valves to maintain
the flow of blood always in the same direction. The spider's blood
is pale blue due to the presence of haemocyanin dissolved in the
lymph. There are some blood cells but they are for wound-healing
and defense against infection. There are no special blood cells
like the human red cells which carry oxygen around the body.
How do spiders breathe?
Spiders have lungs. There are two sorts of lungs neither of which
is like a human lung. Some spiders have book lungs. A book lung
has a stack of soft plates called lamellae. Oxygen in the air passing
between the lamellae diffuses through the tissue into the blood.
Other spiders have tracheae which are breathing tubes held open
by rings of chitin. The tracheae open to the outside and the opening
is called a spiracle. There appears to be no active, muscular breathing
mechanism. Air seems to pass in and out of the book lung or the
tracheae in a passive manner.
What and how do spiders eat?
All spiders are carnivorous. Most of them eat insects but a few
of the larger species are big enough to prey on small vertebrate
animals like mice or small birds. Most spiders' jaws work from side
to side. They have toothed edges used in breaking up the prey during
feeding. Digestion starts before any of the prey (the food) is swallowed.
Some spiders inject digestive enzymes into the prey before they
start breaking it up; others secrete digestive fluids as they are
breaking the food up with their jaws. The partially digested food
is sucked into the spider's alimentary canal (gut).
Do spiders bite?
Yes. Spiders have two small jaws (chelicerae) that end in fangs
below the eyes on head end of the cephalothorax. Venom (poison)
is produced in glands behind the jaws and empties along ducts in
the fangs to paralyze or kill prey. Relatively few spiders bite
people because they are not able to pierce the skin with their fangs.
The majority of those spiders that can bite people have venom that
is harmless to people. Two notable exceptions are the Brown Recluse
spider and the Black Widow spider which are very uncommon in the
How many spiders have poisonous venom that affects humans?
While there are only a few spiders in India that are really dangerous
to humans, there are significant numbers around the world. The black
widow spider found throughout the United States and recluse spiders
have very toxic venom that can be life threatening to humans. Some
wolf spiders in South America, and some running spiders (family
Chiracanthium) worldwide have venom that causes painful symptoms
in humans. Pigeon spiders of West Africa give very painful bites.
Do all poisonous spider bites have the same effect?
No. When dealing with the effect of spider venom on humans there
are two types. Some spider venom is neurotoxic, i.e. it affects
the human nervous system beyond the site of the bite. The black
widow venom is neurotoxic. A principal component of this venom is
a-latrotoxin. A black widow bite causes rigidity , cramp, and paralysis
of the sympathetic systems. Occasionally it causes death. Other
spider venom is necrotic and causes damage to the tissues surrounding
the site of the bite. The brown recluse spiders have necrotic venom.
The damage usually results in skin blisters, ulcers and blackening
of the local tissues.
How do spiders catch their prey?
Spiders capture their prey in usually four methods.
i) Sedentary spiders living in silk-lined burrows leap out to
capture passing insects.
ii) Some, normally active spiders, lie in ambush on plants, tree
bark, on the ground or under stones.
iii) Hunting spiders go in search of their prey.
iv) Many spiders spin webs to entrap their prey.
Do all spiders spin webs?
No. Nonetheless, spiders that do not spin webs do produce silk.
Some spiders living in burrows line the burrows with the silk from
their silk glands. Young spiders ride the wind on long silk threads,
a process called ballooning. Most spiders put their eggs into silk
What is spider silk made of?
Spider silk is a protein that is formed as a liquid in the silk
glands and squeezed out of spinnerets. The liquid thread hardens
as it leaves the spinneret and some types of such thread become
stronger than a steel thread of the same diameter. Most of the silk
threads in a spider web are multiple strands of fine silk lying
alongside each other. Spiders produce several types of silk from
different types of spinning glands. One type of silk formed by all
spiders is the type used for wrapping prey. Another type of silk
is used to make the egg sac, and yet other is a sticky type often
used as part of a web.
What is ballooning?
This is a method by which the spiderlings of some species such
as katipo and nursery web spiders use to colonise new areas. The
spiderling will climb to a point (such as the end of a branch) where
it is exposed to air currents. It will then produce a small quantity
of silk called gossamer. The wind catches the gossamer and carries
it aloft, taking the spiderling with it. If conditions are right,
the spider may not land for hundreds of kilometres, although a journey
of only a few kilometres would be more usual.