1.8 General science

Natural sciences

Life and way of living

Educator section

Memorandum

• All have eight legs. Articulated legs and external skeleton are common characteristics.
• Cephalothorax and abdomen.
• The pedipalps may be large and look like feet.
• On the cephalothorax.
• Simple eyes only, some may be smaller than others: eight in all.

Assignment 4:

1. Spiders are killed by the poison and the numbers of flies increase, possibly because there are fewer spiders.

2. It may be a type of bird that lives on insects and spiders. It might eat poisoned caterpillars, or there might not be enough spiders to eat.

3. It is important to maintain the natural balance.

Leaner section

Content

Activity 9: to study a few arachnids [lo 1.3, lo 2.3, 2.4]

The spider

The spider belongs to the group of arachnids or Arachnida . Some arachnids can spin webs, such as the spider, while others, such as ticks and scorpions, do not spin webs.

Can you still remember the characteristics of all arachnids?

They all have ____________________________________________________ legs.

Can you still remember what characteristic the arachnids share with the insects?

____________________________________________________________________

If your teacher has a dead spider or scorpion, look at its build and try to answer the following questions:

Can you distinguish a head, thorax and abdomen as in the case of the

grasshopper? _________________________________________________________

Why does it look as if there are ten legs? ____________________________________

_____________________________________________________________________

To which part of the body are the legs attached? ______________________________

Can you see small and large eyes as in the case of the grasshopper? ______________

Build

The body of the spider consists of only two parts, namely a cephalothorax and an abdomen. There are eight simple eyes on the cephalothorax (the spider does not have compound eyes like other insects), as well as two palps or feelers. The spider has two conspicuously large pedipalps with which it catches its prey.

There are spinnerets at the tip of the abdomen with which the spider builds cobwebs in which to catch prey.

The skin covering (exoskeleton) is leathery and hairy.

Movement

Spiders are particularly agile, particularly those that do not catch their prey in a web, e.g. the large hunting-spider.

Feeding

Spiders are meat eaters (carnivorous) and paralyse their prey with poison that is stored in their pedipalps. The palps handle the prey while it is being eaten. In South Africa, there are only a few spiders that are harmful to people, e.g. the button-spider (black with distinct markings on the underside; the body excluding the legs is approximately the size of a peanut). However, spider bites can become infected as a result of the germs that are found around their mouthparts.

Respiration

The spider has spiracles on the underside of the abdomen that lead to internal book-lungs .

Maintaining a water balance

As in the case of the grasshopper, spiders obtain the little water that they need from their food.