The spider

Introduction

Web and silk

The body

Sex and reproduction

The jaws and poison

Spider enemies

Blood circulation, the lungs and moulting

Literature and acknowledgements

The nerve system, sensory organs and legs

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These pages are also available in one pdf file: The spider.pdf.


Introduction

Palomena prasina, green bug, an insect

Dolomedes, fishing spider, a spider

 

Many people confuse spiders with insects. The easy way to recognize the spider from an insect is that spider has 4 pairs of legs and an insect has 3 pairs.



An other major difference is that insects have compound eyes whereas the spider has singular eyes with lenses.

 


Unlike insects, spiders do not have antennas.

There are also many similarities. Both have an external skeleton (exoskeleton). The hard part of the body is on the outside while mammals have their skeleton (bones) inside the body. The heart is located on their back. Breathing is performed with trachea and / or book lungs. The oxygen transport protein is hemocyanin and not the mammalian transport protein hemoglobin.

In 1758-59 Carolus Linnaeus published the 10th edition of Systema Naturae in which he classified animals. Over the years the biologists improved the systematic study of the Animal Kingdom. According to this study we have single cell animals at the bottom and at the top are humans with very complex cell systems. With the aid of DNA analysis the positioning of each animal has become even more precise than before. It is called a taxonomical classification of the Animal Kingdom.
It consists of several divisions. A division is called phylum.
Phylum Arthropoda consists of animals with exoskeleton (hardened exterior) that have segmented bodies and jointed appendages. The segments are fused to form body parts. The first part is the head, followed by thorax and the hind part is abdomen. There are appendages on these segments, which are specialized to perform specific functions such as walking, jumping, eating and lots of other activities.

Phylum Arthropoda is divided into 5 major classes.

Class

Crustacea

Arachnida

Diplopoda

Chilopoda

Insecta

Examples

Lobsters, crabs

Spiders

Millipedes

Centipedes

Flies, maggots

Body parts

Cephalothorax and abdomen

Cephalothorax and abdomen

Head and body

Head and body

Head, thorax and abdomen

Pair of legs

Many, usually 5 pairs

4 pairs

Many, 2 pairs per segment

Many, 1 pair per segment

3 pairs, 1 on each thoracic segment

Antennae

2 pairs

None

1 pair

1 pair

1 pair

Described number of species

25,000

40.000

5000?

5000?

800.000

Class Arachnida is divided into 11 orders.

1. Araneae

2. Scorpionida

3. Pseudoscorpiones

4. Solfiguae

5. Schizomida

 

Spiders

Scorpions

Pseudo-scorpions

Solifugids

Tartarida

 

6. Amblypygi

7. Palpigradi

8. Ricinulei

9. Acari

10. Opiliones

11. Thelyphonidae

Tailless whipscorpions

Mini whip scorpions

Rinucleids

Mites en ticks

Harvestmen

Whiptailes scorpions

Accordingly the spider is placed in phylum Arthropoda, class (classis) Arachnida, order (ordo) Araneae. This order is further divided into 3 sub-orders.
The Mygalomorphae (the primitive spiders), the Aranaeomorphae (the modern spiders) and the Mesothelae, with one family of spiders the Liphistiidae.

Every spider belongs to a family, which is further divided into genus, followed by species.
The European garden spider belongs to the family Araneidae, the genus Araneus en the species diadematus. As a rule genus and species are printed in italics.

In our world in September 2008 40462 species in 3964 genera spiders are described.
In June 2008 the folowing 58 families with 5400 species of European spiders were described:

Family count Family count Family count
1
Agelenidae
154
21
Idiopidae
2
41
Salticidae
459
2
Amaurobiidae
95
22
Leptonetidae
65
42
Scytodidae
14
3
Anapidae
6
23
Linyphiidae
1550
43
Segestriidae
19
4
Anyphaenidae
8
24
Liocranidae
63
44
Selenopidae
2
5
Araneidae
179
25
Lycosidae
330
45
Sicariidae
5
6
Atypidae
4
26
Mimetidae
11
46
Sparassidae
27
7
Cithaeronidae
2
27
Miturgidae
34
47
Telemidae
2
8
Clubionidae
73
28
Mysmenidae
16
48
Tetragnathidae
48
9
Corinnidae
34
29
Nemesiidae
55
49
Theraphosidae
9
10
Ctenizidae
11
30
Nesticidae
49
50
Theridiidae
295
11
Cybaeidae
15
31
Oecobiidae
49
51
Theridiosomatidae
2
12
Cyrtaucheniidae
4
32
Oonopidae
44
52
Thomisidae
210
13
Dictynidae
96
33
Oxyopidae
14
53
Titanoecidae
19
14
Dysderidae
348
34
Palpimanidae
7
54
Trochanteriidae
2
15
Eresidae
21
35
Philodromidae
106
55
Uloboridae
14
16
Filistatidae
15
36
Pholcidae
97
56
Zodariidae
92
17
Gnaphosidae
514
37
Phyxelididae
2
57
Zoridae
13
18
Hahniidae
42
38
Pimoidae
3
58
Zoropsidae
9
19
Hersilidae
5
39
Pisauridae
17
20
Hexathelidae
4
40
Prodidomidae
15
number of species
5400

One can find spiders in much larger numbers than expected. The naturalist W.S. Bristowe counted in an undisturbed Sussex meadow 2 million spiders an acre. That is roughly 100 spiders per square meter. An average spider of let's say 0.1 gram in weight consumes its own weight per day. After some calculations we can conclude that in the Netherlands with 15 million human habitants, with an area of 36150 square kilometers there are 3615 billion spider habitants than consume 0.36 million ton per day. These spiders could consume all Dutchmen, weighing 1.2 million ton, within four days. Lucky for us that our spiders do not eat us.

Spiders mostly prey on insects. Most insects are useful, although some may be annoying. Therefore, it is difficult to say if a spider is valuable or not. However, spiders do control the insect population to some extent which makes them helpful, at least, in maintaining the right balance in our eco system.

We will have a close look at the near relatives of the spiders in Europe. Around the Mediterranean we can find the scorpion (order Scorpiones). Its body has a large head-breast part (prosoma) and a segmented abdomen (opisthosoma) to which a tail is connected. At the end of the tail there is a stinger. Connected to the prosoma are four pairs of sturdy legs, one pair of feelers and one pair of scissors.

 

A closer look reveals two tiny black eyes, although, some varieties of scorpions have more than one pair of eyes. The sting with poison is mainly used for protection and for killing large prey. The scorpion sting is unpleasant for humans and can result in possible death. A rather unknown scorpion order is the pseudoscorpion (order Pseudoscorpiones). This small creature is a few millimeter long and lives between detritus like leaves, bark, moss, mole- and bird nests. They have relatively long scissors that can be as long as the rest of the body for the males. They do not have tails or stingers. 
Scorpion Pseudoscorpion

Even smaller than the pseudoscorpion are the ticks and the mites.

Mites are found in a great variety of forms in all kinds of habitats like deserts, in water, between rocks, in flour and in carpets, et cetera. A species of mites, commonly known as house dust mites, can be found in our houses and in our beds in huge numbers where they feed on human dander.
Mites can be detected even in human hair sacs and sweat glands. The excretions of these mites are a major cause of asthma and allergy.
An easy to spot mite is the red velvet mite and it can be found in the garden.

 

Ticks are notorious because the Ixodid family of the ticks may cause Lyme disease. Ticks cut a hole into the skin of a mammal and suck its blood. Because their head is complete emerged into the skin they are difficult to remove.

Velvet mite, Trombidium holosericeum

Tick, Ixodes ricinus

Above a tick in the authors skin and below after unsuccesfull removal

Young tick. A few mm large and frantically running around

Tick, full with blood, sucked from its victim


Harvestmen (order Opiliones) are often mistaken for spiders. Unlike spiders, the two parts of the body (cephalothorax and abdomen) of a harvestman are fused together into one part. They also have eight legs, feelers and mouth parts that work like a pair of scissors.
Most species have short legs but some of them may have very long legs.
Opiliones do not have any poison glands. At the top of the body there is one pair of eyes that are pointed sideways.
They have no silk glands or spinners. Harvestmen eat everything (omnivorous). They catch small insects or eat the decays of any dead animal, animal dung, bird droppings, other fecal material, and all kind of plant material and fungi.
The harvestman is mostly nocturnal, being active during night.

Harvestman, Mitopus morio

Harvestman, Phalangium opilio

 Next: The body

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Ed Nieuwenhuys, December 2011
August 30, 2008, March 23 2008, 15 November 2006 , January 2006.10 January 1999