Sunday, April 19, 2015

Did you know that ... spiders are NOT insects ?!

Watching the latest episode of "The Big Bang Theory" (Season 8 Episode 21 The Communication Deterioration), Sheldon mentions that "Spiders are not Insects".
Honestly I didn't know that, but it's true! As Sheldon says (in his song!) spiders "have two body parts and four pairs of legs" while insects have three body parts and three pairs of legs.

From the webpage of the Explorit Science Center of Davis

Biologists classify animals and plants according to characteristics that they have in common.
Organisms that move from place to place of their own accord and that do not manufacture their food from raw materials in their environment are classified as animals.

spider!Organisms that cannot move from place to place of their own accord (but can be moved by forces of nature or by animals) and that can manufacture their own food from raw materials in their environment, are called plants. Within the huge group called animals are many that have no backbones. These are called invertebrates. The invertebrates include mostly small animals. Some live in water and some on land. Some move around by wriggling, some walk, and some fly. One major group or phylum of invertebrates is called the Arthropoda. Biologists include insects and spiders in this group.


Because they have some characteristics that are different from insects.
Amongst the vast numbers of invertebrate animals in the Phylum Arthopoda, more than a million different kinds have bodies with three main parts--head, thorax, and abdomen. The head has eyes, antennae and mouthparts. The thorax has three pairs of legs. The entire body is protected by a tough outer covering called an exoskeleton. Animals that share these characteristics are called insects. The group to which they belong is called the Insecta.

Another, smaller, group of invertebrate animals has only two main body parts. The body consists of a combined head and thorax called the cephalothorax, and the abdomen. The cephalothorax has the eyes, mouthparts (no antennae) and four pairs of legs. Animals that share these characteristics include ticks, mites, scorpions and spiders. The group is called the Arachnida.


So the take-away facts

spiders are arachnida NOT insects.
Insects are insecta  

but 

arachnida and insecta are both arthropoda (a subgroup of the invertebrates)

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