http://en.wiktionary.org/wiki/bugbug (plural bugs)
- An insect of the order Hemiptera (the "true bugs").
- (colloquial) Any insect, arachnid, or other terrestrial arthropod that is a pest.
Now, a spider would be #2 arachnid.
http://en.wiktionary.org/wiki/arachnidarachnid (plural arachnids)
- Any of the eight-legged creatures, including spiders and scorpions, of the class Arachnida
Which brings us to spider.
http://en.wiktionary.org/wiki/spiderspider (plural spiders)
- Any of various eight-legged, predatory arthropods, of the order Araneae, most of which spin webs to catch prey.
Which brings us to arthropod.
http://en.wiktionary.org/wiki/arthropodarthropod (plural arthropods or arthropodae)
- An invertebrate animal of the phylum Arthropoda, characterized by a chitinous exoskeleton and multiple jointed appendages.
And finally to animal.
http://en.wiktionary.org/wiki/animalanimal (plural animals)
- In scientific usage, a multicellular organism that is usually mobile, whose cells are not encased in a rigid cell wall (distinguishing it from plants and fungi) and which derives energy solely from the consumption of other organisms (distinguishing it from plants).
