Spider Spider Spiders (order Araneae) are air-breathing arthropods that have eight legs and chelicerae with fangs able to inject venom. They are the largest order of arachnids and rank seventh in total species diversity among all other orders of organisms. Spiders are found worldwide on every continent except for Antarctica, and have become established in nearly every habitat with the exceptions of air and sea colonization. , at least 45,700 spider species, and 113 families have been recorded by taxonomists. However, there has been dissension within the scientific community as to how all these families should be classified, as evidenced by
Ticks of domestic animals animal hosts, but their feeding mechanisms are distinctive. All ticks have an incomplete metamorphosis: after hatching from the egg, a series of similar stages (= instars) develops from a six-legged larva, to eight-legged nymph, and then a sexually developed, eight-legged adult. Between each stage is a molt (ecdysis) which enables the developing tick to expand within a new external skeleton. Ticks are grouped in three families of which two have genera of importance to domestic animals, as follows. The family Argasidae contains the important genera "Argas", "Ornithodoros", and "Otobius". These genera are known as soft ticks because their outer body