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The size of insects is limited by the system they have for getting oxygen to their bodies... a system of tubes running through them. The weight of these limits how big insects can grow. The larger beetles tend to be rather slow because of this. Back in the carboniferous, when Oxygen levels rose to perhaps as much as 35%, there were much larger insects.... 60cm dragonflies etc, but as the % of oxygen fell, so did the size of the insects
...Ecdysis A spider undergoes moulting Time series photos of a Tibicen Dog Day Cicada moulting in Ohio USA.The relative rigidity of the exoskeleton means that continuous growth of arthropods is not possible. Therefore, growth is periodic and concentrated into a period of time when the exoskeleton is shed, called moulting or ecdysis, which is under the control of a hormone called ecdysone. Moulting is a complex process that is invariably dangerous for the arthropod involved. Before the old exoskeleton is shed, the cuticle separates from the epidermis through a process called apolysis. New cuticle is excreted by the underlying epidermis, and mineral salts are usually withdrawn from the old cuticle for re-use. After the old cuticle is shed, the arthropod typically pumps up its body (for example, by air or water intake) to allow the new cuticle to expand to a larger size: the process of hardening by dehydration of the cuticle then takes place. Newly molted arthropods typically appear pale or white, and darken as the cuticle hardens.....from Wikipedia: http://en.wikipedia.org/wiki/Exoskeleton
...Larva Stage Why does a Manduca larva undergo five molts?Insects have their skeleton on the outside, this is called an exoskeleton. Exoskeletons make growing bigger difficult. Manduca weighs about 1 milligram when is hatched and about 10 grams just before pupation. To grow that much, the insect is doing some pretty amazing things with it's exoskeleton.There is a limit to how much the insect can grow. Because of the growth limits Manduca must shed it's exoskeleton often.The process of shedding the old skin while building a new, bigger one underneath is called, molting.During molting, the insect usually is usually quiescent (doesn't eat) for many hours to allow a new exoskeleton to develop. After molting, the mandibles are hardened and the insect eats the old shed exoskeleton except the very hardened hood capsule. Once the mandibles are hardened, the insect eats the shed exoskeleton except for the very hardened head capsule...http://manduca.entomology.wisc.edu/about/larva.html
Megarachne, a 300 million year old fossil from the Carboniferous of Argentina was described in 1980 at the world's largest spider; it had a body length of 35cm and leg span of 50cm and can be seen in the Sedgewick Museum, Cambridge.
That is interesting Supercrypted, as it really does look like a spider, with all the spidery proportions and hairs and everything - I'm amazed to hear this. Do you know what the basis for this reassignment is? It's not likely to be DNA - I'd be interested to know.
Quote from: blakestyger on 14/05/2008 09:16:42Megarachne, a 300 million year old fossil from the Carboniferous of Argentina was described in 1980 at the world's largest spider; it had a body length of 35cm and leg span of 50cm and can be seen in the Sedgewick Museum, Cambridge. It has been determined more recently that Megarachne was in fact a type of sea scorpion, not a spider. That means that the largest confirmed spider ever is the Goliath Bird-eater or some other tarantula species. There are, however, a couple of questionable reports in the cryptozoological circle that concern giant spiders. I believe there was a report of a spider in the Congo that was the size of a "pygmy" (I guess something like a 4-foot leg-span). There was also another report (I think in Australia) of a dog-sized spider.