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How the Bugs get Soooooo BIG!

On Earth few arthropods reach large sizes. The ability of Hive creatures to regularly exceed the weight of horses and even larger vertebrates has stunned scientists. If the rules of scale for engineering are true how can animals with external skeletons get so big?

Ever since giant insects became a stable of atomic horror movies in the 1950s scientists have been quick to show why arthropods can’t reach the size of a compact car. The reasoning is based on three issues: The cube/square law means that the external skeletons of arthropods would not be able to handle the disproportionately greater loads of vast size increases. Due to inefficient respiratory and circulatory systems large arthropods would be unable to effectively profuse oxygen throughout their internal tissues. Finally in vertebrates the internal skeleton grows with the rest of the body, external skeletons can’t do this. How does The Hive manage to evade biology and physical constraints and achieve the enormous sizes seen? Let us take these arguments one by one and see what strategies the organisms.

A question of strength:
The structure of arthropods basically consists of a number of hollow rigid tubes. The ability of a tube to withstand stress is based on the strength of the material, its thickness and the load and direction of the stress. As an arthropod gets larger the stress increases by the cube of the difference while the strength only increases by the square. If all things remain constant it seems obvious that large arthropods would collapse under their own weight. However, do all things need to remain the same? The answer is, of course, no. There are at several methods that can be used to support greater mass and associated forces. The most obvious method would be to increase the thickness of the tube walls, make the exoskeleton thicker. There are limits to this, since at some point the structure loses so much interior volume that it can no longer serve as a container for the muscles, nerves and liquids the animals needs to live. A second method would be for the modification of the simple tube into a stronger structure. One way to do this would be for the tube to be fluted increasing its strength greatly while still keeping its weight to a minimum. The basic structure can also be reinforced in other ways, just as flying buttresses keep a gothic cathedral from falling. Finally stronger materials can make up the walls of the tubes. Analysis indicates that chitin as it exists on earth is actually extremely strong and only slight stiffening would be needed to support the increased mass of the aliens.

Every beat of a heart:
Insects don’t separate their internal systems like mammals and other higher animals do. Their functions of respiration and oxygen transport are performed by a single system which doesn’t actively pump blood or draw in oxygen, but relies on interactions between individual molecules to disperse oxygen and energy throughout the animal. This is efficient for small systems but fails completely in larger animals. Of course the simple solution is for these animals to have complex and active respiratory and circulatory systems similar to those of mammals, or better yet birds. It is immediately obvious that such systems exist and can effectively perform the functions needed in large active animals.

Change is good:
Many arthropods are required to shed their skins as they age and grow. Each time they do so the new covering requires time to harden and also reduces the size since any internal supports cannot grow to match the new outer shell. However there is a method used by many types of insects that removes this as an issue. Those insects, such as beetles, butterflies, flies and wasps that undergo complete metamorphosis do not progress through a series of instars that are each slightly bigger and more adult than the one before but make the step from a larva to complete adult in a single complex biological operation. This pathway also seems to suit The Hive well.

So there you have it, how the big bugs got well. . . BIG.

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