Why Isn't this a daily occurrence?
Between my time in Chicago and my time in Urbana, I've lived almost 15 years in Illinois, ending in 2008. And I have to say, other than sitting through all of 'The Beginning of the End' (featured above) at the Insect Fear Film Festival that I never ran into a single giant grasshopper.
And I imagine that inquiring minds want to know why not?
Our mythology and our B movies are populated with gigantic monsters that menace both us and our infrastructure. And yet, in our day to day grind we worry about all kinds of things: theocracy, war, corporate takeover, crime, pie, and so on, but we don't generally lose sleep over the idea that a giant cockroach will flatten our house.
For the most part we live in a world where the movers and shakers are small: bacteria, algae, insects, and so on. But why should it be that way? Why doesn't our landscape look like an amalgam of 1950s science fiction? Why are organisms the sizes they are?
This is a big topic (ha ha) and I'll probably spend a few diaries on it. In this one we'll introduce the basics and go back to the movies.
Here's a somewhat better known 1950s classic.
The Blob! is an amorphous mass, basically a giant amoeba. Here is a real amoeba for perspective.
The generic amoebae as depicted here are pretty big given that they are a single cell. They may be around 0.1 mm in diameter, visible as a tiny dot against the appropriate background. Why aren't they attending Bela Lugosi features and snacking on other members of the theater-going public?
There are several answers to this question but the most fundamental, and the one why are going to concentrate on tonight, has to do with the mathematical ratio between the surface area and the volume of an organism (or part of an organism).
For the sake of simplicity lets say that the shapes of an amoeba and The Blob! when at rest are approximately a sphere. An amoeba has a diameter of about 0.1 mm and The Blob! at that point in the film a diameter of about 10 m (or 10,000 mm).
The formulas for the surface area and the volume of a sphere are 4Πr2 and the volume is 4/3Πr3.
Please forgive the crudeness of my formulae .
The amoeba has a surface area of 0.03 mm squared and a volume of 0.0005 mm cubed. The ratio of surface area to volume is 60 (i.e. 60 mm square of surface area for every 1 mm cube of volume).
The Blob! has a surface area of over 314 million mm squared and a volume of over 523 billion mm cubed. Its surface area to volume ratio is 0.0006.
If The Blob! is a gigantic single cell it faces a number of challenges. The surface area:volume ratio has got to be at the top of its list. In most biological situations volume is going to represent demand and surface area is going to represent supply. The amoeba's volume is going to determine how much oxygen and food it needs to sustain itself. It's going to determine how much waste it produces. The surface area of the cell is where the food and oxygen comes in and the waste leaves.
For any given shape, volume increases as a cube of a linear measurement and surface area increases as the square of a linear measurement. This means that as a shape increases in size, the volume increases faster than the surface area.
Which spells big trouble for The Blob!. Because of its huge size it only has a tiny surface area to supply each cubic mm. There's no way it can absorb enough oxygen and get rid of waste rapidly enough. To make matters worse, waste and nutrients don't just have to enter the cell - they have to move through the cell. In a tiny amoeba, they can easily diffuse in no time at all - not so for The Blob!.
Hopefully it is now obvious why all large organisms are multi-cellular. Or, to put it a different way, why cells are always small. Being composed of many small cells gives have a larger surface area as volume increases.
But let's not give up on The Blob! yet. Here is, Physarum a plasmodial slime mold.
Probably the closest thing on earth to The Blob! although on a more relaxed schedule. Still in manages to get big and basically remain a single cell (it has many nuclei but no internal divisions into cells)?
Here's a closeup.
The slime mold is highly branched, giving it a very large surface area for its volume.
A fungus is a more sophisticated variant of the same idea. The bodies of fungi consist of long filaments composed of many cells laid end to end. These filaments are called hyphae and the many hyphae making up the body of a fungus are called a mycelium. The hyphae grow through the environment and absorb nutrients directly from it. A fungus is basically a mass of threads. This body form can allow a fungus to grow indefinitely in size
In contrast the bodies of animals are constrained in size by their need to move. Movement requires a compact body which requires sophisticated organ systems that provide large (internal) surface areas for important biological functions. We will discuss the impact of size on these structures in future diaries. I'll finish by noting that advantages of being large are obvious - fewer things can eat and you can travel father and eat more things. By size has costs in terms of acquiring energy and nutrients, movement, and even supporting yourself.
Let's finish by discussing one example - giant insects. It is no accident that most insects are small. A small insect is light and strong, capable of rapid movement and a wide range of shapes. Large insects run up against the limits of their body's structure.
Insects don't have lungs. They exchange gases with the environment through a series of air passageways called tracheae that permeate their body. Gases can be pumped in and out to a limited extent through abdominal contractions but for the most part gases move through diffusion. Fine is you are tiny - not so great if you are the size of a subway.
The external skeleton of an insect is very strong for its weight at small size. An insect leg is like a straw. When the straw is narrow it is strong, even if the walls are fairly thin. If you increase the diameter of the straw, the walls are likely to buckle, unless you make them so thick that it becomes too heavy.
So the giant grasshopper can't breathe and its skeleton will buckle under the insect's weight.