I recently had a conversation with a friend who informed me she was attempting to design hypothetical alien flora and fauna for a high oxygen alien planet.
Phyllis cited a desire to hear about “strange insects from across the globe” and was inspired to cultivate giant-sized insects the size of mastodons that would roam the wide stretches of continents. She felt talking to a scientist might make her creations more believable or realistic.
I attempted to burst her bubble and informed her that even with the high oxygen content known to be present in the Carboniferous period, the giant dragonfly Meganeura was not actually all that tremendous (2.5 foot wingspan, and probably shorter body),
and like the modern stick insect, was likely able to evolve an abnormal size due to its elongate and extended body still providing for a high surface area to volume ratio. Furthermore, I cited what I had learned in Entomology class: an insect breathing apparatus (spiracle system) would be unable to pull in the large amounts of air necessary to aerate a human or mastodon-sized body directly. Also, I rattled off the structurally fragile quality of an exoskeleton when increased in size by orders of magnitude and the high improbability of giant-sized insectoids producing anywhere near as many offspring as their miniscule cousins do. I tried to explain something about the energy resource to mass ratio, and adaptive trade-offs of maternal parenting vs. high reproductive output.
I then cited the curious case of the large man-eating social arachnids found in the Robert A. Heinlein novel Starship Troopers, and popularized by a movie. In the image below, these ten-foot tall arachnids pour out by the thousands from an underground nest onto a desolate landscape. We are led to understand the entire landscape of the planet is in fact as barren and uninviting as it looks. The arachnids are spread from planet to planet by interstellar meteors that somehow spread insect “spores” (not the right term for insects). What’s wrong with this picture?
Giant arachnids aside (perhaps with real pseudo-lungs or reinforced skeletons) I expressed my sudden disbelief that organisms of such size could reproduce at such a rapid rate and create such large numbers of fighting warriors to combat the would-be human space marines depicted in the movie. For the main reason: the planet is absolutely desolate and there appears to be no plant life or any other kind of food material on the lower level of a food-chain needed to support such a massive number of apparent carnivores (with no apparent true mouths).
Even with verdant savannahs where giant elephants roam, hundreds but not thousands of animals can exist together in a herd, and are in fact made of smaller family structures made by an animal with a long gestation period and only one offspring at a time.
At this point I began to question, other than high maternal care and energy needs, what would prevent an elephant from evolving and somehow producing many smaller young with little maternal care. But I did not delve deeply into the idea…
Part 2: later this week…