Macrocosmos
BY ALPER ÖZKAN (MBG/IV)
d_ozkan@ug.bilkent.edu.tr
Winter is near, and graduate school applications are the order of the season. Midterms have started as well, so I'd better keep this week's column short, lest I'll be crushed under the weight of, well, everything else to be done. It's been a while since I wrote about animals, so this week will be on them - to be precise, this week is on bigger versions of critters we expect to be generally smaller than us. That's not exactly macrocosm, but I suppose it will do.
The epitome of "critters we expect to be generally smaller than us," of course, are insects. Insects breathe through the tracheal system covering their bodies. Much like our lungs, air goes directly inside those hollow tunnels and delivers oxygen. Unlike our lungs, oxygen is not delivered to blood; the tracheal system directly reaches to tissues. This respiratory system puts a limit on the maximum possible size of insects - if the insect is too large, the tracheae will not be able to effectively bring oxygen to the whole body. Thus, most insects today are generally small, the longest ones being around 55cm in length in the case of stick insects (as their name implies, stick insects are very thin).
Of course, it was a whole different story in Carboniferous and Permian, periods immediately preceding the much more famous Triassic and Jurassic. Plants first colonized the land in the earlier periods and 
started releasing oxygen without many animals to consume it. The atmosphere was therefore quickly hyperoxygenated - ideal for giant insects to evolve. Thus, before the the rise of dinosaurs, insects ruled the early Earth alongside their arthropod kin. Cockroach-like forms were common, and even without us humans to pester, they were as successful as they are now. Another star of the ancient world was Arthropleura, a giant relative of centipedes and millipedes; it measured over two meters in length.
Skies were ruled by giant ancestors of dragonflies, up to 70cm in wingspan and likely able to prey on early land-dwelling vertebrates. Speaking of giant dragonflies, I must also note that there's research going on Arizona State University regarding the effects of oxygen availability on insect growth - dragonflies 15 percent larger than their natural size were reported in the hyperoxygenated environment. If you see crow-sized dragonflies swarming around, you now know who to blame. Come to think about it, perhaps I should apply there. I wonder what their deadline is.
Modern life also features a number of giants, mostly in the deep sea where their great weights can easily be supported. Pillbugs we're used to seeing under rocks get their size upgrade in form of the famous giant isopod, over 30cm in size. The lion's mane jellyfish can have a bell over two meters in diameter, with over 35 meters of tentacles trailing along. Bluebottles, relatives of jellyfish with a coral-like colonial organization, likewise are equipped with tentacles up to 20 meters long, coated with potentially fatal venom. Oarfish can be over ten meters in length, their great size and rather unusual appearance has led to myths of them being kings or leaders of fish in Europe.
And that's it for this week - I honestly haven't the time to write more. If you are interested in overly large animals, Wikipedia as always has a list handy. As for me, well, I hope I'll still be alive come next Thursday.