The biggy biggy spider broke his cage and got out. He opened up a house and pulled the people out! Along came the Army and shot the spider’s snout. Out came the scientists and started to complain, then the biggy biggy spider ate some more again! (Okay that was bad. I’m sorry.)
My youngest has been having nightmares about spiders. (He has nightmares about the jellyfish he saw SpongeBob catching with a butterfly net too, but that is beside the point.) Over the summer we watched some of the old monster movies. My daughter had become convinced that she wanted to see Jaws with some of her friends (boys who have just reached the monster movie age). I was (still am) convinced she can’t handle it yet, so we started with old black and white monster movies.
The ones that my kids liked the most were the giant insects. Them was the hands down favorite with The Black Scorpion and Tarantula coming in above all the others that we finally gave up watching. Needless to say, this is when the dreams started. Yes, it was my fault. I’m a Bad Dad.
So, they have both asked me why there aren’t giant bugs. Well, there are. Depending on how giant you mean. And when you are talking about. Fossil records indicate there were once were giant dragonflies, millipedes, and other things. How big? The dragonfly (not really a dragonfly, but very similar) was about the size of a kite. The millipede things about five feet long. And check out this recent discovery of a Giant Sea Scorpion over 8 feet long!
So why not now? When I took Biology years ago, it was answered quickly and easily in class. Bugs (Insects, whatever. Its like the tomato. Is it a fruit or a veggie? I will delve into this in Bug or Insect? Fruit or Vegetable? soon.) don’t have the same type of respiratory and circulatory systems we are used to (unless you are an Entomologist.) They have an open circulatory system, which is generally less efficient at providing oxygen to the body. They don’t really have a respiratory system like we do, so the oxygen doesn’t get pumped all over the body, it stays close to where ever the insect lets the air into its body using a tracheal system. This is like a tube filled with air that exchanges oxygen, just like our lungs. But the open circulatory system does not carry that oxygen very far, unlike ours which puts it into fast-track tunnels to our toes. So once an insect reaches too large of a size, any part of it’s body that is too far away from a tracheal tube begins to die of oxygen starvation. Hence, they stay small. Here is an article about it at ScienceDaily.com.
Interestingly, the opposite may have been true once upon a time. An article at National Geographic suggests that the dragonflies had to grow large in order to avoid oxygen poisoning in the ancient oxygen-rich atmosphere.
Don’t tell my kids.
I just have to take a moment to complain. For some reason, while researching places to give you links to back up my memories about what I learned in Biology class (and we are talking a quarter of a century ago), everyone seems to think the reasons insects are smaller now was just figured out on the last 7 years or so. I don’t know. Maybe they are just trying new ways to test the hypothesis. Whatever. I am not a historian, and I get my facts wrong, but, please. Really? Just because a news article re-hashes old news doesn’t mean it just happened. Be careful what sources you trust out there people, we all make mistakes.