2. Insect respiratory system

Our study of insect internal structure and function will start with the respiratory system. The role of animal respiratory systems is to carry oxygen to the body’s cells for oxidative metabolism. In insects, spiracles open to the atmosphere and attach to a network of silvery-white tubes called trachea. Air containing oxygen enters the spiracles, and the oxygen diffuses along the tracheal tubes to the cells. Unlike vertebrate animals, insect blood does not have hemoglobin and does not carry oxygen. Since fine trachea extend to all the body cells, they also serve as a connective tissue that holds the internal tissues together.

Why Aren’t There Giant Insects?

You ever had one of those terrible, terrible dreams and wake up wondering why there aren’t puppy-sized spiders? These days the largest insect on record is the Giant Weta of New Zealand which can grow up to 10 cm long and weigh around 70 grams, about the size of a small bird. But there was a time… when bugs… were very different. 300 million years ago, insects like the Meganeura Dragonfly with a wingspan of 65 cm across used to fill the skies along with other insects like… 8 times bigger than the ones that we have today. So why then, and not now? Well, Jon Harrison, physiologist at Arizona State University knows probably more about this than anybody else. So we asked him. And our first question was about the most common theory regarding insect size. For a long time experts believed that the weight of an insect’s exoskeleton was what prevented it from growing too much larger. However, Dr. Harrison said that there aren’t a lot of facts to back that up [Dr. Harrison] And, so, people have argued that really, that having an exoskeleton is not compatible with, with, um, being large The interesting thing is really, there’s very little data on that Umm, and the data that there is doesn’t really support it Uh, probably the one thing that supports that idea is the fact that, in the sea, we get much larger arthropods than we do get on land and, of course, in the sea they don’t have to support their bodies [Hank] Harrison also pointed out that the proportion of exoskeleton-to-body-size is the same in large insects as it is in small insects So, the exoskeleton idea sounds kinda like a non-starter So, what else you got, Doctor? [Harrison] Another idea that’s been put forward And that’s really been something that we’ve worked on a lot Uhh, is this idea that relates to oxygen delivery So, insects breathe in an entirely different way from, from humans They have a series of holes along the side of their body And then the oxygen comes in, Through these holes and goes, as a gas, In air-filled tubes And these tubes branch, kinda like a branching tree And get very small, down to the range of a micron in size So, really tiny Uh, and can get down close to every cell [Hank] These tiny tubes are called tracheoles and they deadend in the body cavity where Oxygen diffuses into the insect’s cells Dr. Harrison says that this could be a limiting factor for bugs’ growth In large insects, tracheoles would probably have to be really, really long which would make the diffusion of Oxygen difficult But, that might only be a problem given the Oxygen levels we have in the atmosphere today Another theory is that giant insects were possible in the past because there was a lot more Oxygen in the air [Harrison] And that idea has gotten some recent support From geologists who showed that In the late Paleozoic, atmospheric Oxygen rose to well above what it is today, Right now, it’s 21% Oxygen, In the late Paleozoic, we think it was about 32% Oxygen And that happens to coincide with when we had much larger insects than we have today And so that, kind of, has boosted this idea that Oxygen delivery is what keeps insects small And that higher Oxygen in the atmosphere could enable them to get bigger [Hank] In the end, Dr. Harrison says we don’t have definitive answers, only theories But, what ever the reason is, I, for one, am happy with bugs staying the size they are In fact, if we could get them a little smaller, I wouldn’t mind If you have any questions for experts, we are happy to try to find experts to answer them for you So, let us know those questions, or any other ideas or comments you have in the comments below Or on Facebook or Twitter And we’ll see you next time

Roly Polies Came From the Sea to Conquer the Earth | Deep Look

Roly Polies Came From the Sea to Conquer the Earth | Deep Look

Pill bugs…… roly polies….. potato bugs… whatever you want to call them, somehow there’s something less creepy about these guys than other insects. More loveable, or something. Maybe it’s because they’re not insects
at all. Pill bugs are actually crustaceans. They’re more closely related to shrimp and
lobsters than crickets or beetles. Pill bugs even taste like shellfish, if you
cook them right. Some adventurous foragers call them wood shrimp. As early as 300 million years ago, some intrepid
ancestor crawled out of the ocean, sensing there might be more to eat, or less competition,
on dry land.” But unlike lobsters, pillbugs can roll up
into a perfect little ball for protection. If you look closely you can see the evidence
of where these guys came from. Like their ocean-dwelling cousins, pill bugs
still use gills to breathe. True insects — like this cricket — use a
totally different system. See those tiny holes on this cricket’s abdomen? They’re called spiracles. They lead to a series of tubes that bring
fresh air directly to the insect’s cells. But pill bugs don’t have any of that. To survive on land, they had to adapt. Their gills, called pleopods, are modified
to work in air. Folds in the pleopod gills developed into
hollow branched structures, almost like tiny lungs. In a way, the pillbug is only halfway to becoming
a true land animal. Because… they’re still gills. They need to be kept moist in order to work. Which is why you usually find pill bugs in
moist places, like under damp, rotting logs. They can’t venture too far away. Sure, pill bugs look like the most ordinary
of bugs. But they’re much more than that: evidence
that over evolutionary time, species make big, life-changing leaps. And those stories are written on their bodies. Hey, while we’re on the subject of oddball
crustaceans… check out this episode about mantis shrimp. Their eyes see colors we can’t even
comprehend. Their punch is faster than Muhammad Ali’s. And while we have you: Subscribe. OK? Thank you! And see you next time.