Are reptiles really cold-blooded? What does that mean???

We all know that saying, “he’s as cold blooded as a damn reptile!” (or snake or croc), but what does it actually mean?

Does the blood that flows through a reptilian system actually have a lower temperature than a mammalian system? If so, why??? Is this why reptiles generally live in warmer/hot climates?

Also, what significance does this have for a reptile in general? Does it really indicate that they are far “cooler” or less prone to nervous outbursts as humans are? Do they get nervous in the same way that mammals do? Like when I approach a cat, it appears to be really nervous, as well as on it’s guard for me (as a potential predator). However, a lizard appears (or at least gives me the impression that it is) far more sedate than the cat is, even though it is still on it’s guard. Is this because of a natural difference in reptilian and mammalian nervous systems, or is it just a false generalisation?

Also, why are reptiles such efficient predators? Are they truly more mechanical and machine-like than us mammals? Whenever I read about snakes and lizards, they’re target-to-kill ratio appears far better than in the average mammal. Why is this, or how wrong am I?

“Cold blooded” refers to their inability to maintain the temperature of their body without external heat sources. In other words, you put a mammal in a cold environment and it will maintain it’s body temperature close to normal since it can generate heat internally. A reptile can’t and it’s body temperature usually drops with that of its environment. Some reptiles I believe can regulate their temperature a little… but not like the mammals.

IIRC from my Bio 101 class, “cold-blooded” is a bit of a misnomer. A reptile is actually ectothermic, which means that it gets its body heat from an outside source. Mammals are endothermic, which means they generate their own body heat.

I’m sure that if I’m wrong someone will come along and correct me.

Reptiles are just as jumpy and nervous as mammals when faced with danger - they just demonstrate it in a different way. Some reptiles will puff themselves up as big as they can, some will whip out some funky neck flaps that are brightly colored and wave them like crazy (I had an anole that did this), some will freeze and try to “disappear”, some will run away screaming like little girls.

Regarding hunting (this is wild-ass speculation here, FYI), the typical prey of the average reptile is easier to catch (maybe). They seem to hunt things that are smaller and slower than them, as opposed to say a lion trying to take down a wildebeast.

How DO we mammals maintain our body heat, btw?

The Staff Report: What makes some animals cold-blooded and others warm-blooded?, by me and SD Staff Doug, answers some of the questions in the OP.

SD Staff George
Straight Dope Science Advisory Board

Reptiles love heat and seek it out. Herpetologists use special heat pads underneath vivariums to keep their creatures warm. People have a misconception that snakes are “cold and slimy”. They’re always dry (unless they’ve been bathing to slough their skin, or they’re sea snakes) and in my experience, usually warm as they choose to bask in the warmest place.

Let them out of their vivarium, and they will seek to expose as much of their body area as possible to something nice and warm - eg coiling round your wrist, or wrapping themselves round your neck.

Nerves: in my experience, this varies greatly from creature to creature, even within the same species and specific brood/hatching. You might hatch two male brother snakes, and one is always nervier than the other - more snappy, harder to feed, more jumpy - no matter how you bring them up. I found this fascinating, because it was like the snake’s personality. It made them different and unique from one another in another way than just their skin markings.

The fact that reptiles spend much time very still/inert does not relate to how nervous they are. Generally, the more you handle a reptile, the tamer/less nervy it gets, but wild-caught specimens are more than a handful.

In answer to the question about if reptiles have a larger target-kill ratio, I think that it is related to the differences in hunting style necessitated by the differences in metabolism. Mammals regulate their body temperature internally through shivering, sweating, and less extreme methods. Reptiles depend on external power sources, which can allow them to go vast periods of time between feedings. However, this is made up by the fact that this time is spent basking, and they cannot be as active as mammals.

Because of these limitations, reptiles tend to use camouflage and lie in wait until prey comes near enough for a short sprint to catch them. If food does not come by immediately they are equipped to wait for the appropriate time to strike.

Contrast this with the hunting style of a mammal; while they superficially use the ambush technique as well, if they chose mammals can always be on the prowl. If a mammal is hungry it can hunt in the burning sunlight, the cool night, a snowstorm; they can roam large distances in search of food, giving chase quickly and for prolonged periods. This advantage over the reptilian method comes with a price as like the reptilian advantages; a hunting mammal uses far more energy than a reptile and must eat much more often. Fortunately, the advantages and disadvantages tend to balance out.

Being cold blooded has one major implication. Cold blooded animals need to eat far less than warm blooded animals do. I saw a show once that claimed a 12:1 ratio but to me that seems incredibly vague since mammals and reptiles both vary widely in their calorie intake requirements (e.g. a hummingbird proportionately eats more than an elephant [hummingbirds eat more than their body weight daily]).

Of course the downside to being cold blooded is a much more restricted climatic range in which they can live than warm blooded animals can manage. There are instances of reptiles living in colder climates but warm-blooded animals generally have them beat in this case.

As to activity an cold-blooded animal gets more lethargic the colder they are. My cousin (who I rarely see) is a hyper-outdoorsy type living out west. He once related a story to me of a morning hike where he noticed (too late) that he was surrounded by rattlesnakes. They had come out of their winter nests and he said there were tens or hundreds around him (he didn’t wait to bother counting). Luckily, it was still fairly cool and the snakes were exceedingly dull in their reactions and he simply walked out with no trouble. A little while longer, as the snakes warmed up and he might have been in some real trouble.

Of course, predatory ability is all over the place with reptiles as it is with mammale. Mother nature has all sorts of niches where a predator found a successful method of hunting. Ambush/chase, poison/overt strength and so on. I don’t think reptiles are better or worse at being hunters…they simply succeed in their niches. Just don’t think a crocodile is sedentary and slow (they can outrun a dog [and therefore you] in a short sprint).

Reptiles move more slowly when they are cold. They cannot compete easily with mammals that are warm and active while they are cool.

You’re kidding right? The thought scares me.

How is it that cold-blooded reptiles (which cannot generate thier own internal body heat) can move faster than warm-blooded mammals? I ask because shouldn’t thier slower metabolism mean that the chemical reactions necessary for them to produce the energy to move are inhibited/slowed down? Or am I clutching the wrong end of the stick here?

Cold-blooded animals are capable of very rapid bursts of energy, but they cannot maintain high levels like mammals can. For example, a crocodle can attack VERY VERY quickly, latching onto their prey and overwhelming them with that brief burst of speed. But they cannot maintain it. Ever see a crocodile go into a “death roll” when they have prey? That’s an attempt to bring down the prey as quickly as possible. After a couple of minutes, the croc can’t keep it up, and he/she will just stop, and wait until their bodies have regenerated enough energy to continue.

I should be able to explain this in more biochemical detail, but I’m afraid I haven’t studied this material yet for my exam in two weeks :slight_smile:

This all fits in nicely with all the shots on The Crocodile Hunter, with the crocs waiting underwater, and then shooting out very fast, but only about half their body length out of the water. Most animals aren’t paying enough attention, and aren’t fast enough to back up like Steve is. Notice that the crocs don’t pursue him all the way out of the water. I think they’ve been evolutionarlily conditioned to just wait until the next ambush opportunity.

Be afraid. Be very afraid. Well, OK, not really: galloping crocodiles are usually doing so because they’re afraid.

Nope…they can be quite fast. This is how many people get in trouble with crocodiles/alligators. They figure staying 30 feet away with a seemingly slow crocodile makes them safe. It doesn’t. The crocodile can cover that distance very, very quickly. Given it’s very fast reaction and that you have to run backwards to escape (or take time to turn around) the crocodile has a good shot of catching you before you get a step or two especially if you aren’t paying attention and don’t react immediately.

That said I saw a thing on Animal Planet that showed a Komodo Dragon chasing (IIRC) a deer. The dragon was hauling ass and shockingly fast. The deer could outrun the dragon in the long run but this was somewhat more than a 2 second sprint…the damn lizard was chasing down the deer! All the dragon needs to do is get in one bite and then stay near the bitten animal as it slowly dies over the course of a few days.

As mnemosyne said crocs simply can’t keep it up for very long. If they don’t catch you in the first few seconds and you’re still running they will probably give up and stop. You see stuff like this all over the animal world…even with warm blooded animals (although they more than likely can maintain speed much longer than a crocodile). IIRC a cheetah has to catch its prey within a mile of running (maybe a minute or two at top speed). After that it literally overheats and MUST stop (its bodty simply can’t stand anymore). Other animals are built for long distance. Pound for pound a cat can outrun a dog in the sprint but a dog can run much longer. Wolves can follow/chase prey long distances and wear the prey out.

All different strategies each with its good and bad points.

This page has some explanation:

Wolves actually have a great system. They space themselves. So when one chases a deer. By the time the wolf is worn down the next wolf is spaced to take over.

:confused: But if Fido is chasing a deer at 15 mph, his relief, Rover has to do 15 mph to keep up with them.

Wolves hunt cooperatively. It also appears that the “churn” the herd and watch the reaction of its members for animals that seem to be weaker than average. And then by sheer persistance, they keep after that particular animal until they either bring it down or, if they guessed wrong, don’t.

Coyotes are generally solitary but will hunt in small groups. I once say two coyotes slowly approaching some snow geese near a small lake. When they got too close the geese took off away from them and suddenly from out of tulles on the lakeshore another coyote leaped up trying to grab one as the geese passed over. He missed that time but the ruse probably works. I wish he had caught one because it would have been interesting to see whether the prize was shared. Me guess he would have hit the groung running away from his fellow hunters.

quote:"… Well, OK, not really: galloping crocodiles are usually doing so because they’re afraid…"

Great galloping crocodiles Daddy Warbucks!