The habitat of the creature in question is most commonly atop mountains (or in moist areas). Such an idea would mean that the creature wouldn't need a heart or stomach to break down things into blood. It would most likely become sick easily, as the water it drinks could be disease ridden. The wings, legs and especially brain contain small amounts of liver-like tissue that extract oxygen from the water and uses it in much the same way as our bodys.

Is this possible?

Note- I'm new to this question-answer site, so what I'm saying might be absolutely ridiculous, let me know if I'm way off.

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    – user18912
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    $\begingroup$ Regarding your question: Mountains are (last time I checked) not usually considered moist areas, can you explain the connection? Also why would that mean that they don't need hearts or stomachs? Without a heart your insects don't have a way to transport materials(ATP,Proteins,...)through the body.This can be achieved in other ways, but only in really small bodies,small enough for Oxygen ect. to diffuse through the skin.Can you elaborate how you imagined that? Insects can collect Oxygen via small holes in their shell, getting it by splitting water is probably most inefficient.Can you elaborate? $\endgroup$
    – JFBM
    Apr 22, 2016 at 22:32

3 Answers 3


Yes...and no.

We already use water for blood, we just float things around in it - mostly blood cells but things like platelets etc as well.

In order to be used to carry things around the body of the insect then you need to float things in the water, and then eventually you can't really call it water any more.

So yes you could certainly have a much more dilute liquid, however consider things such as what would heal a cut and prevent all the water squirting out? How would the water carry things like oxygen etc which the insect needs to survive?

See this article for another important point:


Insects do have blood -- sort of. It's usually called hemolymph (or haemolymph) and is sharply distinguished from human blood and the blood of most animals that you would be likely to have seen by an absence of red blood cells. In a sense, as you might guess from the name, hemolymph plays a sort of double role, doing the jobs that both blood and the lymphatic system do in humans and other vertebrates.

Hemolymph is mostly water, plus various other odds and ends like amino acids, ions, lipids (fats), carbohydrates, etc., as well as some pigments, but these are rarely very strongly colored. Typical colors for hemolymph itself are greenish or yellowish. There are also some cells, called hemocytes, that float around in the hemolymph, but they are part of an insect's immune system.

So standard insects already use something different from what we would call "blood", but again it's stuff being carried along by water. Their blood though does not carry Oxygen:

In insects, most of the organs that need oxygen are pretty near the air, and ''breathing" is done by taking in oxygen through lots of little openings to the outside. The oxygen gets to where it's needed mainly by diffusion.

This is actually one of the things limiting the size of insects. They have no way to get oxygen to things deep inside their body.

  • $\begingroup$ If an insect were larger (larger than the 'limiting' size), would this be viable. There is a comment saying that it would be inefficient. $\endgroup$
    – user18912
    Apr 22, 2016 at 22:36
  • $\begingroup$ Water does carry dissolved oxygen and food (sugar). However, blood does a better job. I would think that critters with water for blood would be out competed by those with a more efficient mechanism for transporting food & oxygen. $\endgroup$
    – Jim2B
    Apr 23, 2016 at 2:45

Note: this answer assumes your intention isn't to have a normal circulatory system (only with water instead of blood) but rather that the insect takes in water, pumps it through the body, extracts nutrients and oxygen from it on the way and excretes it after one pass.

If your creature ingests water that provides oxygen and/or nutrients to its body, its mouth essentially takes over the function of the heart, so it would still have a heart.

It would also be limited to whatever nutrients can be absorbed directly, without any processing. That's a very risky situation (a dose of rainwater might cause the creature to starve) and likely to put it so far behind the competition it wouldn't last long if there are any other lifeforms in the area.

Blood is a fine-tuned distribution and maintenance system that provides many benefits aside from transporting nutrients. If blood varied in oxygen, mineral and nutrient content like the average water in the environment, our human brains would have never had a chance to evolve.

Likewise, the digestive system allows creatures to process wildly different food sources, whether they are big and tough (teeth and stomach acid), infected (stomach acid again), have their nutrients locked away (intestinal bacteria) or simply lack some vital nutrients (hey, bacteria again).

As mentioned before, by skipping on the extras, your creature pretty much needs to find the exact nutrients it needs floating in the water. So forget pure and idyllic mountains, think smelly sewage outflow of some really health-conscious humans.

  • $\begingroup$ Interesting, thanks for the answer! $\endgroup$
    – user18912
    Apr 22, 2016 at 22:37

Sponges actually do something like this. They have no enclosed circulatory or digestive systems, instead they directly expose every cell to the surrounding medium thanks to their poriferous body structure, filtering oxygen and nutrients directly out of the water.

However, this mechanism is far too inefficient to sustain the higher energy needs of a mobile animal. Also, sponges live underwater; to repeat this with a land-dweller you'd need the creature to basically be drinking constantly in order to supply itself with dissolved oxygen.


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