Tall/short vs. high/low
I have 3 questions regarding the usage if these words.

1) Should we use TALL/SHORT when we talk about all the animals, birds, insects, etc., or should we use HIGH/LOW for those animate beings whose horizontal dimensions exceed the vertical ones? E.g., is it correct to say that "a snake is taller than an ant", or that " a crab is shorter than a duckbill"?

2) We say "a tall tree", but "a high fence". Should we say "a tree is higher than a fence", or "a tree is taller than a fence"?

3) When do we say "a tall building", and when is it better to say "a high building"?

Thank you!

PS: It may seem that I´m exaggerating with the examples, as someone will consider them a little bit odd, but that´s exactly what I do with my 2-year daughter when we practice the comparison of the different objects.

Question

Tall/short vs. high/low
I have 3 questions regarding the usage if these words.

1) Should we use TALL/SHORT when we talk about all the animals, birds, insects, etc., or should we use HIGH/LOW for those animate beings whose horizontal dimensions exceed the vertical ones? E.g., is it correct to say that "a snake is taller than an ant", or that " a crab is shorter than a duckbill"?

2) We say "a tall tree", but "a high fence". Should we say "a tree is higher than a fence", or "a tree is taller than a fence"?

3) When do we say "a tall building", and when is it better to say "a high building"?

Thank you!

PS: It may seem that I´m exaggerating with the examples, as someone will consider them a little bit odd, but that´s exactly what I do with my 2-year daughter when we practice the comparison of the different objects.

Answer

General rule:

1. tall/short = height of an object (or 'vertical length' if you prefer)(a linear dimension)

2. high/low = distance from the ground. (a difference in elevation)

Tall buildings have floors that are very high above the ground.

Sometimes it depends on your perspective.

A "high fence" is really a tall fence whose top edge is high above the ground.  While tall fence is more correct, most people only care about how far (high) above the ground the top of the fence is.  If the top of the fence is high above the ground, we often call it a "high fence".

Answer

Ooo, good questions. 
1) Yes, use tall/short for animals, high or low makes me think of relative placing eg "the snake is higher than the ant" I would assume means the snake is on higher ground (or in a tree) than the ant.
2) I have a tall fence at the bottom of my garden but you are right, I would rarely say "a high tree", again, my instinctive reaction to that is that it refers to a relative placing eg it's higher up the mountain than the other tree.
3) I need to think about this one! I'm struggling to think of an example of when I would say "a high building" but it doesn't sound wrong to my ear.

Great questions, really making me think!

Answer

For number 1), I'd definitely use 'bigger' and 'smaller' instead.'' The ideas of 'taller' and 'shorter' strike me as really weird in the context you described.

Answer

Think of it like this: "tall" and "short" refer to vertical dimensions, whereas "high" and "low" refer to location.
For example, a person who is 150cm tall is short, while someone who's 200cm tall is tall. Both people would by high if they were on a tall mountain.

A tree 25 metres tall would be tall. It would be high if it was next to a cliff, and a short person would be high if they were sitting a the top of that tree.

Since "tall" only refers to vertical height, you'd use "long" to describe a snake.

Skyscrapers are tall buildings. Floors towards the bottom of that skyscraper would be low, whereas floors higher up would be high. Likewise, a fence can be tall or short (whereas a cat sitting on that fence would be high). It sounds odd to call a building or fence "high".