Learn Hardcore Spanish (Latin America): Cuando suba la marea, los cangrejos se esconderán bajo la arena. - When the tide rises, the crabs will hide under the sand.

Because the clause introduced by cuando refers to an action that hasn’t happened yet (the rising tide). In Spanish, temporal clauses about future or uncertain events take the subjunctive. If it were a habitual or past event, you’d use the indicative instead.

Can I also say cuando la marea suba instead of cuando suba la marea?

Yes. Spanish allows both word orders. Moving la marea before suba doesn’t change the meaning—it only shifts the emphasis slightly. Both are perfectly natural.

Why does the sentence use se esconderán instead of just esconderán?

Because the verb here is esconderse, a pronominal (reflexive) verb meaning “to hide oneself.” The se indicates that the subject (the crabs) is doing the hiding on itself.

How is the future tense formed and when do I use it?

The simple future in Spanish is formed by adding endings (-é, ‑ás, ‑á, ‑emos, ‑éis, ‑án) directly to the infinitive: for example esconder → esconderán (they will hide). You use it to talk about actions that will happen in the future or to express probability (“¿Qué hora será?” – “I wonder what time it is.”).

What’s the difference between bajo and debajo de when saying “under”?

Both can mean “under,” but:

bajo is a straightforward preposition used directly before the noun (as in bajo la arena).
debajo de is a compound preposition that often stresses position (“underneath”) and always requires de before the noun.
In this sentence, bajo la arena is shorter and more idiomatic.

What does marea mean in this context?

Marea means “tide,” the regular rise and fall of the sea level. Here, subir la marea means “the tide rises” (high tide).

Could I use the present tense here, as in cuando sube la marea, los cangrejos se esconden?

Yes—but that would turn it into a general or habitual statement (“Whenever the tide rises, crabs hide”). If you want to describe one specific future event, you need the subjunctive + future combination as in the original sentence.

Can I swap the clauses and say Los cangrejos se esconderán bajo la arena cuando suba la marea?

Absolutely. Spanish allows the subordinate clause (the “cuando…” part) to come before or after the main clause. Placing the main clause first often sounds more direct or conversational.