( ( When ( ( the ( air bubble ) ) ( is ( large enough ) ) ) ) ( , ( ( the spider ) ( ( settles ( into it ) ) . ) ) ) )
(ROOT (S (SBAR (WHADVP (WRB When)) (S (NP (DT the) (NN air) (NN bubble)) (VP (VBZ is) (ADJP (JJ large) (RB enough))))) (, ,) (NP (DT the) (NN spider)) (VP (VBZ settles) (PP (IN into) (NP (PRP it)))) (. .)))
When the air bubble is large enough, the  spider settles into it.
(ROOT (S (NP (DT An) (JJ underwater) (NN spider)) (VP (VBZ uses) (NP (JJ shiny) (NN air) (NN bubble) (S (VP (TO to) (VP (VP (VB breathe)) (CC and) (VP (VB keep) (ADJP (JJ alive)))))))) (. .)))