Use Termagent Swarm's power as it last existed on the battlefield to determine the number of tokens you create.

The triggered ability that checks to see if X is 5 or greater refers to the value of X that was chosen as the spell was cast, which may be different from the number of counters it entered with if there are replacement effects involved. This is also true for any other ability that it has which refers to X and triggers when it enters the battlefield.

See also "New Keyword Ability: Ravenous" in General Notes.

If a permanent spell with ravenous is copied, the copy will have the same value for X, and the token permanent that the spell becomes as it enters the battlefield will enter with X counters.

If another permanent enters the battlefield as a copy of a creature with Ravenous, it will not enter with any counters from the ravenous ability.

A creature with ravenous gets its counters as it enters the battlefield. It doesn't enter the battlefield first and then get its counters. Any triggered ability that looks for a creature with a certain power or toughness entering the battlefield will see the counters when it checks to see if it should trigger.