The difference between Insidious and Subtle

When used as adjectives, insidious means producing harm in a stealthy, often gradual, manner, whereas subtle means hard to grasp.

check bellow for the other definitions of Insidious and Subtle

Insidious as an adjective:

Producing harm in a stealthy, often gradual, manner.
Insidious as an adjective:

Intending to entrap; alluring but harmful.

Examples:

"Hansel and Gretel were lured by the witch’s insidious gingerbread house."
Insidious as an adjective (nonstandard):

Treacherous.

Examples:

"The battle was lost due to the actions of insidious defectors."

Subtle as an adjective:

Hard to grasp; not obvious or easily understood; barely noticeable.

Examples:

"The difference is subtle, but you can hear it if you listen carefully."
Subtle as an adjective (of a thing):

Cleverly contrived.
Subtle as an adjective (of a person or animal):

Cunning, skillful.
Subtle as an adjective:

Insidious, deceptive, malicious.
Subtle as an adjective:

Tenuous; rarefied; of low density or thin consistency.
Subtle as an adjective (obsolete):

Refined; exquisite.