Since the gerund and the present participle have the same forms, sometimes it is difficult to decide whether an -ing form in a sentence is a gerund or a participle.

He insisted on my tidying my room.
He insisted on me tidying my room.

At a closer look, however, we can see that in the first sentence tidying is preceded by a possessive adjectiveA part of speech that modifies, qualifies or restricts a noun or a pronoun. E.g.: The apples are ripe. ("ripe") (my), so this -ing form is a gerund, as it functions as a nounA part of speech that names a person, place or thing. E.g.: The koala is a marsupial. ("koala", "marsupial"). In this sentence the objectA person or thing that is affected by the action of a verb or involved in the result of an action. of the verbA part of speech that expresses an action or a state. E.g.: John seldom plays tennis. insist on is my tidying my room.

In the second sentence, the object of insist on is me (the accusative for I) and tidying is a present participle modifying the pronounA part of speech that refers to or stands instead of a noun. E.g.: Who do you think I am? ("you", "I") before it.

For most native speakers the two sentences mean exactly the same. (As hairsplitters, though, we would still say that in the first sentence the focusThe main or central point of attention or interest; what is emphasized. E.g.: All I wanna do is have some fun. ("all") is on tidying, and my modifies it, while in the second the focus is on me and tidying modifies it.)

In some cases it is only a matter of interpretation and not form (as above) whether an -ing form is a gerund or a present participle:

Hunting lions can be dangerous.

If hunting is a present participle, the sentence will mean: lions that hunt can be dangerous. If it is a gerund, the sentence means: it can be dangerous to hunt lions.

Other structures followed by the gerund
The use of non-finite forms Verbs followed by TO + infinitive or the gerund