Here's why:
* Present participles are verb forms ending in "-ing". They can function as:
* Adjectives: describing a noun (e.g., "The swarming bees were a sight to behold.")
* Verbs: part of a verb phrase (e.g., "The bees are swarming around the hive.")
* Nouns: representing an action (e.g., "The swarming of the bees was impressive.")
The part of speech of "swarming" depends on its function in the sentence.