IPA: /əˈswɔrm/
KK: /əˈswɔrm/
Filled with a large number of moving things or people; crowded or overflowing.
The garden was aswarm with butterflies during the spring.
Aswarm is formed from the prefix "a-" (meaning in a state of) and "swarm" (from Old English "swearm", meaning a group of insects or animals). The word "aswarm" means to be in a state of being swarmed or filled with a large number of things, typically insects.
Think of being 'in a state of' ('a-') being surrounded by a 'group' ('swarm') of insects — that's why aswarm means to be filled with many things.