
Infest
Negative Connotation
Infest usually implies a situation is serious and the creatures or things are causing harm.
The lake was infested with harmful algae.
Large Numbers
Use 'infest' when there are many pests or unwanted things, not just one or a few.
The old barn was infested with bats.
Undesirable Presence
'Infest' is used when the creatures or things are unwelcome and usually difficult to remove.
The park has been infested with invasive species.