Infest
Definition 1 of 2
Pro Tip 1/3
Negative Connotation
Infest usually implies a situation is serious and the creatures or things are causing harm. The lake was infested with harmful algae.
Pro Tip 2/3
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.
Pro Tip 3/3
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.