infest

American  

[in-fest] / ɪnˈfɛst /

verb (used with object)

1. to live in or overrun to an unwanted degree or in a troublesome manner, especially as predatory animals or vermin do.

   I had a major problem with cockroaches infesting my kitchen.

   The emerald ash borer has already infested many of the local ash trees.

2. to be numerous in, as anything undesirable or troublesome.

   the cares that infest the day.

3. Archaic. to harass.

---

infest British  

/ ɪnˈfɛst /

verb

1. to inhabit or overrun in dangerously or unpleasantly large numbers

2. (of parasites such as lice) to invade and live on or in (a host)

---

Other Word Forms

• infestation noun
• infester noun
• reinfest verb (used with object)

Etymology

Origin of infest

First recorded in 1375–1425; from late Middle English, from Latin infestāre “to assail, molest,” from infestus “hostile”

Explanation

The verb infest means to invade in large number, often resisting control and causing damage or hardship. Bedbugs can infest people's belongings and even their bodies, or mice may infest your kitchen if you leave the cheese out too often. Infest comes from Latin: in- means "not" and festus means "able to be seized." So infest describes something is not able to be seized, typically because it's present in such large numbers. For example, mosquitoes may infest your backyard during the summer and annoy you when you're trying to relax. Infest is usually used to describe pests, such as bugs or rodents, that overrun something in such large number that they are difficult to control.

Example Sentences

An infestation occurs when fly maggots infest the living flesh of warm-blooded animals, the CDC says.

From Los Angeles Times • Sep. 17, 2025

But it's not technically possible for them to infest their own home.

From Salon • Jul. 21, 2024

A parasitic worm that can infest the brains of moose appears to be playing a role in the decline of the iconic animal in some regions of North America.

From Science Daily • May 15, 2024

For example, the oak processionary moth, whose caterpillars infest oak trees, thrive in these shorter cold spells making the oaks more vulnerable to attack from other parasites, he says.

From BBC • Dec. 26, 2023

With insects that infest crops the story is the same.

From "Silent Spring" by Rachel Carson