What Is the Gray Bug Found Under Bricks & Dirt?

Updated February 21, 2017

You are likely to find a variety of organisms if you lift a brick up out of your patio or your garden. Some of the most common types of bugs are small, grey bugs that look like little armadillos. These are known as pill bugs or woodlice, a type of wood lice.


Common pill bugs, or Armadillidium vulgare, are also known as woodlice, pill woodlice, or the colloquial roly polies. They are isopods, meaning that they are actually crustaceans, that are found all over the United States and much of Europe hiding under bricks within gardens. They are typically grey, but can be white, as well. They are small bugs and often reach less than an inch in length.


Pill bugs use gills to breathe, which is why they are found in areas with high humidity and moisture. They are often found under bricks within the moist soil, but may also inhabit rocks or potted plants. They roll up into a ball when they feel threatened, thus their "roly polie" nickname.


The bugs are omnivorous and feed off decaying organic matter, most notably plant matter. They are scavengers and will eat both dead plants and dead animal remains. They will occasionally, though rarely, eat live plants. They will also eat algae and lichen from tree barks. They are nocturnal and will emerge at night to feed.

Relationship with Humans

Pill bugs are essentially harmless to humans. Large populations can damage plants or gardens, but this typically only happens in southern states or greenhouses. The bugs may be kept as pets in home tanks. They require high humidity to survive, as well as a steady supply of vegetation for food. They may live up to three years in captivity.


Pill bugs are eaten by a variety of small animals including frogs, newts, toads, spiders and small mammals. The bugs may become susceptible to cannibalism when they moult, or shed their old exoskeleton. Their new exoskeleton will be soft until it hardens, during which time they are soft enough to be eaten by their own kind.


Pill bugs may reproduce sexually or asexually via parthenogenesis, which does not require the female to have a male partner. They lay several dozen eggs that hatch within three to nine weeks. The babies remain in their mother's pouch until they are big enough to leave, at which point they go through four or five moltings before they reach adulthood within a year.

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About the Author

Brenton Shields began writing professionally in 2009. His work includes film reviews that appear for the online magazine Los Angeles Chronicle. He received a Bachelor of Science in social science and history from Radford University.