Centipedes and millipedes are arthropods belonging to the subphlyum Myriapoda. They occasionally enter homes in search of shelter, moisture, and food. While these many-legged critters are not harmful to humans, their appearance can be unsettling.
House centipedes don’t cause damage to belongings or stored food, nor do they attack people or pets (although they may bite in self-defense in rare cases).
In fact, they are considered mostly beneficial because they only hunt other pests like cockroaches, spiders, and ants.
House centipedes are seldom seen because they are nocturnal and are quick to flee when people are around. They usually enter homes during the winter and hide out in cool, dark, and humid areas in basements and bathrooms.
Size: 1–1 3/8 inch long (25–35 mm); may appear 3–4 inches long if including legs and antennae
Color: Yellowish-gray or light brown
Shape: Elongated, flattened body with prominent antennae and 15 pairs of long legs
Legs: 15 pairs of long legs with light and dark stripes; one pair per body segment; last pair is modified to look like antennae
Antennae: Long, thin antennae that are nearly twice the length of body
Head: Flat head with well-developed eyes, jaw-like mandibles, and modified pincer-like legs (forcipules)
Body: Elongated, flattened body with 3 dark stripes running longitudinally down its back
Greenhouse Millipede / Garden Millipede
Greenhouse millipedes are usually found outdoors in moist, shady locations like gardens, flower beds, and compost piles.
They’re most commonly seen in the summer when it’s hot and dry, forcing them to enter homes in search of moisture. Heavy rainfall can also prompt them to seek shelter indoors. Once inside, they tend to invade cool, dark areas like basements and crawl spaces.
These millipedes are harmless to humans, although they release a foul-smelling odor when alarmed.
Size: 3/4–7/8 inch long (19–22 mm); about the length of a penny or a nickel
Color: Light to dark brown
Shape: Long, cylindrical-like body with short antennae and many pairs of short legs
Legs: Short, pale, cream-colored legs; 2 pairs per body segment; adds new body segments as it grows and molts until it has 30 or 31 pairs of legs (females have 1 more pair than males)
Antennae: Short, segmented antennae
Head: Rounded head with no eyes
Body: Long, cylindrical body with up to 20 segments (body rings); each segment has a transverse groove across the back and a pale, cream-colored plate-like extension (paranotum) on each side