Millipedes, Centipedes, Sowbugs & Roly-Polys - Friend or Foe?

By on June 09, 2011

Some insects you will see out in the garden-but generally not harmful

Centipedes, millipedes, sow bugs, and pill bugs or roly-polys are unusual arthropods. Sow bugs and pill bugs are actually crustaceans (related to shrimp, crabs, and lobsters).

None of these pests transmit diseases to plants, animals, or humans. They don’t damage furnishings, homes, or food—but they can frighten people.

Millipedes

Some folks confuse millipedes with centipedes. These two groups of many-legged, creepy-crawlies belong to different arthropod classes. The obvious differences:

  • Millipedes have 2 pairs of legs per segment, a feature that gave rise to its class name of Diplopoda.
  • Centipedes only have a single pair of legs per segment.
  • Millipedes are vegetarians while centipedes are carnivores.

Get a load of those legs

The name MILLIPEDE comes from the Latin word mille, meaning a thousand, and pedis, meaning foot. While these creatures do have a lot of legs, none actually have a thousand. There are lots of species (6,000+) and the number of legs varies considerably. One source says the highest number of legs known for any millipede is 710.

A millipede can live from 5 to 7 years. They are detrivores, which means they eat dead and decaying plant matter. These little beauties produce new legs almost every time they shed their exoskeletons. They give off a strong-smelling, stomach-irritating chemical when interfered with. If eaten they cause vomiting.

Being vegetarians, millipedes eat plant matter

Some feed on decomposing vegetation and fallen fruit while others will occasionally damage seedling plants by consuming stems and leaves. They eat all kinds of potatoes, flower bulbs, and tubers. They live in the garden in areas of moist mulch, compost, and lawn thatch. The females lay between 50 to 100 eggs a year and live for about 3 years.

Millipedes have a tendency to wander indoors in the late fall, in search of somewhere to overwinter.

BLACK MILLIPEDE (Tachypodiulus niger) looks like a length of black, armoured pipe and coils stiffly like a watch spring.

SPOTTED MILLIPEDE (Blaniulus guttulatus) has a row of reddish spots along each side of its yellow body.

Centipedes

Centipedes are worm like, with flattened bodies.  They belong to a group called Chilopods. Color can be brown, gray, red, or greenish-blue. with many body segments. Most of the body segments have one pair of legs. Centipedes are fast runners and may vary in length from 1 to 6 inches. They have one pair of antennae or “feelers” that are easily seen. Centipedes have poorly developed eyes and are most active at night. They are predators and feed mainly on insects and spiders.

Best rule of thumb? Never handle centipedes.

Centipedes do have the first pair of appendages modified into claws, which can inject poison through their venom glands, which they use to immobilize their prey. The larger centipedes can bite people and they emit an irritating fluid that can cause an allergic reaction.

Centipedes prefer moist, protected habitats

They are delighted with spaces under stones, rotted logs, leaves, or bark. They spend the winter as adults and lay eggs during the warm months. Indoors they may be found in closets and bathrooms where there is high humidity.

They usually lay 15-55 eggs clustered together, although the eggs of some species are laid alone. Eggs are usually laid in soil and covered by a sticky substance; they hatch soon after they are deposited. The female will usually guard the eggs and the newly hatched young. Young centipedes closely resemble the adults and require 3 years to mature. Centipedes may live up to 6 years.

Sow bugs & Pill bugs

Sow bugs and pill bugs (both also known as woodlice) are terrestrial crustaceans, and are related to lobsters, shrimp and crayfish. They are the only crustaceans that have adapted to living their entire life on land and they still have gills.

The habits, biology, and control of sow bugs and pill bugs are similar. Both animals are slow-moving, crawling arthropods. They need a moist environment and are most active at night. During the day they rest under trash, rocks, boards, decaying vegetation, or just beneath the soil surface.

Pill bugs roll up, sow bugs can’t

The main differences between a sowbug and a pillbug:

  • The sowbug possesses two tail-like appendages, seven pairs of legs, and well-developed eyes. They are incapable of rolling into a tight ball.
  • Pill bugs or “roly-polys” lack the tail-like appendages and can roll into a tight ball or “pill” shape when disturbed.

In both species breeding can occur throughout the year in mild climates. The female carries the eggs in a brood pouch on the underside of her body, with up to 200 eggs per brood. The eggs hatch in 3 to 7 weeks and the young remain in the pouch another 6 to 7 weeks.  Some species produce only one brood per year, but others may produce 2 or more. Individuals may live up to 3 years.

What they eat

At night they venture out and feed on decomposing organic material. They will feed on the tender foliage, stems and roots of young garden vegetable transplants, seedlings, and bedding plants. They also rasp the outer skin of cucumbers lying on the ground in gardens,  causing fruit to be deformed and blemished.

Mainly a nuisance, pillbug and sowbug control in the garden is not always necessary, as they cause little harm to plants. In fact, most gardeners do not categorize them as pests, but think of them as beneficials for converting decayed vegetation into humus.

However, if you notice pill bugs or sow bugs feeding on tender seedlings, you can refer to our list of Insecticides for controlling them.

Ways to Control

Unless these guys are causing damage to your plants, they are ok to not bother them. But if you feel they are causing damage, look for natural insecticides that are labeled for these pests.

Here are a few methods that can be tried to control millipedes, centipedes, sow bugs, and pill bugs in the garden organically without the use of pesticides:

  • Reduce moist areas in the garden where eggs overwinter.
  • Rake out old mulch under plants and replace it with fresh mulch or straw.
  • Move piles of leaves to a compost pile away from areas you want to keep insect free.
  • Aerate your lawn to reduce thatch that could provide a damp home.
  • Pour wood ash into their nest area to dry out soil and create an uninhabitable area. Be careful because a large amount of wood ash is toxic to your soil and garden.

Chickens are great biological control for millipedes, centipedes, sow bugs, and pill bugs, as well as a wide variety of other pests. Chickens are voracious eaters and spend most of their day wandering around looking for little moving critters they can eat.

Control Millipedes, Centipedes, Sow bugs and Pill bugs Indoors

A heavy infestation indoors usually indicates a large population outdoors. To keep millipedes, centipedes, sowbugs and pillbugs from coming indoors, move their habitats (compost piles, firewood, and stones) away from the house. Items that cannot be removed should be elevated off the ground. Create a band of gravel between your house foundation and flowerbeds.

All these arthropods require moisture and do not survive indoors for more than a few days. Sweep them up with a broom or vacuum them. To combat serious infestations, seal cracks in your outside foundation, and around the bottoms of doors, and basement windows.

Not So Bad

Though they may “freak us out”, millipedes, sow bugs, and pill bugs assist us by eating decomposing matter. The centipede eats aphids and other soft-bodied insect pests.  Unless they are actually damaging your young seedlings, it is not necessary to do anything to control their populations.

Some folks have taken to making millipedes pets!  There is always something new and fascinating when it comes to nature.

Photo Credits

  • Armadillidium vulgare by Joseph Berger, Bugwood.org
  • Porcellio scaber by Joseph Berger, Bugwood.org

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