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Quick facts about nightcrawlers

  • Nightcrawlers are beneficial earthworms that provide natural aeration of soil.
  • They allow water and oxygen to penetrate more easily into the ground.
  • Their feeding and excrement helps recycle nutrients and fertilize the soil.
  • If there are nightcrawlers in your lawn, you will notice small, cone-shaped bumps randomly distributed through the lawn.
  • Tolerate nightcrawlers in your lawn whenever possible, and do NOT apply pesticides.

Earthworms, including nightcrawlers, are an invasive species but not regulated in Minnesota. They are monitored on Great Lakes Worm Watch. Never release them into natural woodland areas or lakes.

Live and dead plant material can accumulate at the soil surface and reduce the penetration of water and fertilizer into the soil. Nightcrawlers get rid of this layer and help aerate the soil.

How to identify nightcrawlers

  • 4 to 8 inches long and reddish-brown.
  • They tunnel in the soil and may come up to the surface on rainy days especially during spring.
  • Are seen during early to mid-spring, but can remain throughout the summer.

Damage caused by nightcrawlers

Mound created by earthworm

Nightcrawlers and other earthworms are considered invasive species and damage forest floors. Never release an earthworm in a natural forest. If you use them for fishing bait, throw away any unused worms in the trash.

Nightcrawlers are beneficial to lawn health but can leave behind a waste product called castings.

  • They deposit castings at their burrow entrances forming cone-shaped mounds at the soil surface.
  • Mounds do not harm the turf but this lumpiness can be a nuisance to home lawns, athletic fields and golf courses.
  • Mounds are most common in early to mid-spring when nightcrawlers are first active.
  • In late spring and summer, when the weather becomes warmer, nightcrawlers move deeper into the soil and are not normally seen.

You may see nightcrawlers moving away from the lawn when the lawns are overwatered or after heavy rainfall.

They become a nuisance when they are found in large numbers on sidewalks, driveways, patios, pools and other places where they are not wanted.

Mounds of earthworm castings all across the lawn

How to manage nightcrawlers

Nightcrawlers keep lawn and garden soil healthy and offer more benefits than problems. Control methods should be used only when needed.

  • Wash or sweep off nightcrawlers into the lawn, if you see larger numbers on sidewalks, driveways, etc.
  • If you ignore them, they will eventually move off on their own or dry up and die.
  • Never use a pesticide on nightcrawlers.

Vertical mowing

This method removes the lumpiness of mounds and reduces the amount of food available for nightcrawler development.

  • Vertical mowing is best done in late summer, mid-August through September.
  • Do not do vertical mowing in hot weather as it causes stress to the lawn.

You can also power rake in spring once the ground is firm underfoot and before hot weather sets in.

If you power rake in spring, apply a pre-emergent herbicide to prevent annual weeds from sprouting.

Authors: Vera Krischik, Extension entomologist and Mark Ascerno

Reviewed in 2021

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