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Nightcrawlers

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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, conical bumps randomly distributed through the lawn.
  • Tolerate nightcrawlers whenever possible, and do NOT apply pesticides.

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.

Brownish-pink worm on the grass

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

  • Occur during early to mid-spring, but can remain throughout the summer

Damage caused by nightcrawlers

An earthworm next to a dark brown pile of soil and earthworm excreta
Mound created by earthworm
Brown mounds of earthworm castings all across the green lawn
Mounds of earthworm castings all across the lawn

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

  • They deposit castings at their burrow entrances forming conical 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 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 a 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.

How to protect your lawn from nightcrawlers

Nightcrawlers keep the soil healthy and offer more benefits than the problems due to their mounds. Low nightcrawler populations impact the long-term health of turf. Control methods should be used, only when needed.

  • Just wash or sweep off nightcrawlers, 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 night crawler 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.

CAUTION: Mention of a pesticide or use of a pesticide label is for educational purposes only. Always follow the pesticide label directions attached to the pesticide container you are using. Remember, the label is the law.

Vera Krischik, Extension entomologist and Mark Ascerno, former Extension entomologist

Reviewed in 2018

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