Plants and Worms

Since 1998, two studies examining the effects of exotic earthworm invasion on plant diversity and tree seedling abundance have been conducted the Chippewa National Forest in northern Minnesota and the Chequamegon National Forest in central Wisconsin (See the Research section for more details).

close up of forest floor covered with a variety of plants with a few patches of soil in between
Typical understory plant community in a sugar maple forest before earthworm invasion.
Brown soil and leaves with a few tufts of grass
An extreme example of the remaining understory plant community in a sugar maple forest after earthworm invasion.

Different plant species respond to earthworm invasions differently. Some native plants appear to be very sensitive, so much so, that they can rapidly disappear when earthworms invade a forest. Some examples of these plants include…

Life Form Latin (scientific) name         Common Name
Herbaceous plants      Aralia nudicaulis Wild Sarsaparilla
  Aralia racemosa Spikenard
  Streptopus roseus Twisted Stalk
  Uvularia sessilifolia Wild Oats
  Uvularia grandiflora Large-flowered Bellwort
  Polygonatum pubescens or
Polygonatum commutatum
Solomon’s Seal
  Aster macrophyllus Virginia Waterleaf
  Hepatica americana Round-lobed Hepatica
  Trientalis borealis Star Flower
  Thalictrum dioicum Early Meadow Rue
Ferns - Fern Allies Lycopodium obscurum Round-branched Ground-Pine
  Dryopteris species Shield-Fern
Tree Seedlings Acer saccharum Sugar Maple
  Acer rubrum Red Maple
  Ostrya virginiana Ironwood
  Quercus rubra Red Oak
  Tilia americana Basswood / Linden
Shrubs Amelanchier species Serviceberry


In contrast, there are a few native plants species that do very well in the wake of earthworm invasions. Such as:

Life Form Latin (scientific) name         Common Name
Herbaceous plants      Arisaema triphyllum Jack-in-the-pulpit
  Smilacina racemosa False Solomon’s Seal
Grass-like plants Carex pensylvanica Pennsylvania sedge
Tree Seedlings Fraxinus species Ash


The reasons for the different responses by different plant species to earthworm invasion is not completely clear, but evidence suggests that several other factors contribute to the affects we see following earthworm invasion including:

  • changes in mycorrhizal fungi communities
  • the impact of deer herbivory may increase after earthworm invade
  • secondary compounds that may protect plant roots
  • changes in the seedbed conditions
  • changes in light levels on the forest floor
  • other exotic species may be facilitated by earthworms

But I thought earthworms were good for plants!?

We know, anecdotally, that many native plants of the hardwood forest can grow in soils with earthworms since we grow them in many of our gardens. However, recovery of the native understory plant species and tree seedling regeneration following earthworm invasion has not occurred in most invaded forests, even sites in the southern parts of Minnesota that have been invaded for a decade or more. The factors that might prevent recolonization of understory plant species could include the loss of appropriate germination or rooting environment when the duff layer is eliminated. Earthworms may graze on the plant roots and eat seeds in the soil. The rate and intensity of disturbance associated with an advancing leading edge may be so severe as to eliminate the standing populations of most understory species and with no local seed source the plant populations cannot reestablish. More research in this area is needed.