The recent attention earthworms are receiving in local media is primarily due to moist soil conditions and moderate temperatures. From home lawns, gardens, and flower beds to highly maintained sports fields, earthworms are a common fixture in our soils. It may come as a surprise that ALL of the earthworms that we see in New York soils today are of European or Asian descent. Advancing glaciers during the last ice age led to the demise of native earthworms in many Northeastern and Midwestern states. Because earthworms disperse very slowly (30 feet per year), native earthworms are still absent in their original northern ranges. In contrast, exotic earthworms have likely been present in our soils since the first potted plants were brought to North America, and the use of these worms in fishing and composting has facilitated numerous, repeated introductions into otherwise earthworm-free environments.
There is a lot of conflicting information out there on the role of earthworms in turf soils. Earthworms fall into the category of “ecosystem engineer”, or, any organism which creates or modifies its environment. Within the turfgrass landscape, earthworms play a large role in the decay of detritus (thatch, tree leaf litter, and dead roots). Earthworms mix organic matter into mineral soil, improve aeration and water infiltration rates, and promote microbial activity and soil aggregation. Yet, earthworms can also have negative impacts on turf systems; many deposit their fecal material (casts) upon the soil surface, affecting playability on golf courses. As decomposers, earthworms are generally beneficial; however, they are also capable of accelerating decay beyond the rate at which litter accumulates. In such cases, the entire litter layer disappears, and only bare soil remains. This can reduce the temperature and moisture buffering capacity of soil, suppress plant germination, and reduce densities of other beneficial soil animals. Other earthworm-driven problems in turf include earthworm foraging by mammals and birds which can be easily confused for “grubbing” activity and earthworm channels also serve as macro-pores where applied nutrients and pesticides can move past the turf rhizosphere.
Management efforts to control earthworms are generally discouraged as such actions can have negative non-target effects on other beneficial soil invertebrates including less -damaging worm species . In addition, damage thresholds do not exist for earthworms in NY State. Cultural and biologically based control methods that have been studied include aeration, heavy rolling, soil acidification, and soil flushes containing earthworm irritating compounds (tea seed extracts and jugonal from Black Walnut), however, there appears to be no single solution that is effective in all cases. For example, while most invasive earthworms respond negatively to soil acidification, others, such as the genus Amynthas (e.g., Alabama jumpers), are quite tolerant of acidic soils.
Should we be concerned? In New York, multiple species of exotic earthworms are coexisting in turf soils , and while all can be categorized as ecosystem engineers, there are many subtle differences in their biology , and the simple presence of earthworms (even in high numbers) may not translate to actual problems in turf. It is also important to consider the beneficial ecosystem services that will disappear if earthworms are removed. While the jury is still out as to whether the benefits of earthworms outweigh the detriments, most experts agree that preventing future introductions of exotic earthworms is the most feasible method for thwarting future earthworm-driven problems in turf and ornamental systems. Efforts to do so may include destroying leftover fish bait, minimizing the transport of mulch and yard waste, and freezing composts and mulches before use.
— Kyle Wickings, Cornell University Turfgrass ShortCutt