The question of whether native earthworms exist in Alaska is complex and somewhat uncertain. While there is evidence suggesting that a native species might be present, the details are not entirely clear.
1. Native Earthworm Species
The earthworm species potentially native to Alaska is Bimastos rubidus. According to Jerry Minnich in The Earthworm Book (Rodale Press, 1977), this species is among the few recorded natural earthworms in Alaska. Of the approximately 1,800 known earthworm species, Bimastos is considered one of the smaller varieties.
2. Challenges for Earthworms in Cold Climates
Earthworms are cold-blooded, which means their activity decreases significantly as temperatures approach freezing. Species living in regions where soil freezes are vulnerable to sudden fall frosts unless they have adequate mulch cover to insulate against freezing. Earthworms generally prefer to burrow deeply to remain below the frost line, but those in frozen soil can survive winter conditions if the soil is not permafrost. Permafrost areas are not conducive to earthworm survival.
3. Invasive Earthworms in Alaska
In Alaska, most earthworms encountered are likely invasive species. These earthworms were probably introduced through plant soils or fishing bait. Studies show that four out of five documented earthworm species in Alaska originated from Europe or Asia. The fifth species might be native to North America and could have survived the last ice age in Interior Alaska, a region that was not covered by glaciers during the Pleistocene Era.
4. Enchytraeidae: The Alternative to Earthworms
In addition to earthworms, Alaska hosts species from the family Enchytraeidae, which are not classified as true earthworms but fulfill similar ecological roles. Enchytraeidae are microdriles, small worms that are mostly aquatic or semi-terrestrial. They resemble small earthworms and include terrestrial species known as potworms that thrive in highly organic environments.
Mesenchytraeus: Known as “ice worms,” this genus lives primarily within glaciers and surfaces only during specific summer periods.
Grindal Worm (Enchytraeus buchholzi): This species is commercially bred as aquarium fish food.
Conclusion
While Alaska may have some native earthworms like Bimastos rubidus, most earthworms found in the region are invasive. Enchytraeidae species also contribute to soil health by performing similar functions as earthworms. Understanding the presence and roles of these organisms is crucial for managing soil health and ecosystems in Alaska.
