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Often students come into the classroom understanding the roles of plants and mammals in ecosystems. They understand that there are both biotic and abiotic resources that these organisms need to survive, which can in turn impact the distribution of these species. But what about invertebrates? Little thought is given to earthworms-ecosystem engineers that have changed the face of our North American forests with their introduction.
Scientists and anglers have long extracted earthworms from the soil. This has been done by simply digging up layers of sediment or even pouring soapy solutions over the soil. However, it is more common that earthworms are coaxed to the surface with a solution of dry mustard powder and water. The mustard acts as a mild irritant, drawing worms to the surface. The earthworms can then be rinsed with nonchlorinated water and added to bait buckets or set aside for sampling.
In this lesson, students will use the mustard extraction technique to collect earthworms and determine the impact that resource availability has on their abundance. Research questions are driven by students' own inquiry, giving students ownership of the learning process.
Earthworm basics
Earthworm species play a significant role not only in soil formation and aeration, but also in nutrient cycling, climate regulation, pollution remediation, and primary production (Blouin et al. 2013). Yet, the hardwood forests of North America have changed dramatically with the introduction of earthworms by European settlers in the soils of crops coming from Europe (Hale 2013). Forests once had a thick coating of "duff," a layer of decomposing plant and animal materials above the soil's A-horizon, but earthworms have accelerated the rate of duff decomposition through consumption and mixing of soil layers. The once thick duff layer supported germination of a number of native plant species, but with its loss, ground-dwelling organisms such as the blue-spotted salamander and the ovenbird have lost valuable habitat (Hale 2013).
To get students started with this activity, we think it is important for them to recognize the role earthworms have in shaping our forests. This can be done by showing students the dramatic before and after photos of forests that have been impacted by earthworm invasion. A number of these images can be found online, including on the Great Lakes Worm...