Interactions of Exotic Earthworms and Millipedes

Snyder, Bruce

"An exotic earthworm invasion is taking place in the southwestern corner of the park. The earthworm was positively identified as Amynthas agrestis, an aggressive invader originally from Southeast Asia. This invasion front was proceeding into the Park at ~12m/yr during 2006 but was greatly affected by drought in late 2006 and 2007 and was found to recede toward a roadside edge of Park. Millipedes collected during 2006 and 2007 in association with this invasion showed a negative impact of A. agrestis invasion on millipede species richness and density. Earthworm invasion also decreased the depth of partially decomposed organic soil horizons at the field site. These findings were supported by laboratory studies, which found that A. agrestis presence greatly decreases survival of millipedes. Native earthworms do not appear to be negatively impacted by the invasion. During 2007 they also located several other places where A. agrestis has invaded, and documented two exotic millipede species in the Park. He has found published a list of 62 species in 21 families and 10 orders. Several undescribed millipede species are also known and will be described in the coming years. PI collected worms in 2012 as part of a larger phylogenetic study involving sampling across 14 States in the Southeast and Midwest. They sampled primarily streambeds and nearby litter and logs. Individuals of the genus Sparganophilus (stream bed dwellers), and from the native genera Bimastos and Diplocardia were collected and analyzed for DNA content, as were specimens of non-native specimens of Amynthas hupeiensis. PI is also addressing questions about the dietary flexibility of the different worms relative to different stages in their life cycles, with the main question being whether Amynthas spp. will switch from leaf litter as a food source to soil at different stages in their development."