2012 NORTHEASTERN NATURALIST 19(2):313–322 Asian Invasive Earthworms of the Genus Amynthas Kinberg in Vermont Josef H. Görres1,* and Ryan D.S. Melnichuk1 Abstract - We are reporting on established populations and sightings of species in the genus Amynthas in Vermont, from Quechee (43°38'N) central-eastern Vermont to Alburgh (44°58'N) on the northwest border to Canada. To our knowledge, these are the first sightings of Amynthas spp. reported for Vermont. Invasive Asian earthworms of the genus Amynthas were found at three of twelve forested locations surveyed for invasive European earthworms. In addition, Amynthas was found in a number of horticultural settings. We evaluated soils and climate information for forested sites with Amynthas in Vermont and compared climate with the original range and more southern US sites. Our findings suggest that Amynthas may expand its range even further north than Vermont and that the freeze-free period required for maturation is approximately 90 days. Introduction Earthworms became extinct in northeastern North America during the last glaciation but were reintroduced by European settlers (Bohlen et al. 2004). Since then, the invasion of forests by European earthworms has played a significant role in the ecology of northeastern hardwood forests. Earthworm invasions transform and mix O and A horizons, destroying habitat for many indigenous plant species and thus reducing plant biodiversity (Hale et al. 2005, 2006). Now, a new group of earthworms of genus Amynthas, originating in east Asia, are colonizing forests in the northeastern USA (Burtelow et al. 1998) and other cold-climate environments in North America (Callaham et al. 2003, Snyder et al. 2010). These earthworms have the potential to severely impact forest ecosystems (Burtelow et al. 1998). Amynthas have been reported in North America since the 19th century (Gates 1958, Snyder et al. 2010). Their common names include Jersey Wigglers, Alabama or Georgia Jumpers, Snake Worm, and Crazy Worm which refer aptly to their snakelike, fast mode of movement and maybe also to the fracture and shedding of its tail when an Amynthas is caught. There is remarkably little known about their life-history traits. They are classed as epi-endogeic species because they live at the surface or within the top layer of the soils. A few recent studies discuss environmental tolerances (such as temperature, moisture, and acidity) on one species, A. agrestis Goto & Hatai 1899 (Bernard et al. 2009, Richardson et al. 2009, Snyder et al. 2010), but there remain many knowledge gaps about the genus as a whole. The optimal temperature range in lab experiments for mature A. agrestis was between 12 and 25 °C, but survival strongly depended also on soil moisture. A combination of 25 °C and low moisture resulted in 100% mortality as did their exposure to 1Plant and Soil Science, University of Vermont, 258 Jeffords Hall, Burlington, VT 05405. *Corresponding author - jgorres@uvm.edu. 314 Northeastern Naturalist Vol. 19, No. 2 -5, 5, and 35 °C (Richardson et al. 2009). Amynthas agrestis may survive the winter as cocoons (Callaham et al. 2003), but the spatial distribution of mature worms in the field varies as a function of soil and air temperatures and soil moisture from April to October (Snyder et al. 2010), reaffirming the observation by Richardson et al. (2009) that moisture is an important factor. The objectives of this communication is to report on Amynthas in Vermont, document the climate, soil, and vegetation parameters at locations where we found them in Vermont forests, and compare these parameters with those of the original range and other, more southern sites in the eastern USA. Methods We did not survey for Amynthas in a systematic way. Amynthas sites were found during other investigations related to earthworms. In all, we surveyed 12 forested sites from Quechee to St. Albans. We looked at these sites in July and September 2010. The sites included urban remnant forests as well as sites within the Green Mountain National Forest and stretches along the Long Trail, a hiking trail which traverses the State of Vermont from north to south. The three forested sites with Amynthas are in remnant forests at Quechee, Shelburne, and South Burlington. The site in South Burlington is adjacent to a townhouse development that receives horticultural care, and is impacted by storm runoff from the subdivision. The site in Shelburne is located between a road and agricultural land. The site in Quechee is located in a floodplain with ephemeral flooding events. The Quechee and South Burlington sites were selected in 2006 for a study on the invasive Berberis thunbergii DC (Japanese Barberry) and European earthworms. In South Burlington, there are two Amynthas populations separated by 300 m. The Shelburne population was discovered in 2010 while investigating the complete lack of understory plants in a stand of Acer saccharum Marsh (Sugar Maple). At Quechee, the mixed deciduous-coniferous forest is dominated by A. saccharum and Pinus strobus L. (White Pine). The site has a dense understory where B. thunbergii is the dominant shrub. Amynthas is found in two adjacent stands in South Burlington, directly abutting a landscaped townhouse development. One stand is dominated by A. saccharum, the other by P. strobus and Tsuga canadensis (L) Carr. (Eastern Hemlock). In South Burlington, the A. saccharum stand has a sparse understory that includes Trillium undulatum Willdenow (Painted Trillium), whereas the P. strobus/T. canadensis stand has a ground cover of Mitchella repens L. (Partridge Berry). The Shelburne canopy is exclusively A. saccharum with understory plants absent. In Quechee and South Burlington, the soils are fine sandy loams with pH values of 5.5 and 6.2, respectively (Table 1). In Shelburne, Amynthas are found in a silt loam. There, the entire A-horizon is strongly aggregated into castings to a depth of 5 cm, with a pH of 7 and some carbonate content (Table 1). The castings are in direct contact with the B-horizon. There are only a few Megascolecids reported in the northeastern USA. Earthworms were attributed to the genus Amynthas first by their snakelike locomotion 2012 J.H. Görres and R.D.S. Melnichuk 315 and their propensity to jump and wriggle from your hand. We also checked on a couple of external characteristics such as a clitellum that stretches around the circumference of the body as well as setae arrangement and position of male pores (Blakemore 2002). Within the genus, Amynthas species are difficult to discern (Hale 2007), and we did not attempt identification to species, but sent preserved Amynthas individuals from the Quechee site for identification to Dr. S.W. James of the University of Kansas. Where we found Amynthas, we surveyed for other earthworms in June and September 2010 by hand sorting to a depth of 30 cm and by inspecting the soil surface for excavation middens commonly created by Lumbricus terrestris L. (Common Nightcrawler) We collated climate data for the three Vermont forested sites with established Amynthas populations and other cold-climate locations in the eastern USA (Table 1) where they were reported previously (Bernhard et al. 2009, Burtelow et al. 1998, Callaham et al. 2003). Lowest and highest monthly temperature normals and annual average temperature were taken from the closest official NOAA stations (USDC - NOAA 2002). Median early and late freeze dates for threshold temperatures of 0 and 2 °C were taken from the National Climate Data Center (USDC - NOAA 2005) as was monthly average precipitation (USDC - NOAA 2007). Climate data are for the 30-year climate period from 1971 to 2000, hardiness zone data are from the USDA (USDA - USNA 2010), and soils data for the three forested Vermont sites are from NRCS’s Web Soil Survey (USDA - NRCS 2010). When available, soil information for the comparison of sites was gleaned from the publications of reports of Amynthas at other cold-climate sites. In addition, we included climate data from their original range in Japan (www. climate-charts.com 2011a, b). Table 1. Location and soil properties of large Amynthas populations in Vermont and for comparison sites in the eastern USA. "-" indicates no information. Texture: CEC Latitude Longitude Soil Series top 10 cm meq/100 g pH Quechee, VT 43°38'N 72°24'W Hinckley Sandy loam 5.6 5.5 Rumney Fine sandy loam 2.8 6.2 South Burlington, VT 44°25'N 73°12'W Duane-Deerfield Fine sandy loam 3.9 5.5 Shelburne, VT 44°24'N 73°14'W Palatine* Silt loam 10.1 7.0 Brasstown Bald, GA** 34°52'N 83°48'W Soils in the area are sandy loams and loams Madison County, NY** 42°49'N 75°32'W Soil under - residential land use Cary Arboretum, 41°47'N 73°44'W - Silt loam - 5.5+/4.1++ Millbrook NY *1% CaCO3. **Approximate coordinates. +With Amynthas. ++No Amynthas. 316 Northeastern Naturalist Vol. 19, No. 2 Results and Discussion We found established populations of Amynthas with greater than 50 individuals per m2 in three out of twelve forest sites surveyed (Fig. 1, Table 1). However, more systematically conducted surveys may find that these earthworms are more widespread. At Quechee, the earthworms were identified as A. agrestis (S.W. James, Biodiversity Institute, University of Kansas, Lawrence, KS, pers. comm.). The nine sites where we did not find Amynthas were more remote and at greater elevation than the sites in Quechee, Shelburne, and South Burlington. We found European earthworm species only at the Quechee site and the P. strobus stand in South Burlington. These were Aporrectodea spp., Octolasion tyrtaeum Savigny (Woodland White Worm), Lumbricus rubellus Hoffmeister (Red Worm), and Lumbricus terrestris. At the A. saccharum stands in South Burlington and Shelburne, Amynthas was the only earthworm taxon. The three forested sites differed in vegetation and soils, showing that, collectively, genus Amynthas spp. have wide tolerances for forest type. Whether individual species have narrower tolerances is unclear. Soil textures were within the categories reported for Amynthas habitat elsewhere (Burtelow et al. 1998, Callaham et al. 2003, Snyder et al. 2010). The absence of an O-horizon and that Figure 1. Presently verified locations of Amynthas in Vermont. Sites at Quechee, South Burlington, and Shelburne are large populations in woodlands. Other sites are associated with home and institutional gardens. 2012 J.H. Görres and R.D.S. Melnichuk 317 the very shallow A-horizon comprised only of castings suggest very disturbed soils in Shelburne. Interestingly, in both South Burlington and Shelburne, individuals of Amynthas shared decomposing logs with Plethodon cinereus Green (Red-Back Salamander ) but not with other earthworms. The hollow interiors of the logs were filled with earthworm castings, with Amynthas being the likely source as no other earthworms were found at these sites. Until recently, Amynthas species had only been associated with compost (Gates 1958), and some species are available for purchase for this purpose and as bait. Compost operations, horticulture, and fishing may thus be vectors by which these worms spread. Amynthas found in Vermont likely reflect these dispersal mechanisms. Amynthas that we found in horticultural settings were always found in the presence of mulch or compost. We speculate that the presence of Amynthas at three forested sites in Vermont is also consistent with these dispersal mechanisms and the notion that these earthworms colonize disturbed sites (Reynolds 1978). This finding is in contrast to some of the sites examined by Callaham et al. (2003), who found A. agrestis in high elevation and presumably undisturbed locations. Regardless of dispersal mechanism, Amynthas will still have to survive the climatic conditions in Vermont to establish viable populations. Amynthas originated in subtropical and temperate Asia. The range of A. agrestis, one of the common invaders of this genus, includes Japan and Korea (Blakemore 2003, 2008). Amynthas agrestis (included in the species combination Metaphire agrestis [Blakemore 2003]) was reported at the Kii Pensinula, Japan (Sakai et al. 2006), but it occurs as far south as Kyushu Island and as far north as Kunashir Island (Russian Federation), north of Hokkaido (R.J. Blakemore, COE Soil Ecology Group, Yokohama National University, Yokohama, Japan, pers. comm.). These locations have, respectively, a humid hot summer subtropical and humid warm summer continental climate (Peel et al. 2007). The range of A. agrestis in Japan thus encompasses the two climate zones that cover the majority of eastern North America, including Vermont and parts of eastern Canada, potentially extending the range of this species as far north as the Maritime Provinces. The appearance of Amynthas in Vermont is not surprising considering high A. agrestis densities found in other locations with temperature normals and freeze-free periods similar to those at the forested Vermont sites, although the other sites were in different growing zones (Table 2). For example, Burtelow et al. (1998) reported Amynthas Hawayanis Rosa at the Cary Arboretum of the Institute of Ecosystem Studies at Millbrook, NY. Amynthas agrestis was caught in pitfall traps at high elevations of the southern Appalachians (Callaham et al. 2003). Amynthas agrestis was also collected in Hamilton County, NY (Bernard et al. 2009). The winter temperatures for the Vermont, New York, and Appalachian high-elevation sites are well outside the optimal range for mature A. agrestis determined in mesocosm experiments by Richardson et al. (2009). Yet, climate data and our observations of Amynthas in three locations in Vermont suggest that these earthworms survive and thrive in regions with cold winters (Table 2). 318 Northeastern Naturalist Vol. 19, No. 2 Requirements for the viability of the observed Amynthas populations in Vermont probably include cold-hardy cocoons and short maturation times, from hatching in the spring to maturity in the summer, thus producing cocoons in a single growing season. Since Amynthas are epi-endogeic earthworms, their cocoons are likely exposed to low air temperatures. Protective dehydration (Holmstrup and Westh 1994, Holmstrup et al. 2002) is a mechanism by which cocoons of the common surface-dwelling European earthworm species Dendrobaena octaedra Savigny (Octagonal Tail Worm) remain viable in cold temperatures to -40 °C (Leirikh et al. 2004). Hatching, of course, would occur at much higher temperatures. For A. agrestis, cocoons need to be exposed to temperatures greater than 10 °C before hatching can occur (B. Snyder, Kansas State University, Manhattan, KS, and J. Blackmon IV, Univeristy of Georgia, Athens, GA, pers. comm.). Limitations on the success of Amynthas in Vermont, more northern latitudes, and cold microclimates may also be imposed by the length of their maturation period relative to the local freeze-free period or, considering the findings of Richardson et al. (2009), the contiguous period during which temperatures are greater than 5 °C. Field data collected by Callaham et al. (2003) at Brasstown Bald suggests that the maturation period may be somewhat greater than 50 days. However, their field collection began only in July, and development might have taken place from as early as April when Snyder et al. (2010) found A. agrestis in Great Smoky Mountain National Park (TN). Winter sampling was not conducted because adults and juveniles of A. agrestis are not thought to survive the winter (Snyder et al. 2010). However, adult Amynthas were found under snow at Lake Biwa near Kyoto, Japan (R.J. Blakemore, pers. comm.), which has much warmer air temperatures than those in Vermont (normals at Hikone, Japan, are not below freezing for any month; www.climate-charts.com 2011c), and there are suggestions that some species in the northern US survive into winter as adults (J. Blackmon IV, pers. comm.). However, we were not successful in finding any Table 2. Climate information for locations where Amynthas was found in its original range (Japan) and at sites in Vermont and comparable sites in New York and Georgia. FFD = median frost-free days, T < 0 °C (T < 2 °C); MFD = median (50%) freeze dates, T < 0 °C; Temperature (Temp): min/ max = Monthly normals (low/high), x̅ = mean annual. USDA Temp (°C) Site (NOAA station) Zone FFD MFD Min/max x̅ Reference Quechee, VT (Woodstock) 4b 115 (92) 9/21–5/31 -15/27 6 S. Burlington, VT (Burlington) 4b 147 (129) 0/1–5/20 -13/27 7 Shelburne, VT (Burlington) 4b 147 (129) 10/1–5/20 -13/27 7 Brasstown Bald, GA (Blairsville) 6b 161 (147) 10/10–5/01 -4/29 13 Callaham et al. 2003 Madison County, NY (Morrisville) 6b 134 (104) 9/23–5/24 -10/28 9 Bernard et al. 2009 Millbrook, NY (Millbrook) 5b 142 (116) 10/04–5/08 -10/29 9 Burtelow et al. 1998 Kunashir, Russia (Nemuro, Japan*) 5 148** - -9/17 6 Blakemore 2003 Kii Peninsula (Wakayama, Japan***) 8a/8b - - 2/28 16 Sakai et al. 2006 *http://www.climate-charts.com 2011a. ***http://www.climate-charts.com 2011b. 2012 J.H. Görres and R.D.S. Melnichuk 319 earthworms in 3 to 5 °C soils under 30 cm of snow at South Burlington and Shelburne sites in January or February 2011 (we did not explore the Quechee site). The above-zero soil temperatures under snow pack might still affect hatching phenology as soils may warm up faster in the spring, which may promote earlier hatching and increased earthworm survivorship. The time between median last and first frost dates (days between early and late frost days: T < 0 °C) is 115 days in Woodstock (NOAA station near Quechee) and 161 days in Blairsville (NOAA station near Brasstown Bald), and the time between median early and late dates when temperatures are below 2 °C is 92 days in Woodstock and 147 days in Blairsville (Table 1). The period between late and early dates when temperatures are below 5 °C, the temperature lethal to adult A. agrestis (Richardson et al. 2009), would be even shorter. In Quechee, where we found A. agrestis, the time period conducive for development may be shorter than the maturation period in some years because the freeze-free period of 92 days gives the median number of contiguous days when temperatures are greater than 2 °C. In 50% of years, the freeze-free period is shorter. For Adirondacks (NY) soils, Bernard et al. (2009) showed that acidification and subsequent base cation depletion is probably hindering Amynthas invasion and thus accounting for their absence. However, an alternative explanation may be that temperature regime limits these worms from colonizing the Adirondacks. For the four NOAA stations located in the Adirondacks, the freeze-free period (period between median early and late freeze dates at a threshold temperature of 2 °C) are less than a hundred days. The freeze-free period is 70 days at Old Forge, NY, 81 days At Newcomb and Indian Lake, NY, and 76 days at Big Moose, NY, all periods considerably shorter than those at the other New York or Vermont stations. Based on Adirondacks and Vermont freeze-free periods, we suggest that the maturation period is somewhere between 80 (longest freeze-free period in locations without Amynthas) and 92 days (shortest freeze-free period in locations with Amynthas). The freeze-free period may be an important factor limiting the presence and abundance of Amynthas in Vermont, but moisture may also affect their abundance (Richardson 2009). Itt is unlikely, however, that moisture limits Amynthas in Vermont during an average year, as rainfall in April through November averaged greater than 75 mm per month precipitation for the climate period from 1971 to 2000 (USDC-NOAA 2007). However, drought events may limit the abundance of these earthworms and confine them to moist soils, as observed in the Appalachians (Snyder et al. 2010). Global climate change is often predicted to cause an expansion of the range of invasive species. However, the fate of Amynthas is uncertain and would depend on at least four hitherto unknown life-history traits: cold-hardiness of the cocoons and adults, hatching phenology, and the length of the maturation period. It is not clear how winter warming would affect soil temperatures. The lengthening of the freeze-free period in Vermont (Skinner et al. 2010) may result in less snow cover, paradoxically resulting in colder, below-freezing soil temperatures more often (Decker et al. 2003, Groffman et al. 2001). We speculate that this effect may 320 Northeastern Naturalist Vol. 19, No. 2 negatively affect Amynthas abundance, but we suspect that, given the wide range of climates that Amynthas straddle, earthworms of this genus will likely become long-term inhabitants of Vermont forests. Acknowledgments We like to thank Dr. R.J. 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