Ophiogomphus anomalus Harvey, 1898
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Basis for Listing
Ophiogomphus is primarily a Holarctic genus, with the greatest diversity of species being in North America. The Extra-striped Snaketail (Ophiogomphus anomalus) has an eastern Nearctic distribution and is found in the Great Lakes, New England, and maritime regions, from Nova Scotia and Maine, south to Pennsylvania and New Jersey, and west to Wisconsin and northeastern Minnesota. Adjacent to Minnesota, it has been found in west central Wisconsin at sites along the Chippewa, Flambeau, and St. Croix rivers, and it has also been reported from the Gull River in the Thunder Bay region of Ontario. There are 150-200 known occurrences of this species reported in the United States and Canada (NatureServe 2015). Although this species has been found in abundance at a few sites, it is highly localized throughout its fairly limited range and is usually reported in small numbers when found.
Despite targeted searches in Minnesota (Montz 1993; Steffens and Smith 1999; Steffens 2001, 2004), the Extra-striped Snaketail has only been found in the Pigeon and Brule rivers in Cook County and in the upper St. Louis River in St. Louis County. The species has been located at several sites along the St. Croix River in Wisconsin but, to date, the species has not been recorded on the Minnesota side of the river. Given its limited distribution, the Extra-striped Snaketail was listed as a special concern species in Minnesota in 1996.
The Extra-striped Snaketail has been listed as an endangered species in Wisconsin since 1989.
The Extra-striped Snaketail is a medium-sized, bright green and black dragonfly, with a cobra-like clubtail. The adult has a medium-sized body that is approximately 4.3 cm (1.7 in.) long. This species has widely separated eyes; narrow, black, facial stripes, and a bright green thorax on which black, interrupted, lateral stripes form an “N” shape. The abdomen is black, with yellow, dorsal spots; segments S1-S7 have yellow, triangular, dorsal spots; segments S8-S9 are rounded. The female has upright, occipital horns and small, postocular horns.
Larvae of this species are slightly flattened dorso-ventrally, and their abdomen is oval, with a cylindrical, wedge shape. Their wing cases are divergent, and their antennae are thickened at the fourth segment, which differs from other related species. The Extra-striped Snaketail’s tibiae are short and twisted, with hooks for burrowing into substrate.
In Minnesota, this species is a resident of the Border Lakes and Northern Superior Uplands subsections adjacent to rivers draining into the Lake Superior watershed. The main breeding populations have been found at several locations in Cook County (Montz 1993). In addition, Steffens (2000) reported an occurrence near Pineville in St. Louis County (Tamarack Lowlands).
In general, Ophiogomphid larvae prefer clear, swift flowing rivers. Adults patrol these rivers and forage in adjacent wetlands, lowland forests, and mature upland forests with closed canopy and low understory. They tend to disappear from cleared or cultivated regions due to the reduction of sheltered shoreline vegetation for adults as well as changes in flow and siltation in the larval habitat.
The Extra-striped Snaketail is usually found in and along small- to medium-sized rivers that have rapids and riffles and are up to 1 m (3.3 ft.) deep, with a substrate of gravel, sand, and cobble. Preferred water temperature ranges from cool to warm. The preferred, terrestrial vegetation in adjacent areas seems to be mature mixed-hardwood forest with minimal fragmentation and a large, continuous, riparian buffer zone.
In Minnesota, the sites where the Extra-striped Snaketail has been found are characterized by pristine, medium-sized rivers with rapid current, high oxygen content, and high water quality. Many, spring-fed streams drain the landscape, which is moderately low to hilly. The watersheds have extensive forest coverage, usually undisturbed old growth or mature second-growth mixed forest of aspen (Populus spp.), birch (Betula spp.), and conifers (Northern Fire-Dependent Forest), or birch, maple (Acer spp.), and pine (Pinus spp.) (Northern Mixed Mesic Hardwood Forest). These areas are largely managed as state or national forest or are managed by the National Park Service and are in regions of low population density (10 or fewer people per square mile).
Biology / Life History
The larval ophiogomphid diet generally consists of other insect larvae such as midge and mayfly nymphs. Adult ophiogomphids usually forage for other flying insects that are approximately their size or smaller. They hunt away from the water’s edge, in adjacent forest areas and can be seen flying up to tree top level in the canopy in search of food.
Extra-striped Snaketail larvae may be locally abundant in selected sites, however, smaller numbers of adults have been observed at those same sites. This suggests that there may be a high mortality at emergence. While adults are not known to be territorial, they have been observed patrolling regular beats along streams when searching for a mate. Although they forage for food in woodland areas, they often remain within 30 m (98 ft.) of the shoreline from which they emerged. They perch or rest in treetops in evening and early morning.
Ophiogomphids generally have a 2-year life cycle, wherein the larvae overwinter and then emerge as adults the following summer. Males patrol rivers and usually mate while perched on bushes and trees along the shoreline. Females oviposit alone by irregularly tapping their abdomen into the river, dispersing their eggs directly into the current. After hatching, larvae burrow into the sandy substrate of the river bottom. At maturity, larvae emerge from water in midmorning and crawl away from shoreline for some distance. Over the course of several hours, they undergo transformation while resting on rocks, vegetation, or even high up on the trunks of large trees. Emergence of the Extra-striped Snaketail has been observed in May or early June, with the flight season extending into early August.
Conservation / Management
Steffens (2000) reports that this species is typically found in areas where the watershed has a forest cover of 70% or more. In addition, natural resource maps indicate that known occurrences of this species coincide with remote, minimally fragmented, riverine forest habitat (LMIC 2002). Appropriate conservation measures for this species include maintaining wide, riparian forest buffer zones and preventing fragmentation of the larger forest areas in watersheds where this species is found. Shoreline land clearing increases runoff and sedimentation that can have a negative impact on the larvae, which depend on cool, clear water that is free of siltation. Additionally, chemical and organic pollution from agricultural, municipal, and industrial sources may compromise water quality beyond the tolerance of this sensitive species. Shoreline clearing may also negatively impact adults of this species, which seem to require forested, riparian areas and nearby forested wetlands for their feeding and reproductive activities. The spread of zebra mussel (Dreissena polymorpha) populations in the Lake Superior basin may also negatively impact this species, as there have been reports of other gomphid populations being impacted by this nonnative, invasive species (Tucker and Camerer 1994).
As this species prefers high quality streams within undisturbed riparian forest zones, the lack of adequate dispersal corridors may become a concern if pollution, land clearing activities, or even climate change impact their current habitats.
Conservation Efforts in Minnesota
Survey work at the sites where Extra-striped Snaketails have been reported has been done primarily by Steffens and Smith (1999, 2000) and Montz (1993). While dragonflies have been surveyed by other researchers in many other parts of Minnesota, the Extra-striped Snaketail has been found at only a small number of sites. Based on similarities to habitat characteristics at known sites, expanded survey work along the main streams and drainages of the Big Fork and the Little Fork rivers of north-central Minnesota, the Vermillion River of northeastern Minnesota, and the upper St. Louis River is recommended.
The non-profit Minnesota Dragonfly Society is looking for Zigzag Darners (among many other species) throughout Minnesota through surveys and educational workshops. These surveys are conducted by volunteers and are supported through an Enbridge Ecofootprint Grant through 2018.
Kurt Mead, MN DNR, 2017
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