Marpissa grata (Gertsch, 1936)
A Jumping Spider
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Hyctia grata, Marpissa wallacei
Basis for Former Listing
Marpissa grata (a species of jumping spider) is a Great Lakes endemic known only from Michigan and Minnesota. It was originally collected by Gertsch (1936) in Minneapolis, Minnesota, and is known from five counties. This suggests that the Minnesota populations may be significant to the conservation of this species nationally. Marpissa grata was listed as a special concern species in Minnesota in 1996. Special concern jumping spiders are those known from three or more sites in Minnesota but with significant range restrictions or particular habitat associations that make their populations appear vulnerable from a conservation standpoint.
Basis for Delisting
Since its listing as a special concern species, M. grata has been documented at eight new sites in six additional counties distributed widely across the state. These data suggest that this species is more common and widely distributed in Minnesota than was formerly believed. Marpissa grata was delisted in 2103.
Jumping spiders are one of the most recognizable spiders as they generally have a stout body, rather short legs, a very large set of eyes, and the ability to jump. Their body shapes and colors often imitate prey such as ants and beetles. Marpissa grata has a very elongate abdomen and is dark brown in color with central yellow patches. The similar M. pikei has been associated with more xeric habitats and has faint spots on a light background in irregular lines along the length of the abdomen.
Marpissa grata prefers habitat that contains sedges or emergent vegetation. Most, but not all, records are associated with wetlands, ponds, or rivers. All specimens collected by Ehmann and Boyd in 1996 were near cattail (Typha spp.) marshes on cattails and willows (Salix spp.). However, several specimens collected in 2004 in Otter Tail County were from a drier site dominated by big bluestem (Andropogon gerardii). Cutler (1971) linked this species to bluegrass (Poa pratensis) meadows, and this association has held true at Lake Elmo Park Reserve in Washington County (Ehmann and Boyd 1997).
Biology / Life History
Jumping spiders do not spin webs for catching prey. Instead, they construct small tent-like silken retreats under rocks or logs or on plants, which they use at night and during hibernation. The females also lay their eggs in them. Jumping spiders are most active during the day, and they prefer sunshine. They tend to stay in their retreats on cloudy or rainy days. Jumping spiders are generally interested in whatever approaches them and will often turn and face human observers and may even advance towards them. They are generally harmless to people.
Conservation / Management
The best time of year to survey for M. grata is from June through September. Future surveys may want to employ alternative sampling techniques to sweep netting such as hand searches and leaf litter collection. Although remnants of natural areas may often be too small or isolated for some rare vertebrates, they may be suitable for maintaining invertebrates. Each new locality for a species adds to the suite of management options for their conservation and may even guide new land designations or acquisitions. Benign to humans, diverse, colorful, and behaviorally complex, jumping spiders may be good ambassadors for their kin and invertebrates in general.
Conservation Efforts in Minnesota
In 1996, Ehmann and Boyd (1997) confirmed the presence of M. grata in Stearns County (previously reported by Cutler ) and within Washington County at a new locality. Significantly, M. grata was also discovered in Murray County in 1996 and in Jackson County in 2007, which extended the range limit of this species more than 200 km (124 mi.) southwest. A single adult specimen was collected in Sherburne County for the first time in 2001 (Ehmann 2002), and in 2004 several adult and immature specimens were collected at two sites in Otter Tail County. The absence of M. grata in apparently suitable habitat elsewhere in the state combined with extremely low collection numbers from sites where it is found is consistent with the interpretation that this species is rare in Minnesota. Any new records will be of high interest.
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