Use of a marsh dominated by the introduced European Lake Sedge, <em>Carex acutiformis</em>, by highly localized native butterflies

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To determine whether native butterflies had colonized a marsh in Ottawa that was entirely dominated by the invasive alien European Lake Sedge (Carex acutiformis), we surveyed two adjacent stands of the sedge and surrounding habitats. Dion Skipper (Euphyes dion), Mulberry Wing (Poanes massasoit), Broad-winged Skipper (P. viator), and browns (Lethe spp.) were all abundant in the introduced sedge, but absent from surrounding habitats. This is the first report of the use of invasive-dominated wetland by native Canadian butterflies. Reduced nectar resources because of dominance of the invasive species over native nectar-producing plants did not prevent significant colonization. The known restriction of the butterflies to native Lakebank Sedge (Carex lacustris) as a larval host plant, but its absence in the area, coupled with dominance of its close relative, European Lake Sedge, provides strong circumstantial evidence of the use of the latter as larval food. This report doubles the number of recently localized native butterflies that have been able to increase their distribution by switching to habitat dominated by invasive plants.