It is not known how they got there, neither species was recorded by Lousley in his 1971 Flora, although spores from ferns can be blown some distance; Chilean hard-fern was recorded in Higher Town, St Martin's in 1936.

There, a few Douglas firs two to three centuries old escaped clearcutting in the 20's, and the understory is told by luxuriant bracken and sword and deer ferns.

The first stage larvae feed on various Ferns, including Dryopteris, Blechnum spicant and Pteridium aquilinum.

A fern called the "deer fern" or "hard fern", Blechnum spicant, grows near Deildartunguhver.

Fern collections include Adiantum pedatum, Asplenium scolopendrium, Athyrium filix-femina, Blechnum spicant, Dryopteris affinis, Gymnocarpium robertianum, Matteuccia struthiopteris, Phegopteris connectilis, Phyllitis scolopendrium, and Woodsia obtusa.

These contain bluebell Hyacinthinoides non-scripta, bilberry Vaccinium myrtillus, the hard fern Blechnum spicant and honeysuckle Lonicera periclymenum with birds-nest orchid Neottia nidus-avis and violet helleborine Epipactis purpurata found particularly under beech.