Main: (Geometridae / Larentiinae)
70.1271 [B&F: N/A] Cryptic Fern (Horisme radicaria) (La Harpe, 1855)


Very closely related to the more common and widespread Fern H. tersata, H. radicaria was added to the British list from a specimen taken in East Sussex on 22 May 2019, and a number more from East Sussex and Kent in 2020 indicate that it is now resident locally in those two counties; retrospective records from East Sussex in 1990 and Kent in 2004 and 2007 make it probable that it has been present for a number of years. The species does appear to have experienced and north and westward range expansion on the near continent, so its arrival may be relatively recent. See Clancy and Smith in Atropos: 66 for more details.

Adults should be photographed and retained for dissection, as distinguishing features between radicaria and tersata are subtle, especially if the moth is worn. The above quoted article has full details, but in summary radicaria has a longer, more defined apical streak, stronger cross-lines and darker forewing tone. Like its congener, the larval foodplant is Traveller's-joy Clematis vitalba. Both species are double-brooded in Britain, found between May and early September.
Status update: 27/08/2020

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