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Study of Common Fan-foot (Pechipogo strigilata) in Wyre Forest
© Rosemary Winnall
Larvae
Larval hunts sounded likely to be near impossible, with accepted knowledge suggesting that they would be high up in the mature oak canopy and then falling to the ground in autumn. Searching the canopy would be impossible and therefore the only hope was thought to be searches of oak leaf litter by sieving / vacuuming leaves etc! To improve chances of locating larvae in leaf litter I decided to use a GPS (Garmin GPS12, recommended for use in well-wooded sites) to record exact trap locations where maximum numbers of flying adults were found in spring and then to return in autumn / winter and check through all leaf-litter within say a 10 metre radius (even this seemed near impossible!). Also felled oaks with leaves on were to be checked.
B. Skinner (pers. comm.) also mentioned that larvae of the closely related Olive Crescent (Trisateles ematualis) had been located by branch snapping in spring. This technique was tested by snapping oak branches at approximately head height (each branch about 1 metre long with at least 1 bunch of leaves on it), and branches were left hanging from the tree, still attached, to allow leaf wilt in time for females to lay eggs on them.
It was decided to try this technique and between 19th May 2002 and 8th June 2002 about 20 branches were snapped. These were to yield good numbers of larvae later in the season. A further 6 branches were snapped on 21/6/02, but these branches yielded no larvae and didn’t curl the ‘right way’ – snapped too late in season, even though moths were still flying in good numbers and this being good habitat.
Larval hunts were carried out from 1st August to 30th September, looking at leaf-litter and oak branches on the ground, snapped hanging branches as above, plus other bunches of dead leaves hanging from oak trees and within reach. Dead leaves of birch, hazel (Corylus avelana), beech (Fagus sylvatica), and bramble (Rubus spp.) were also checked. This consisted of careful checking of all leaves for all larvae and signs of feeding on bunches of leaves. In time, leaf searches could be narrowed down to just the longitudinally rolled leaves that had wilted in a characteristic way, these being the only ones that yielded larvae.
During the search period 65 larvae at various instars were discovered. Many more than was originally thought possible!
Experience in the wild, in spite of checking quite a number of suitably wilted leaves, has yielded no larvae on any species of leaf apart from oak, the only exception was a single larva on birch leaves in oak understorey. Beech, alder, hazel, birch and bramble were all been checked. In captivity larvae were choice-tested in containers with a choice of oak and one other species. When placed on the other species of leaf they were found to partially eat the alternative leaf before moving to the oak leaf within 24 hours. This was true for hazel and bramble, while bracken (Pteridium aquilinum) and birch were not eaten at all.