A Common Resource - Gower - page 210

FIG 115. Mating hornet robber flies. The robber fly is a conspicuous element of the dung community. (David Paint-
er)
Another rare member of the dung community that definitely has an association with dor beetle larvae,
being a parasite in their burrows, is the beetle Aphodius porcus , which has been recorded from Fairwood
Common.Thoughmostdungbeetlesareveryactiveincollectingdung,afewsuchas Aphodius areknown
as'cuckooparasites'becausetheyeatandlaytheireggsondunganotherbeetlehascollected,ofteneating
that beetle's eggs as well as appropriating their dung.
The increasing use of persistent parasite treatments for cattle, such as avermectins, is thought to be
having an effect on species such as the robber fly as they kill its hosts in the cowpat, although more re-
search is needed. These treatments, first developed in the 1980s, are given to grazing animals to remove
gastrointestinal parasites, mainly nematodes, but unfortunately they have other side effects. It has been
found for example that insects feeding on dung containing avermectins are either rendered infertile or
producemalformedlarvaeincapableofdevelopment.Asaresultthedroppingsoftreatedanimalsdegrade
muchmoreslowlythanwouldotherwisebethecase.Therearealsosuggestionsthattracesofavermectins
in dung may make it more attractive to dung beetles. If this is the case then there are serious long-term
problems both for this vital insect community and for many other species that feed upon them. There are
currently no restrictions on the use of avermectins by farmers in the Tir Cymen or Tir Gofal agri-envir-
onment schemes; there is a presumption against their use on SSSIS and Wildlife Trust reserves where the
robber fly occurs, but these areas are in practice not always free of avermectins.
Theinsectsandespeciallybeetlesassociatedwithdungformanimportantpartofthedietofthelarger
bats, such as the horseshoe bats for which Gower is a stronghold, mainly during the late summer and au-
tumn when the young are laying down fat reserves prior to hibernation. Greater horseshoe Rhinolophus
ferrumequinum , lesser horseshoe R. hipposideros and serotine bats Eptesicus serotinus rely heavily on
beetles in the autumn and possibly the winter. It is a common misconception that bats hibernate continu-
ously throughout the winter months. All species wake up at fairly frequent intervals. The temperatures
they require change through the winter and the bats will move to new overwintering sites if necessary.
They often travel many miles, and if the weather is mild enough they will also feed. Horseshoe bats in
particular wake up very frequently and may feed throughout the winter - and even in February they feed
on dor beetles. Nearly half of the diet of lesser horseshoe bats during the winter consists of dung flies.
If this winter source of food was denied them through the widespread use of avermectins, the bat pop-
ulations of Gower could be seriously affected. The extraordinary adaptation of the dung mosses to use
dung flies to disperse their spores also makes them potentially vulnerable to the use of these chemicals.
Alternative methods of treating intestinal parasites need to be developed. Recent studies on the effects of
avermectins suggest that this is an issue that needs to be urgently addressed.
PLANT AND ANIMAL COMMUNITIES
Despite potential problems with parasite treatments this constant grazing is vital in maintaining both the
open character of the commons and the rich variety of wildlife. The abundant oak seedlings found on
manyofthecommonsindicatethat,despitecenturiesofgrazing,theseareaswouldrapidlyreverttowood-
land if the use of common rights ceased. Lightly grazed areas such as Barlands and Clyne commons, for
example, are now becoming overgrown. Not only does the removal of vegetation by grazing animals in-
fluence the succession of vegetation, but the physical effects of trampling and grazing also play an im-
portantroleincreatingimportantmicrohabitatsformanyspecies.Grazingalsocreatesavariedvegetation
structure, increases the diversity of plant species and reduces competition from dominant species. In par-