8
THE ESSEX NATURALIST
been found. Bats have been observed only between the middle
of November and early March, and usually in an inactive state,
so it is presumed that the holes are used only for hibernation.
However, the hibernating colony would appear to be small; the
greatest number of bats seen on any one visit being about 20.
Some bats have been examined for ectoparasites and about 25
have been marked with metal rings fixed on the right fore-arm.
So far none of the marked bats have been recovered.
Ectoparasites have included the interesting bat fly, Nycteribia
(Listropoda) latreillei Leach, the flea Ischnopsyllus simplex
Rothschild, N. C, being the first record of this species from Essex,
George (1959), and many mites, which have not been identified,
from both Daubenton's and Natterer's Bats.
Remains of dogs, hedgehogs and mice have been found from
time to time. Living mice (species ?) have been seen, but these
were presumably accidental visitors, and probably would not have
survived very long. Mouse traps set in various holes in May 1959
produced no captures, and we have seen no mice since that date.
Invertebrate Fauna
While having many characteristics in common with natural
underground environments, the deneholes differ in some important
ways, viz:
(i) The walls, floor, and roof of the chambers consist of tightly
packed chalk with no significant cracks. Many of the floors have
little soil covering and no pools of water are present.
(ii) The only means of entry, or exit, is by means of the vertical
shafts.
(iii) The influence of human agencies is considerable and
diverse. The effect of numbers of visitors leaving behind organic
and inorganic material, and spreading microflora and possibly
some small animals to the chambers remote from the open shaft,
to mention only two activities, must be great.
Purposeful and accidental introduction of material down the
shaft is of importance to the animals living on the heaps of debris
at the base, and is probably significant in the food-cycles of the
holes in general.
From (i) above it would be expected that a rather poor truly
Cavernicolous fauna would be found. With regard to (ii), it is
difficult to imagine a potential troglophile being attracted to the
well-illuminated opening of the shaft, and thus entering the suit-
able environment by falling down. Entry to the holes must be
in the main accidental; the range of species and proportions of
the species being governed by their occurrence within a small
area of ground around the top of the open shaft. These comments
may not necessarily apply to flying insects.