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including myself. Subsequent searches in 1984
have revealed further Essex sites, and the status
of dryas as a breeding species in Essex seems
secure once more.
Probably the main value of mapping the distribution
of animals or plants is to get some idea of the
effects of climatic and land-use changes on the
other living species with which we share this
planet. Dragonflies, because they are predators,
and spend different parts of their lives under
water and on land, are extremely good indicators
of the quality of the environment. Conservation
policies adapted to the welfare of dragonflies
could be expected to benefit a wide range of
other plant and animal species as well. Some
of the most suggestive evidence coming to light
in the present dragonfly survey is what one
observer, Dave Martin, called a 'dragonfly
desert' in the north west of the county.
Intensive arable agriculture, with loss or in-
filling of farm ponds and other open water, and
pollution of what remains by fertiliser run-off
creates a very hostile environment for dragon-
flies. Interestingly, the few remaining sites
which look favourable to dragonflies still
appear to support very few species (for
example, Aeshna grandis and Ischnura elegans,
our two most tolerant species). One possible
explanation for this is that the often quite
considerable distances, without favourable
intermediate habitat, which separate suitable
habitats obstructs dispersal of species to
occupy adequate breeding sites, even when these
exist. Another consideration is that chalk and
chalky boulder clay are the main soils in the
north west. Aquatic habitats would therefore
tend to be calcareous, another factor telling
against a rich dragonfly fauna.
Also important from the point of view of