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Dragonflies
at La
Cassinazza
ILLUSTRATED CHECKLIST
Dragonflies are biologically complex insects
with a unique lifecycle
tied to aquatic habitats. Their larvae live underwater until the time
they
transform into adults, which are wonderfully adapted to an aerial
lifestyle; in
both of these stages they are predators, feeding on other invertebrates.
During the various stages of their lives, they have specific ecological
needs:
uncontaminated waters with aquatic plants and an abundance of other
insects for
egg-laying and for the development of larvae; adults on the other hand
require
rich and varied riverside vegetation.
Dragonflies are thus an important biological indicator of environmental
quality.
In the Po Plain, most species have undergone a drastic population
decline in
the last twenty years; some have become rare, while others have
practically
vanished.
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There
are only limited areas of fast-flowing, clear, and well-oxygenated
waters at La
Cassinazza; these are
favoured by species such as Calopteryx splendens.
Slow
or stagnant waters, colonised by aquatic plants and surrounded by dense
waterside vegetation, are a species-rich habitat, the most abundant of
which at La
Cassinazza
include Ischnura elegans, Platycnemis
pennipes, Crocothemis
erythraea, Aeshna cyanea.
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Dragonfly
studies at La Cassinazza
began in 2000, under the initiative of Prof. Groppali of the University
of Pavia;
field studies were conducted by Elisa Riservato, who sampled
dragonflies in
certain habitats (1). Elisa continued collecting data in 2001 as well,
which
became the subject of her undergraduate thesis (2).
Subsequently,
records were gathered in a non-systematic manner, relying only on
visual
observations (either with the naked eye or with binoculars, and often
supported
by photographic documentation), which makes it possible to identify
almost all
the species seen, with the exception of a few instances of dragonflies
observed
only in flight and belonging to difficult species groups.
Dragonflies
begin to make their appearance at La Cassinazza
once spring is well underway, with the
first individuals typically seen at the end of April.
As the summer heat begins, dragonflies become a constant, diverse
presence;
species diversity peaks in mid-summer, with 15/16 species in the months
of July
and August. Diversity remains high through September, but drops rapidly
after
that, with the last observations coming in early November.
Thanks
to countless hours of observation and the many photographs taken, we
have
prepared an illustrated checklist of
all
the dragonfly species that have been recorded at La Cassinazza.
The
data gathered during the first five years of record keeping was
presented at
the conference on Dragonfiles
in Italy:
Research and Conservation, which took place in February 2007,
with a
presentation titled: Evolution and
phenology of a dragonfly community in a re-naturalised area.
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