The dragonflies are considered to be good bio-indicators of water quality, but which of them are the best to use?also which is the better to use – dragonfly or damselfly…
Dragonflies tend to be more sensitive to pollution than damselflies, but depending on the species it can depend on a wide array of environmental conditions where they will flourish or perish. It may determine on where you are located specifically, but according to a 2005 study done by Paul Catling in sewage ponds in Ontario and published in The Canadian Field-Naturalist, it may be age of your dragonflies or damselflies that is more important, as “Nymphs in early spring may provide the best indication of water quality die to direct association with water following a period of stress” (235). Yet, “adults appear to be able to recognize water quality and some species tend to occur only on the cleaner ponds” (235). I would suggest taking a look at the entire article in PDF form, which can be found online at this link:
Differences between dragonflies and damselflies are centrally morphological, in that their wings differ–dragons flies do not have hinges that allow them to fold their wings together when resting, while damselflies do. Other things to consider when deciding to use damselflies or dragonflies are that food shortages limit reproductive behavior, so make sure your location is rife with small insects, especially flies, ants, etc. Also, dragonflies do not hunt in cold weather, but damselflies are not as effected by temperature. Yet, dragonflies are more powerful fliers.
You will also have to consider selecting a species that is either widespread in its population or highly local. Some families only live in cool streams or rivers, others in ponds or clear water, and some only in marshy places. Some species can toleratre poor water quality and low oxygen levels. Overall, “the acidity of the water, the amount and type of aquatic vegetation, the temperature, and whether the water is stationary or flowing” (Berkeley) all affect if a population will be sucessful or not.
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