Friday, 25 October 2013

Life in the Freezer

Another interesting question from Johnnykinson asking if I know the lowest temperature at which a dragonfly can survive.
The quick answer is no but that hardly constitutes an interesting post to keep my reader(s) happy ;) so a bit of research was necessary to go with my basic general knowledge.

It's a fact that dragonfly species inhabit every continent but the Antarctic, and it's generally accepted that all around the world the arctic treeline is the most northerly latitude for dragonflies to thrive.

Looking at distribution maps for Europe, the range of some species extends to northern Scandinavia (Common Hawker and White-faced Darter for instance) and there are others which are sub-arctic specialists and only found in the north like Azure Hawker and Northern Emerald, indeed the scientific name for northern emerald (Somatochlora arctica) actually translates as 'Green-bodied of the Arctic'.

Only one European species, the Treeline Emerald (Somatochlora sahlbergi) is found exclusively in remote regions north of the arctic circle, surviving also the inhospitable climates of Alaska, north-west Canada and Siberia, overcoming the remoteness of the habitat, poor weather conditions and a very short summer.

They survive in small, deep ponds and lakes of the arctic tundra, mainly woody heathlands with a scattering of small birch and pine trees. The fact that average adult lifespans are no more than 6-8 weeks in most species of our region means the summer season doesn't have to be that long, but habitat would also have to contain a decent amount of prey species to ensure survival of the adult dragonfly (same reason birds migrate and bats etc hibernate).
Obviously the ponds themselves would have to contain food species too, and as most of their lives are spent underwater, a lot depends on the hardiness of the larva to survive the winter months. Experiments have actually taken place which have proven that all but the smallest of larval stages can survive being frozen (to about -5c) and thawed out again so that shouldn't present too much of a problem if the water is deep enough to avoid freezing altogether.

So no definitive answer I'm afraid as far as actual temperatures are concerned for the adults. Being cold-blooded anyway they have their own inbuilt temperature regulators, (wing-shivering being the most obvious) but as long as food is available and enough short periods of warmth exist for the adults to be active, dragonflies of one species or another will survive all but the most desolate of climates. It always amazes me anyway that after a few days of cold wind and rain (like recently) a bit of sunshine sees them out in numbers again, even in October (see last post).   

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