Natural Causes

A dead Four-spotted Skimmer was found on our driveway this afternoon. Mysteriously, the dragonfly held a rather life-like pose. It looked as though it had died while perched, dried in that position, and then fell to the ground, dislodged perhaps by a gust of wind. This brought to mind an old question: How often do dragonflies die of old age? I've wondered about this off and on. Many adult dragonflies, at least in the northern latitudes, live long enough to succumb to the frosts and freezes of autumn and avoid predation that way. Still, a death by natural causes and not a death caused by nature (i.e. bats, birds, frogs, fish and other dragonflies) seems to be a rarity. In fact I know of only one eye-witness account. Ken Tennessen, fellow odonatologist and poet, once told me of a time he was watching a dragonfly and it just quietly fell from its perch, dead. "It has to happen on occasion," he added, after a quiet philosophical pause.

Publicado por scottking scottking, 07 de julho de 2017, 12:22 PM

Observações

Fotos / Sons

What

Libélula de Quatro Pintas (Libellula quadrimaculata)

Observador

scottking

Data

Julho 6, 2017 05:23 PM CDT

Descrição

Four-spotted Skimmer
found dead in driveway
Northfield, Minnesota

Fotos / Sons

Observador

scottking

Data

Julho 6, 2017 05:07 PM CDT

Descrição

Jewel Beetle (No. 14)
captured from Cerceris fumipennis
Cowling Arboretum
Northfield, Minnesota
TL=12mm

Fotos / Sons

Observador

scottking

Data

Julho 6, 2017 05:07 PM CDT

Descrição

Jewel Beetle (No. 13)
captured from Cerceris fumipennis
Cowling Arboretum
Northfield, Minnesota
TL=12mm

Fotos / Sons

Observador

scottking

Data

Julho 6, 2017 05:03 PM CDT

Descrição

Jewel Beetles
captured from Cerceris fumipennis
Cowling Arboretum
Northfield, Minnesota

Fotos / Sons

Observador

scottking

Data

Julho 6, 2017 02:35 PM CDT

Descrição

Square-headed Wasps, male and female
with fly
Cowling Arboretum
Northfield, Minnesota

Fotos / Sons

Observador

scottking

Data

Julho 6, 2017 02:12 PM CDT

Descrição

Sanborn's Beewolf, male
Cowling Arboretum
Northfield, Minnesota

Fotos / Sons

Observador

scottking

Data

Julho 6, 2017 01:41 PM CDT

Descrição

Ant Queen Kidnapping Wasp
with ant
Cowling Arboretum
Northfield, Minnesota

Comentários

Interesting comments, Scott. I have occasionally found a dead dragonfly with no apparent injuries that was away from a street or roadway that I just assumed had died naturally, but I've never just seen one die such as Ken's experience. But like you, I would think the vast majority end up as prey or killed by cars, etc.

Publicado por greglasley mais de 4 anos antes (Sinalizar)

Greg, thanks for mentioning cars. I overlooked that. A large cause of mortality for meadowhawk eggs is habitat alteration. Each year adults mistake mowed lawns and trails as dried temporary ponds, the short grass to tall grass transition at lawn edge and trail edge resembling a small dried pond. All the eggs mistakenly deposited in these areas have no chance of survival.

Publicado por scottking mais de 4 anos antes (Sinalizar)

Here in Texas, Wandering Gliders can be seen depositing eggs on shiny car hoods while you sit in traffic at a red light on a hot summer day. Fried eggs for sure!

Publicado por greglasley mais de 4 anos antes (Sinalizar)

I have never seen one die naturally as Ken's account, but I have found some very mature-looking specimens that I believe likely just ran out of time. Occasionally I'll find corpses of obviously mature dragonflies with various decomposers doing their thing, but it's possible a bird or asilid ended the dragonfly's life and dropped them.

Often I think about what both of you mentioned, essentially "false positives" in habitat selection as a result of urban ecology. Even examples such as possible increased predator success rate due heightened visibility of Libellula croceipennis seen on a car antenna. Each year I watch Epitheca petechialis and some other species patrol and occasionally oviposit in residential swimming pools.

I'm sure we could each think of other examples and plenty of examples outside the realm of dragonflies. Anyway, it's interesting to think about. Modern urban/suburban environments have been around such a short time in relation to insect selection and evolution (and will possibly just be a blip on the radar) but they essentially throw a wrench in eons of practical selection.

Anomalous situations have altered and wiped out lineages in the past so in a sense the false positives in humanized environments isn't really new. One species thrives (or destroys habitats, builds needlessly large houses, contaminates water sources, etc.) at the expense of others. I guess the difference is these are conscious modifications rather than instinctual.

Publicado por briangooding mais de 4 anos antes (Sinalizar)

The loss of habitat and large-scale alteration of landscape due to us humans seems unparalleled. I'm not too optimistic about the consequences. It's true anguish, ineliminable suffering, to know we are such a threat to nature and yet seem so incapable of stopping ourselves. With projects like iNaturalist it's easier to see what diversity and richness we stand to lose.

Publicado por scottking mais de 4 anos antes (Sinalizar)

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