A Dragonfly Apart

Explanation: Forget searching for the Black Petaltail (Tanypteryx hageni) dragonfly at your local pond, marsh or stream.

This species only occurs in two very specialized habitat types in the Pacific Northwest, USA: hillside seep meadows with sheet water flowing over the surface, and bogs featuring Darlingtonia californica, the California Pitcher Plant or Cobra Lily.

There are distinct advantages and disadvantages to the Black Petaltail's occurrence in uncommon, local and specialized habitats like hillside seeps and bogs. On the plus side, other dragonfly species are rare or absent at these sites, so competition for resources is much less than at ponds or marshes. The risk of predation from birds like swallows and blackbirds is also greatly reduced, as bogs and seeps do not provide suitable breeding habitat for these birds. Life is relatively safe and easy for an adult Black Petaltail compared to most other dragonflies.

This is perhaps one reason why the Black Petaltail is one of the "tamest" dragonfly species and is quite fond of perching on people ... including on my own pants leg, as in this next photo:

The tradeoffs for selecting this type of habitat, however, are considerable. These seeps and bogs are usually small in size, surrounded by forest, and typically occur at higher elevations in the mountains. Therefore, it takes a long time for these insects to warm up each morning, which limits their daily activity period -- including feeding and breeding -- to usually just a few hours in the late-morning and afternoon.

Typical habitat of Black Petaltails -- a wet meadow bog in the high country of
the Cascade Mountains of central Washington state, USA.

The total amount of suitable Black Petaltail habitat is limited and patchy, and therefore these dragonflies occur in low population densities, with populations often widely scattered over the landscape. This makes them more vulnerable to disturbances such as drought and wildfires, and when local populations are extirpated it may take a long time for these sites to become re-colonized.

Black Petaltail adult on perch in the sun.

The petaltail larvae, which are terrestrial and live in burrows in the moss and mud, have a short summer season to develop, so they typically spend an amazingly long five years in the larval state before they transform into adults, much longer than most other dragonflies.

The larval habit of feeding on terrestrial prey can be considered both a "pro," due to the total avoidance of competition with other odonates (i.e. dragonflies and damselfies), and a "con," because they now compete with terrestrial species and are subject to predation by species like mice and shrews, and possibly spiders or beetles (D. Paulson, personal communication).

Time will tell if the Black Petaltail will survive in its specialized niche or, if like many other specialist species, the "cons" of their narrow niche eventually outweigh the "pros."

Information:

Corbet, Philip S. 1999. Dragonflies: Behavior and ecology of Odonata. Cornell University Press, Ithaca, New York. 829 pp.

Kerst, C., and S. Gordon. 2011. Dragonflies and damselflies of Oregon: A field guide. Oregon State University Press, Corvallis. 304 pp.

Paulson, D. 2009. Dragonflies and damselflies of the west. Princeton University Press. 535 pp.

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