Saturday, June 13, 2015

Odonates in The Pearl: Tanner Springs Park

Over the years I have occasionally driven by Portland’s Tanner Springs Park and its enticing urban wetland, but I never made the effort to stop and spend some time during the odonate season—until recently. The park occupies a single city block in the heart of the Pearl District. If you’re not from around here, the Pearl District was once an area of warehouses, light industry, and rail yards known as the “Northwest Industrial Triangle”. This section of the city has experienced significant urban renewal since the mid-1980s and is now a vibrant area of commerce and urban residences.

Tanner Springs Park is not your textbook city park. It’s a great example of melding “wild” natural, “tamed” natural, and unnatural elements in complementary ways. About two-thirds of the park are what I would describe as unkempt—which is a good thing. It isn’t all manicured lawns, ornamental vegetation, and fountains. Check out the view at Google Maps.

Tuesday, June 9, 2015

The Rewards of Looking for Exuviae

Recently I was looking for odonates at a place called Grand Island on the Willamette River in Oregon. This is in Yamhill County which is one of the more under-surveyed counties in the state (only 24 species recorded at the time). I found a couple of new species for the county with little effort—Tule Bluet (Enallagma carunculatum) and Western Pondhawk (Erythemis collocata), both very common and widespread species in the region.

Male Tule Bluet (Enallagma carunculatum) on left, and immature male Western Pondhawk (Erythemis collocata) at Grand Island, Oregon.

Tuesday, September 3, 2013

ID Challenge #5 Answer

I didn’t give you much to go on in this challenge, but this odonate is identifiable based on what you see. Not only that, but the sex can be determined and, as I alluded to, a little more can be deduced—something that has happened to this individual, if you’re observant.

The first step is to identify which part of the bug we’re looking at, and I think it should be recognizable as portions of the compound eyes with thousands of tiny lenses, or ommatidia, producing that geometrically speckled look. The fact that these compound eyes meet at a long seam (the almost vertical black line) narrows down the possibilities to just one family out of all dragonflies and damselflies in North America: the darners, Aeshnidae. The eyes of all damselflies are separated by a gap; at most, the eyes of the other dragonflies meet at a very short seam, but some are separated by a gap or just meet at a point.

Wednesday, August 28, 2013

ID Challenge #5

At right is an extreme crop of an odonate photographed somewhere in North America—north of Mexico, to be quite ambiguous. I don’t think this one is too difficult to figure out, however what is visible in the image is one of those things which is easily unnoticed if you don’t look for it. Not only can this individual be identified to species, but also its sex and even a little more can be gleaned with some sleuthing.

Leave a comment to let me know what you think it is—the species and sex. If you can tell me anything more based on what you see in the image, include that as well. Comment moderation will be turned on until I post the answer, so they will not be visible in the meantime.

Have fun!

Postscript, 3 September 2013

This challenge is now closed. The answer with a complete discussion is here.

Friday, August 23, 2013

What's that little blue thing? (The Northwest Bluets)

Oh, the little damselfly that has a blue thorax with black stripes and an alternating blue-and-black pattern on the abdomen? That’s a bluet. Which one? Umm...

A generic Pacific Northwest bluet (Enallagma). Note the abdomen
with an alternating blue-and-black pattern, the thorax with blue
and black stripes, and blue postocular spots on top of the head.
Eight species of bluets (Enallagma) are recorded in the region composed of Oregon, Washington, Idaho, and British Columbia and, superficially anyway, they all look alike with their alternating blue and black abdominal pattern and blue and black striped thorax. They really all look alike if you don’t know what to look for, but I’m here to help. I’m not going to explain how to identify each of those eight species in this post—there are field guides and manuals for that, but I’ll give you a few tips to help you narrow down the choices.

Thursday, December 6, 2012

ID Challenge #4 Answer

Click image for a larger version.
Ready for the solution to ID Challenge #4? Let’s start at the top as we consider this mystery Pacific Northwest odonate: Is it a dragonfly (Anisoptera) or a damselfly (Zygoptera)? Probably most people can take a glance and immediately recognize it as a dragonfly, but how do we know for sure?

It looks pretty bulky, the “face” looks relatively flat rather than “snouted”, and the head does not seem very elongated from side-to-side (hammer-headed or dumbbell-shaped with the eyes capping each end). These are all indicators of dragonflies, but another more concrete character is the width of the gap between the eyes at the top of the head. On damselflies that gap is greater than the diameter of either eye; on dragonflies, if a gap is present, it is less than the diameter of either eye. Even at this angle we can see that the gap is smaller. Definitely a dragonfly. You can also just make out that the margin of each eye is angular at the narrow point of the gap—something else you won’t see on a damselfly. Here’s a post I did a while back on differentiating dragonflies and damselflies which illustrates the head/eye shape.

Saturday, December 1, 2012

ID Challenge #4

Wow, it’s been a long time since we’ve had an ID Challenge! Here’s a close-up of some mystery odonate which is found in the Pacific Northwest (or parts there of). Where else does it occur? I’m not saying. If you’re familiar with the species, it ought to be pretty easy. If you’re not familiar with it, it’ll take a bit of research.

Leave a comment to let me know what you think it is. Comment moderation will be turned on until I post the answer, so they will not be visible in the mean time.

Have fun!

Postscript, 6 December 2012

This challenge is now closed. The answer with a complete discussion is here.