green darner, Washington state insect

Most states don’t have state insects, and most people in Washington state don’t know about our very own state insect! Do you know what it is? You probably do by now, having seen all the photos, but you may not know its name. It’s the Common Green Darner, Anax junius. This species is a member of the family Aeshnidae, suborder Anisoptera, order Odonata. This insect order contains the dragonflies and damselflies.

In 1997, a group of students at Crestwood Elementary School in Kent brought the idea of a state insect to the legislature. About 25,000 students from over 100 school districts statewide were asked to pick a state insect from among several contenders, and the dragonfly won in a landslide.

Male Common Green Darners are easily recognized by their green thorax and mostly blue abdomen. Females are similar, but the abdomen is usually greenish (rarely blue). Common Green Darners are the only North American darner in which the pair stays connected after mating and flies around in tandem while looking for places to oviposit.

Common Green Darners are among the best-studied of North American dragonflies. They occur all across North America, breeding in ponds and lakes from southern Canada to southern Mexico, as well as in Hawaii. They are known to be highly migratory throughout their North American range. Mature adults arrive rather early in spring at the north end of their range, often the first dragonflies to be seen in flight each year. They breed and lay eggs as long as they live, then die after a few weeks. Their eggs hatch and their larvae develop in the water through the summer.

In Washington, as elsewhere in the North, the larvae have grown rapidly in the warm-water environment and are ready to emerge from the water in August. There is usually a hiatus in summer where not many are seen, but then immature individuals, colored like adults but with a reddish-violet abdomen, become common. After their emergence, you can see their exuviae (cast skins) along the edges of wetlands everywhere.

The immature Anax very soon begin to head south. Obvious migratory movements are rarely seen in Washington, but farther south in California, Common Green Darners can be everywhere in fall. They move through the landscape in numbers, steadily heading south.

If you wander through Florida or southern Texas in September and October, Common Green Darners are ubiquitous. These are end points in the long migration, and by the time the migrants reach these lower latitudes, they have attained sexual maturity and are ready to breed. They do so, and – to make a long story short – their larvae mature through the tropical winter and are ready to emerge in spring. These spring emergers then head north to repeat the annual cycle.

So in this dragonfly, there are two alternating generations, one that emerges in fall in the north and flies south, another that emerges in spring in the south and flies north. Thus this species shows an amazing and unique migration pattern, unlike that of any other animal. At first glance, it seems something like the migration of Monarch butterflies, but it is actually somewhat different.

In Monarchs, northern adults that emerge from their chrysalis in the fall head south and winter in southern Mexico. These same individuals begin a northward migration the next spring, so in that way their migration is more like those of birds. But they stop and breed somewhere in southern US, then their offspring continue northward and do it again. There may be three generations of northbound migrants, then, as they emerge from their pupae late in the summer, the offspring of the northernmost breeders head south instead. There are indeed similarities to the darners in that more than one generation is involved in the annual cycle, and the northernmost breeding populations have a northbound and a southbound generation.

But it turns out that the darners have been varied in the evolution of their annual cycles. Larvae growing rapidly through the summer in Washington emerge in fall to fly south, seemingly the most common mode, while those growing more slowly are forced to overwinter as large larvae and emerge the next spring. Thus there is also a “resident” population of individuals with a life cycle more like other dragonflies, that is they fly during the summer and their larvae develop during the winter. It was hypothesized that these two populations might even show genetic differences because they didn't interbreed. However, recent studies have shown that the migratory and resident populations are genetically identical.

With global warming, the summer growing season should lengthen, possibly causing further variation in the life cycle of this interesting species.

Dennis Paulson

Dragonflies in autumn

Dragonflies are insects that love warmth, so the adults fly through the spring, summer, and fall and disappear in winter, overwintering in the larval stage in the water or as eggs in the case of a few species. The best month in which to see dragonflies in the Pacific Northwest is July, when the spring species are still around, summer species are in full swing, and the first of the fall species are appearing. By the end of August, when these photos were taken, the spring species are gone, the summer species are waning, and fall species dominate.

Certain groups are especially common in fall. The big blue darners (Aeshna) peak in August and September, when we see them in numbers at just about any wetland. The males are looking for females, and they alternate flying along the shore and hovering in one spot, occasionally dipping down into the aquatic vegetation to see if they can spot an ovipositing (egg-laying) female. When two males intersect, there may be a fierce chase. When a female is spotted, the male grabs her and mating takes place, usually up in the trees and often lasting an hour or more. The female will soon make her way back to the water and lay her eggs in plant stems or rotten wood.

Another common group in the fall are the meadowhawks (Sympetrum), members of the skimmer family (Libellulidae). These little dragonflies, most of them red, fly in numbers around just about all lentic wetlands. (Lentic = still, such as ponds and lakes; lotic = flowing, such as streams and rivers.) One species, the Cardinal Meadowhawk (Sympetrum illotum), flies throughout the summer and can be recognized by its very bright red color and orange-suffused wings with a dark streak at the base. This species breeds in permanent ponds and lakes, and a larva, after hatching from the egg, develops over the summer, goes into dormancy in the winter, then emerges as an adult the following spring. If it develops especially rapidly, it will emerge in the fall, and it thus has a bimodal flight season, common in spring and fall and less common in midsummer.

But most meadowhawks don't emerge as adults from the water until July or August, then fly well into October. Another very common species is the Striped Meadowhawk (Sympetrum pallipes), recognizable by its striped thorax. The individual shown here is a bright red female, colored just like a male, but other females are brown. This is another example of polymorphism, with red and brown morphs, and we can only speculate on the factors that cause the evolution of such color variation. This species breeds in temporary wetlands that often dry up during our relatively dry summers. The females drop their eggs while in flight around the edge of these wetlands, usually on dry ground. Then the wetlands flood over the next winter, inundating the eggs, and they hatch in early summer when temperatures are high enough. They develop quickly and emerge in midsummer, and the adults fly during the fall, repeating the cycle. Two related species can have quite different life histories.

Dennis Paulson

a day at the coast

Hello, all.

This is the first post from the Slater Museum of Natural History at the University of Puget Sound in Tacoma, Washington, USA.

These posts will be varied, but the theme is Northwest nature, information about natural ecosystems of the Pacific Northwest and their plants and animals. We encourage anyone with interest in this subject to join the blog and contribute to it. We also encourage civility and respect for the opinion of others. As most of our material will consist of facts rather than opinions, that should be easy!

I'm writing about a trip to the outer coast of Washington on 30 August 2009. Netta Smith and I wanted to get out of the house and see how the coastal bird migration was faring. It turned out there wasn't much migration going on, at least at most of the places we visited. We drove to Westport first, all the way at the end of the road around the marina to check out the breadth of Grays Harbor with our spotting scope. Out in the middle there were vast flocks of birds, underscoring the value of coastal estuaries for marine life. There must be a lot of prey out there to support hundreds, maybe thousands, of Brown Pelicans, Double-crested Cormorants, California and Heermann's Gulls, and Common Murres, all fish-eaters. There were also smaller numbers of Western Gulls, Pigeon Guillemots, and Rhinoceros Auklets on the relatively calm waters of the harbor. Heavy cloud cover made for gray sky and water, but visibility was good.

Small numbers of Brandt's and Pelagic Cormorants were roosting on channel markers and rock jetties, perhaps the beginning of the large numbers that arrive from the south each fall. No ducks, loons, or grebes were seen; they are yet to come. The only shorebird present was a welcome one, a juvenile Wandering Tattler (PHOTO) that probed among the rockweed. This bird is a far-journeying species that breeds in the Alaska mountains and winters on islands of the South Pacific, north to Hawaii and California. They pass along the Washington coast in small numbers every spring and fall, enhancing the sound of the ocean breaking on rocky shores with their loud, ringing calls.

Below us on the same rocks were scattered ochre seastars (Pisaster ochraceus), one of the dominant intertidal invertebrates in Pacific Northwest coastal waters. This is a polymorphic species, occurring in orange and purple morphs. We noted that the orange ones were very conspicuous, even below the water, but we didn't see the purple ones until the waves receded, exposing them, and even then we had to look quickly, as they blended with the rocks and algae. Why is the species polymorphic? Why are the purple ones more common here, when the orange ones are more common in Puget Sound? Does it have anything to do with their conspicuous to potential predators? One thing that Mother Nature bestows on us is a never-ending series of master's and doctor's research topics!

We headed for the ocean beach south of Westport. In some areas, driving on the beach is permitted, and that's a great way to see birds. Unfortunately, as our population has increased, too many of us are doing this now. We were shocked to see how many people were scattered along the beach. There were no shorebirds (sandpipers and plovers) at all, but there were roosts of hundreds of gulls of three species (Western [PHOTO], California, Heermann's) all along. As we would approach one of these roosts to try to get some photos and check for rare species, more times than not one or more people would walk right up to the birds, scaring them away. More often, a frolicking dog or two would do the same, and it was obvious that the resting gulls were irresistible to people and dogs alike. "Oh boy, let's go scare up those birds." If this was an opinion blog, I would relate in no uncertain terms what I thought of those people! Sharing the beach is great, but this wasn't sharing. Imagine just sitting down on your favorite couch to relax and digest your dinner, and someone comes running through the living room and says "up, up, up," so you walk around the house three times and then sit down again. Within a minute or two the pest comes again, and the scene is repeated. Some of the flocks were disturbed so often that I wondered, not for the first time, how birds and other wildlife will manage in the long run to coexist with our own species.

After this frustrating experience at several beach-access points, we motored down to Tokeland to look for the large roosting flock of Marbled Godwits and other shorebirds that are often present at the marina. Perhaps for the first time ever, there was not a single bird present. Other birders who we encountered had seen none of them earlier in the morning, and we arrived right around high tide, when the birds should have been roosting. But it was a low high tide, with plenty of mud flats in Willapa Bay still exposed, and why roost when you can feed? Shorebirds in migration feed until they are stuffed, laying down fat deposits all over their bodies, and after a few days of this, taking off on the next stage of their flight, often hundreds or even thousands of miles. They can burn their fat for "food" as they fly, and the longer they fly, the lighter they get!

Shorebirds are the world's best optimizers when it comes to feeding. A sandpiper's bill may actually be probing the substrate as it is coming to a landing, and they never stop probing, as long as there is a bit of room in their stomach. Many species have sensitive nerve bundles called Herbst corpuscles in little pits on their bill tip, and they can feel the wiggle of a worm or the curve of a snail as they probe the sand or mud.

Our final stop of the day was at Bottle Beach State Park on the south side of Grays Harbor, and that's where the migrants were. Flocks of hundreds of Western Sandpipers flew to newly exposed mud flats as the tide receded, and scattered among them were Semipalmated and Black-bellied Plovers, Whimbrels, Greater Yellowlegs, and other species. The sun never came out this day, but there were just enough birds that we headed home with a sense of accomplishment. Of course the birds were the ones accomplishing.

Dennis Paulson