Early fall in Cowee Meadows

burying beetles, sweetgale ecology, and dragonfly sex

A trip to Cowee Meadows usually provides a curious naturalist with something to contemplate. It’s also a good idea to keep an eye out for large, brown, sometimes temperamental, mammals with claws or hooves.

A stroll out there in mid-August discovered several things of interest.

A desiccated toad carcass lay in the trail, cause of death unknown. The body was attended by two big, orange and black, sexton beetles, maybe just looking for a meaty snack but possibly foraging for a carcass on which to rear a brood of larvae. Sexton beetles are also called burying beetles; they bury the bodies of small mammals and birds (or chunks of dead salmon), denuding them of fur and feathers, which are used to line a chamber housing the carcass. Eggs are laid near the buried carcass and the larvae crawl into the food-filled chamber. Unusual among insects, both parents feed the larvae on liquefied, partially digested meat, as the larvae also feed for themselves on the stored carcass. The number of larvae feeding on a carcass may be regulated by parental infanticide; if there are too many for the available food pile, the parents reportedly reduce the numbers. If for some reason, a female beetle does not have an active partner, she can raise a brood by herself, fertilizing her eggs with stored sperm. In this case, the question in my head was whether or not a desiccated toad would make good larval meals.

The low wetland before the beach berm is thronged with aromatic sweetgale shrubs. They harbor symbiotic bacteria in the root system; the bacteria take atmospheric nitrogen and ‘fix’ it into a form that plants can use. This species usually (but not always) has male and female flowers on different individuals. Male plants have already set their flower buds for next year, while female plants bear cone-like structures with small one-seeds fruits attached to the core. Some small critter had feasted on the seeds of a few plants, leaving the cone-core and fragments in a heap. A fat green caterpillar grazed steadily along the edge of one leaf, not deterred by the reported insect-repellent properties of this species. I was interested to find out that two field guides and two tomes on the flora of Alaska do not instruct a field naturalist how to tell male from female flowers—but the Trees and Shrubs of Alaska by Viereck and Little does!

Out on the beach, it was time for tea and snacks on a favorite log. The tide was low, and far out on a distant rock there was a black lump, which turned out to be an oystercatcher, able to loaf now that the chicks have been raised.

Instead of hobbling over the cobbles around the point, the return trip came back through the grassy/sedgey meadow, where the trails of trampled vegetation left by wandering horses made easy walking in most places. Sparrows popped up out of the tall grass and quickly dove back into the next dense cover. Closer to the river, the vegetation is shorter and marsh felwort flowers began to show up, not only on gravelly soils (as the books say) but also in deep black muck.

The old trail next to the beaver pond has been abandoned, but the water level was very low; there was not even any water in the stream below the dam that makes the pond. That encouraged a little exploration at the edge of the wet meadow along the old trail, which was apparently built (or rebuilt?) without consideration of beaver activity. In recent years, beavers had raised the pond level so the trail was often flooded well over ankle-deep; water was often trapped between the log rails on the trail margins. Rows of young alders have now sprouted up along the edges of that trail, making most of it rather impassible. But the low water level made it quite easy to tromp through the sedges on a parallel route. The newer, improved trail along the hillside would still be the trail of choice most of the time.

Near the beaver pond, dragonflies zipped to and fro, some of them in copula. Male dragons (and damselflies) chase whatever female flies by. If a female is not interested, she may evade the male by running away or hiding; in some species she just plays dead! A successful male grabs a female behind her head with claspers at the end of his abdomen, and they may fly in tandem for a while. The female, if willing, bends her body under his to bring her genitalia (near the end of her abdomen) next to where he has previously stored his sperm in the anterior part of his abdomen, so sperm can be transferred. Copulating dragons make a circle or ‘wheel’ of their bodies. If the female had mated previously, the present male may try to scrape out the sperm of the first male; the ‘opinion’ of the female with respect to this action apparently has not been recorded.

Northern-Bluets-mating-by-bob-armstrong
Photo by Bob Armstrong

Some days later, I watched a pair of bluet damselflies in tandem, perched on a sedge blade in a mid-elevation muskeg pond. The female bent her body up to touch his, in the copulatory position, several times, but they did not form the mating wheel. Three other bluet males patrolled this pond, sometimes zooming in closely on the pair, and even contacting them, as if to try to steal the female away. This is a behavior I’d not seen before. At the edge of the pond lay a dead female, possibly drowned in the act of laying her eggs in underwater vegetation. Some bluets lay eggs in vegetation near or on the surface, but some species of bluet actually submerge the whole body while egg-laying, and upon occasion need to be pulled out by their partner or perhaps by a nearby unmated male.

Dragons and Damsels

extraordinary lives of odonates

A few days ago, I stood beside a small pond, watching showy insects zoom around. There was a small blue damselfly, checking out the weeds in the shallows. And there were two of its larger dragonfly cousins: a couple of big darners and several smaller emeralds, so-named for the intensely green eyes and greenish body of mature adults.

There are over 30 species of dragonflies and damselflies in Alaska, and in Southeast we have around 19 species (3 damsels and 16 dragons). As they become better studied, more species will probably be added to the lists. The state dragonfly is the four-spotted skimmer.

Dragon- and damsel-watching is an increasingly popular recreation. Even without bothering about taxonomic details and the minutiae of species identification (which commonly requires having the creature in hand), the behavior of these conspicuous insects can be fun to observe.

My own introduction to this group, collectively called odonates (”toothy”), came several short eons ago, when I was a graduate student. I was studying yellow-headed blackbirds in the marshy potholes of eastern Washington, where these birds, along with red-winged blackbirds, were abundant. Perhaps the most important prey the blackbird parents fed to their chicks were recently emerged odonates.

Odonate larvae are aquatic predators, capturing prey with a huge, extensible, hooked lip. They may spend a year or two, or sometimes more, in the water, feeding and growing.

Damselfly larvae breathe by means of three external gills at the back end of the slender body; the gills also help in swimming. Dragonfly larvae have internal gills, and they breathe through the back end of the digestive tract.

When they are ready to become adults, the larvae crawl up on a plant stem or rock, the larval ‘skin’ or exoskeleton splits open, and the new adult pulls itself out. Blood is pumped into the long abdomen and into the wings, which gradually expand and slowly harden. These newly emerged adults are called tenerals. They fly very weakly until their body and wings harden. So this is the stage of their life when they are extremely vulnerable to predators, such as the blackbirds. The blackbirds I was observing stuffed their chicks with tenerals all day long.

As fully mature adults, odonates are much harder for birds to catch. Odonates have four wings, which can be moved independently of each other, giving them great maneuverability in the air. Adult odonates are terrific predators of other insects, catching the prey in a basket formed by their spiny legs, and munching them up in strong jaws. They have huge eyes of multiple facets, which are fine motion-detectors. Some odonates hunt by almost constant flying and searching, and others are sit-and-wait predators, perching on a lookout spot and darting out after a passing bug.

Each adult flies for only a few weeks. During that time it forages and plays the mating game. Males of some species are territorial, defending part of a pond from other males, and waiting for females to visit. Others cruise around, looking for potential mates.

The mating process in odonates is unique among insects. The male produces sperm, which he transfers to a special chamber at the front part of the abdomen. He does this by bending forward and placing the tip of his abdomen at the entrance of the storage chamber. When he finds a female, he grabs her with special appendages on his ‘tail’, holding her by the top or back of the head. The pair may fly around in tandem for a while.

damselflies-mating-by-bob-armstrong
Bluets mating. Photo by Bob Armstrong

The female then loops her abdomen forward to connect with the special sperm storage chamber. In this circular or ‘wheel’ position, a pair may fly around some more. The sperm are transferred to the female, where they fertilize her eggs.

But that’s not all: females can mate with more than one male. Competition for females is intense, and males have a nifty way of beating out competitors. Their penis does more than transfer sperm. It also can remove or push aside the sperm of males that mated with this female previously. So, if this male is the last one to mate with her, he ensures that he is the father of her eggs.

In some species, the male stays with the female, either in tandem or nearby, keeping guard on his paternity while she lays the eggs. In other species, females just sneak off on their own and try to avoid getting grabbed by other males. Given what goes on in many birds and mammals, I have to wonder if some females might not let themselves get caught by a new male, if he looks like a better specimen and potential father.

Females lay their eggs in several ways. Some typically insert their eggs into plant tissue, using a sharp structure called an ovipositor (egg-placer). Other species just drop their eggs into water or dap them onto mud or moss.

It is easy to observe territorial aggression, tandem and wheel flights, and sometimes oviposition in these insects. Such behaviors are often easier to watch in odonates than in many birds.

Here are three nice introductory guides to odonate watching:

Dragonflies of Alaska (second edition), Hudson and Armstrong;

Introducing the Dragonflies of British Columbia and the Yukon, Cannings;

Dragons in the Ponds, Armstrong, Hudson, and Hermans (for children).