The BugLady likes to “bug” (if birders “bird,” can “bug” be a verb for folks who are looking for insects?) along the Milwaukee River at Waubedonia Park because (surprise) it’s great for dragonflies and damselflies – she’s photographed 25 species there. Most productive are the small bays along the shoreline where water lilies and arrowhead grow and the current is negligible, but she’s also written about the crowds of ovipositing Powdered Dancers that favor submerged aquatic vegetation in the currents near shore.  

About the time that the Powdered Dancers are peaking, the beautiful Stream Bluets are, too, and the vegetation along the riverbank flickers with tandem pairs. Males are “black-type” bluets – of the 35 similarly-marked and frequently-confusing species of bluet damselflies (17 species in Wisconsin), most are, as their name suggests, blue on some portion of their bodies. For “ease of identification,” they’re sorted into black-type, mid-type, and blue-type bluets based on the amount of blue in the male’s abdomen. However much blue is or isn’t there, the abdomens of most male bluets (except for the few that are red or orange) are tipped with blue, and the Stream Bluet has a deep “V” cut in the top side of that blue. 

Female Stream Bluets, sometimes described as drab, have lovely lime-green bodies (unless they are blue-morph females) and a line along the thorax that the books call brown but that always looks gold to the BugLady. Unlike most species of bluets, female Stream Bluets also have some blue at the end of the abdomen. 

Stream Bluets (Enallagma exsulans) are in the family Coenagrionidae (the Narrow-winged damselflies) and in the genus Enallagma, the American bluets. With a few exceptions, family members tend to prefer the edges of lakes or ponds ringed with vegetation, and except for picking moving water over still, Stream Bluets lead a fairly typical bluet lifestyle. Stream Bluets chase their prey – tiny insects – through the vegetation, making short forays in sheltered areas, but some fly out and hover over water.  

Females may oviposit alone or with the male still clasping the back of her head (contact-guarding – to keep her from being swiped by a rambunctious rival male). She extends her abdomen to , but if she goes under completely (she may stay down for a half-hour), the male will let go. The eggs hatch soon after, the naiads feed, and the almost-mature naiads overwinter. 

And Rivers ……. a rumination

If you could cut a cross section of a river, you’d find a seemingly infinite number of habitats and microhabitats in it, each formed by a specific combination of factors: water depth, the topography of the river (there’s a difference between the current in the “inside curve,” the “outside curve,” and middle of a river), erosion, the makeup of the bottom/substrate (smooth, rocky, pebbly, leafy, littered with tree trunks, etc.), types and locations of aquatic vegetation, the strength of its current, water quality (amount of dissolved oxygen and other gasses, sediment, pH (acidity), chemicals, and pollutants), light, temperature, available nutrients, and influences of the land at its edges and upstream. None of these factors is static – most can change quickly and drastically, and sometimes permanently. And, because of the dynamics of water, if you cut another cross section 100 feet up or downstream, it would probably look different. Each of those habitats and microhabitats is attractive (or unattractive) to a particular set of organisms. 

The same is true of a prairie or woodland.

Insects that live in rivers, either as immatures or as “lifers,” have the same needs as those that live in quiet waters – oxygen, food, some elbow room, the ability to get around, the need to hide from predators, a way to keep excess water out. A wide array of adaptations – of different ways to accomplish the same goal – allows a wide array of invertebrates to live successfully in the same habitat without using each other’s resources. River dwellers have an additional requirement – in water that is always moving, they need a way to stay put. 

Waubedonia dragons and damsels oviposit in their favorite slice of habitat and their naiads spend about a year ambushing their prey as they sprawl on underwater rocks, plant leaves, and stems or while they hide in muck and debris on the river bottom. 

“If the creek don’t rise,” they will complete their life cycle in the same area, but the creek does rise, sometimes dramatically.

How do you even study something like this? It’s hard to investigate the effects of flooding when floods are, often, sporadic and unpredictable. When the BugLady started researching this, she expected that she might find a few notes from disgruntled grad students saying “I was studying the macroinvertebrates of X River and we had a big flood and my plots were swept away and the bugs are all gone.” But there wasn’t much out there (thanks, BugFan Bill, for helping to find and access some research). There were a few studies/observations of flooding with respect to mosquito populations, and to Odonates as potential biocontrols of mosquitoes and as indicators of aquatic ecosystem health.

Whether from a summer storm or spring ice melt, floods mix things up. After the initial blast of a flood, there can be long-term fallout. Among many other effects, floods revise/scour the contours and textures of the river bottom, carrying away nutrients and shelters (but then delivering more), reshaping channels and changing currents, removing  predators (and delivering more), and putting a load of silt into the water that cuts down light for photosynthesizing plants, and settles on underwater surfaces – including invertebrates. 

The BugLady is stunned by the enormity of the changes that a flooding event may trigger for critters that are a half-inch long and less. Their ability to stay in place depends on whether they can get out of the current fast enough, so species that lead a sheltered life on the downstream side of a rock or tree trunk are at an advantage, but more mobile individuals must literally swim for their lives, and those that are weak swimmers don’t stand a chance of staying put. 

One study showed that in a single spring thaw event in New Zealand, 50% of the macroinvertebrates were washed away! Another postulated that populations bounce back pretty fast after flooding as larvae that took shelter move back to their micro-habitats, and that the ability to take steps to avoid being washed away may impact a species’ fitness and persistence.

When the Urban Ecology Center in Milwaukee County records a new dragonfly species along the river, is it a gift from upstream?

The BugLady is still wrapping her head around this.  So many moving parts.

The BugLady

The post Stream Bluets and Rivers appeared first on Field Station.

Howdy, BugFans,

Back in the summer of 2019, in an episode about Lilypad Forktail damselflies entitled “A Species on the March,” the BugLady wrote, “Lake Twelve is famous because of the presence there of not one, but two rare (in Wisconsin) damselflies – the Slender Bluet and the Lilypad Forktail. The bluet has been on and off of our state radar since 2007; the forktail was first recorded at Lake Twelve in 2017 but has been seen intermittently in Wisconsin since 2010.”

The property on the west end of Lake Twelve is part of the Biehl Nature Preserve, one of the Ozaukee Washington Land Trust preserves, and along with these two species, there are lots of other dragons and damsels around (the pier is often partly submerged, so dress accordingly).

This is the story of the Slender Bluet.

Bluets are members of the Pond or Narrow-winged damselfly family Coenagrionidae – with 105 species, it’s the most common damselfly family. In Wisconsin, the family includes the bluets, dancers, forktails, and sprites, and the (enigmatic) . The Pond Damsels are a colorful bunch, with males more vivid than females. Adults tend to perch near the ground (routinely below the BugLady’s knee level), and they fold their wings over their abdomen when they perch. Various species of Pond damsels are in the air from late spring to late summer – they (mostly) aren’t long-distance flyers, and males are not territorial. Some species overwinter as eggs and others as naiads, and they are tolerant of cold and freezing at the north end of their range.

A study of the naiads of a New Zealand Pond damsel revealed an array of body language used by the naiads to communicate predation threat, competition, and territorial behavior.

Canadian Naturalist John Acorn calls bluets “floating neon toothpicks.”  The American bluets are all in the genus Enallagma, but we also have a few species of Eurasian bluets in the cosmopolitan genus Coenagrion. Most male bluets have bodies that are blue and black in varying proportions – for “ease” in identification, they are artificially divided into the “black-type” bluets, the “intermediate-type” bluets, and the “blue-type” bluets. Females are a different ballgame – they are not brightly-colored, and while some species have identifying markings, others enjoy different color phases, and their ID is often up for grabs. Unless you have a hand lens.  And, alas, some of , too.

For their bluets choose unpolluted still or slowly moving water with plenty of submerged vegetation. Eggs are inserted into plant stems and the naiads (categorized as “engulfing predators”) climb around among the plants and ambush their prey, which includes any aquatic critter smaller than they are.

Slender Bluets (Enallagma traviatum) aren’t from around here, historically. The species is divided into two subspecies; one (Enallagma traviatum traviatum) occurs on the east side of the Alleghenies/Appalachians and the other, Westfall’s Slender Bluet (Enallagma traviatum westfalli) on the west. It is an Eastern, or maybe Southeastern, species that is moving west and north – an account from Vermont, where it was first seen in 2001, called it “another southern species that may be expanding into our region.” It was first recorded in Wisconsin in 2007, and since then there have been 70 reports from just a few locations in about 20 counties in Wisconsin, with sightings getting more numerous in the past three years (thank you, lovely, searchable database. Its status is listed by the Wisconsin Natural History Inventory as Critically imperiled/Vulnerable due to its restricted range and relatively few populations – understandable in an animal that’s in the early days of establishing itself here. Among dragonfly enthusiasts, it’s listed as a “Most Wanted” species.

This is a beautiful, “black-type” bluet whose blue is a striking sky-blue (except for the lilac-hued tenerals (juveniles). Males have a, and in females that stripe is interrupted by a slim, blue line down the middle.  They’re about 1 ¼” long, and they have very large, very blue eyespots/postocular spots – pigmented patches on the tops of their eyes. The male’s claspers are described as “” (along with a few other features, eyespots and claspers are used in identifying bluets). Here’s a .

Look for them from mid-June through July in Wisconsin.  Robert DuBois, in Damselflies of Minnesota, Wisconsin & Michigan (the successor to Damselflies of the North Woods) tells us that “males frequently hover over open water, sometimes while in tandem with the female” and that “oviposition usually occurs into vegetation at the water’s surface with male contact-guarding in sentinel position, but female sometimes descends alone to oviposit into plant stems.” Bugguide.net says that “Tandem pairs will gather by the dozens perched on stems above the water or staking claims out over floating vegetation,” and the BugLady found numerous pictures of , reminiscent of Powdered Dancers. Like the other bluets of our area, they overwinter as naiads.

When they pick a spot to oviposit, some Odonates (dragons and damsels) avoid bodies of water that contain fish, but Slender Bluet naiads can be found in fishy waters. The naiads have been subjects in a number of experiments designed to gauge the survival of naiads whose main predators are fish (bluegills) vs those that are preyed on by the hefty naiads of Common Green Darner dragonflies. Some experiments compared Slender Bluet naiads with those of Azure Bluets, and others compared Slender Bluets with forktail naiads.

Some outtakes:

• With some overlap, one set of bluet species lives in ponds with fish; and ponds without fish support a different set.
• The presence of fish inhibits feeding excursions by damselfly naiads.
• Naiads from fishless ponds move quickly and conspicuously; naiads from fishy lakes (like the Slender Bluet) and from fishless lakes with darner naiads move slowly and are more hidden.
• Bluet naiads from fishy lakes, including Slender Bluets, tend to ignore darner naiads – and often get eaten by them.
• When predaceous fish are around, the species composition of a pond community favors species that are harder to find.

The BugLady was curious about the species name traviatum, but her digging didn’t get her very far. She couldn’t find a meaning for “t�����������ٳܳ�,” so she looked up “traviata” and got lots of references to the opera, plus a few baby-naming sites that informed her that Traviata means “corrupted” or “led astray” (and so, is an unlikely candidate for inclusion on future “10 Most Popular Girls’ Names” list).

*BOTW will not appear on February 7 but will be back in action on February 14. *

The BugLady

The post A Species on the March – Part 2, the Slender Bluet Damselfly appeared first on Field Station.