Tuesday, September 3, 2013

A Few Notes on Water Nymphs

It's inevitable that the "bugs" which generally pique the interest of most people are the adult form of the insect. The colorfully patterned wings of a butterfly or the iridescent elytra of a beetle that catch our eyes do so because in many cases insects are flying around trying to attract attention – that of a potential mate. The colors might be aposematic, bright, bold and arranged in striking patterns, a warning saying "don't mess with me". Or as often as not, an insect gets noticed because it's just plain weird and bizarre, it's so different that it almost qualifies as an alien form of life.

Ditto for dragonflies and damselflies – they're generally large or colorful, and pretty hard to miss on a visit to a river, lake or wetland. But the reality is that the odonates we see flying around are actually near the ends of their lives, on average lasting for only a couple of weeks before succumbing to predation or bad weather. Larger dragonflies such as darners can spend two or three years in their larval state, and by focusing only on the adult insects one is missing out on understanding most of their life cycles and roles in nature.

The following notes and photographs, not to mention the rest of this blog, are the work of a beginner who has taken only the first few steps down the long and never-ending road of learning. If you've had a close encounter with a cool naiad that's new to you and you're looking for a definitive answer as to species you've come to the wrong place, instead, try one of the links to the keys for identifying odonate larva further down this page.

Damselfly naiads are generally smaller than dragonfly larvae and have three external gills at the tips of their longer, slimmer abdomens. This is the larva of a Pond Damselfly, family Coenagrionidae.

The naiads of family Lestidae tend to be larger. Based on the habitat where it was found – a vegetated marsh – this could be a Northern Spreadwing (Lestes disjunctus), Sweetflag Spreadwing (Lestes forcipatus), Slender Spreadwing (Lestes rectangularis) or Amber-winged Spreadwing (Lestes eurinus).

The riparian habitat and very long basal segments of this naiad's antennae indicate family Calopterygidae. There are two possibilities locally – the Ebony Jewelwing (Calopteryx maculata) and the less commonly encountered River Jewelwing (Calopteryx aequabilis). According to Odonata Larvae of Michigan – Key to the Calopteryx Larvae of Michigan ~ "... tubercles behind eyes prominent and acute ..." ~ looking at the oblique views the spine behind the eye is clearly prominent and acute. This is the aquatic avatar of Calopteryx maculata.

Dragonfly naiads are stouter and more robust than their damselfly cousins, and their gills are internal (in other words, they breathe through their asses). This is a typical dragonfly larva, and based the adults of the species observed at the heavily vegetated lakeshore habitat and the naiad's profile it's a Skimmer, family Libellulidae.

Dozens of exuviae can be found during the summer months at the same lakeshore habitat. It's often advantageous to study exuviae as opposed to larvae since they can be examined and photographed without fear of hurting or killing the insect. Based on their general outlines these are Libellulidae exuviae, probably one of the common larger species such as the Widow Skimmer (Libellula luctuosa), Halloween Pennant (Celithemis eponina), Eastern Pondhawk (Erythemis simplicicollis) or Blue Dasher (Pachydiplax longipennis).

Celithemis eponina ~ can be ruled out, its eyes taper to conical points.
Pachydiplax longipennis ~ lacks the prominent dorsal spines.
Erythemis simplicicollis ~ "... lateral spines absent ..."
Libellula luctuosa ~ best guess, but most of the information needed for an exact ID is not in the photo. Next year I'll try to keep an eye out for emerging adult dragonflies, and it shouldn't be too difficult to capture the exuviae.

Identification to the species level might be difficult, but dragonfly naiads and exuviae can be narrowed down to as to family based on their general shape. This relatively stout exuviae is another example of family Libellulidae, and according to the Odonata Larvae of Michigan – Meadowhawks it keys out as a Ruby Meadowhawk (Sympetrum rubicundulum).

The best means of being certain as to the identity of an exuviae is to observe the eclosion or emergence of the adult dragonfly. This exuviae was left ehind by a Whitface – Leucorrhinia spp. – probably a Frosted Whiteface (L. frigida) as it's by far the most common of the Leucorrhinia species observed at the marsh where the exuviae was collected.

And about an hour and twenty minutes before it was photographed, this cast-off exoskeleton was worn by a female Four-spotted Skimmer (Libellula quadrimaculata).

Early last month I posted images of some family Cordulegastridae naiads. The shape of the naiads is distinctive and unmistakeable, but I have yet to encounter adults of this species (whichever one it may be!) and without having discovered the naiads would have no idea they were in the area – a great example of why the study of the naiads and exuviae is worthwhile.

And three years ago I uploaded a sequence of photos (taken by Pauline Campbell) of a Dragonhunter making its final molt to adulthood. In this case the profile of the exuviae is not typical of most Gomphidae, the burrowing larvae of Clubtails tend to be somewhat slender rather than broad and leaf-like.

Cruiser naiads are long-legged and spidery in appearance. There are two possibilities in this area – the Swift River Cruiser (Macromia illinoiensis), and the more commonly encountered Stream Cruiser (Didymops transversa). Due to the limits of the camera's macro (Canon PowerShot A530) and lack of experience in knowing what characteristics to photograph and/or observe when in the field I was unable to resolve the identity of the naiad to the species level ~ Aquatic Insects of Michigan – Macromiidae - Cruisers.

However, the experts at BugGuide.Net identified this Cruiser naiad right down to the sub-species level (perhaps based on the length of the lateral spines on S9?). Depending on which book or authority you want to follow, it's a Swift River Cruiser a.k.a. Illinois River Cruiser.

You've got to love that cute little frog-like face ...

After the photo session the naiad was released. The insect's colors are much more vibrant in its natural setting, however, underwater photography introduces greens and blues reflected from the sky and water.

Darner naiads and exuviae have relatively large eyes, and long but robust abdomens. By studying the images of the prementum, labial palps and blades posted at BugGuide.Net, I was able to ID this exuviae as belonging to a Canada Darner (Aeshna canadensis).

There were about a dozen of these dark exuviae clinging to a bridge over the fast moving water of the Moira River. Three of the images below are of an exuviae that belonged to a female – note the ovipositor.

BugGuide.Net to the rescue again ... the cast-off exoskeletons were left behind by Fawn Darners (Boyeria vinosa). I should have figured, both by the general aspect of the exuviae and because I was starting to see adults flying.

Thus endeth this lesson in how little I know ... and there's still a long way to go ...