Cordulegaster diastatops, Delta-Spotted Spiketail

& Cordulegaster bilineata, Brown Spiketail
Cordulegaster diastatops and Cordulegaster bilineata

 

 

Family: Cordulegastridae

Length: both species typically 60-65 mm

 

A Note About These Two Species

The Delta-Spotted Spiketail and Brown Spiketail are closely related and very similar in appearance. Some Odonatists believe that the Brown is not a legitimate species, but only a sub-species of the Delta Spotted. Others disagree.

Some writers state that the two species can be determined by certain traits seen in the field or in photographs. Others are emphatic that only microscopic examination of a specimen can accurately determine which of the two species is in hand.

To make matters worse in some areas (West Virginia, for example), many experts say that individuals display traits that are intermediate between Delta-Spotted and Brown Spiketails.

Our recommendation to dragonfly watchers and photographers is to refer informally to the individuals you see as Delta-Spotted Spiketails. In more careful record-keeping, record them as Cordulegaster diastatops/bilineata.

In the description on this page, we will refer to Delta-Spotted Spiketails. At the bottom of the page we will discuss certain traits, visible in the field, which may (or may not) allow Ode enthusiasts to separate Delta-Spotted from Brown Spiketails.

The Delta-Spotted Spiketail has a black abdomen with yellow triangular spots on the dorsal surface. The eyes are green and nearly touch each other. The sides of the thorax are black with straight, broad, yellow stripes.

Females and males are colored and marked similarly, but the female has an ovipositor that extends beyond the end of the abdomen.

While not rare, the Delta-Spotted Spiketail is, as Sidney Dunkle has observed, "not commonly seen except at just the right time and place."

Look for Delta-Spotted Spiketails at bogs and seeps and along streams.

Delta-Spotted Spiketail, Cordulegaster diastatops
Look for green eyes that almost touch, straight and broad yellow stripes on the sides of the thorax, and triangular spots down the abdomen.  

 

Delta-Spotted Spiketail, Cordulegaster diastatops

 The eyes nearly meet. The face is greenish to white, with a black line across it.

Delta-Spotted Spiketail, Cordulegaster diastatops

Above: The spots that give the Delta-Spotted Spiketail its name.


Can You Tell the Difference in the Field

Between Delta-Spotted and Brown Spiketails?

 

In his book Dragonflies Through Binoculars, Sidney Dunkle describes the following differences between Delta-Spotted and Brown Spiketails. Note that some other experts insist that only microscopic examination can really separate the two species. Also note that in some areas many individual dragonflies seem intermediate between Delta-Spotted and Brown.

Delta-Spotted

Brown

Body color black Body color brown
Triangular spots are pointed Triangular spots are blunt
Usually has three lateral thoracic stripes Has two lateral thoracic stripes
Of the lateral thoracic stripes, the posterior one is widest The lateral thoracic stripes are equally wide

These can prove challenging to apply in the field. When I find an individual, it is typically brownish black, with two thoractic stripes but an added spot or dash, triangles that are bluntly pointy, and so on.

Unless the individual you are watching fits very clearly into the left column above, or the right, on all four points, it is probably best to record your find as "Cordulegaster diastatops/bilineata." The more careful record-keepers will use that designation for any of these Spiketails that was not examined microscopically.


Note: This is both the species page for Cordulegaster diastatops and C. bilineata, and the family page for Cordulegastridae

American Insects site