Wednesday, April 29, 2015

Rambur's Forktail

One of the first odonates we see each year is the Rambur's Forktail.  In terms of coloration, it is similar to the Western Forktail that is common in Washington – green thorax with a blue tip to the abdomen – but the ranges are quite different.  Notice that the abdomen is black above and yellow below, with a nice straight line demarcating the two colors.  Here's a look at a male Rambur's Forktail:

A male Rambur's Forktail at the Gilbert Water Ranch.  Notice the hamules under segment 2 of the abdomen.

The eyes are similar to those of the Pacific Forktail – black above and greenish-blue below.

Female Rambur's Forktail can look a lot like a male, in which case they are said to be andromorphic (male form).  An example is shown below:

An andromorphic female Rambur's Forktail at the Gilbert Water Ranch.

Notice the flat bottom to segment 2 (S2) of the abdomen.  Thus, this individual lacks hamules, which indicates clearly that it is a female.  In the photo of the male above, the hamules are seen prominently on the bottom of S2.

Females can also look different from the males, and in this case are referred to as heteromorphic (different form).  Here's an example:

Heteromorphic female Rambur's Forktail.

Notice the orange thorax with the black front stripe, and the lack of hamules under S2.  As this individual matures it will become more greenish-brown.

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