Damselfly Dimorphism

Midsummer is a good time to photograph insects in Pennypack Preserve.  I have photographed a lot of butterflies in the past, so I went out the last week of July to look for something different.  I immediately noticed some damselflies which I didn’t recognize.  In particular I saw a damselfly with black wings and a distinctive white patch on the wing tips which I didn’t remember seeing before.  However, on doing some research I realized that it was the female version of a common damselfly, the Ebony Jewelwing (Calopteryx maculata).  It turns out that many damselfly species, like many birds, are sexually dimorphic, i.e. the males and females do not look exactly alike.  Like birds, some male damselflies may be more colorful than the females.  Male damselflies stake out territories at the breeding grounds over ponds or streams and drive off rival males.  The color may be a signal in attracting a mate, as it is in birds.

This is a picture of the Ebony Jewelwing male.

I see these commonly in midsummer.  The male has jet black wings and an iridescent greenish thorax and abdomen.

The damselfly I was seeing now looks like this.

The body is less green and there is a distinctive white patch at the tip of each wing.  These are female Ebony Jewelwings.  For whatever reason I saw only females on this trip, while in the past I have only seen males.  They obviously have to get together to mate, but these damselflies were likely hunting, since I took the pictures in a meadow and not near water where they would typically mate and lay eggs.   I don’t know if males and females have separate hunting behavior, or if this was just a coincidence.

Another common damselfly in Pennypack Preserve is the Blue-Fronted Dancer (Argia apicalis).

This is a male (holding a captured Acorn Weevil).  It has blue eyes, a blue thorax, and blue tip on the abdomen.  I saw these yesterday, but also saw some drab brown damselflies.

These are female Blue-Fronted Dancers.  Like many birds, the female has drab, presumably more protective coloring, while the male is more colorful.  The color is a risk to the male to be noticed and eaten by birds, but presumably increases its chances of mating successfully.

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