Face-off

You rarely see two male dragonflies get this close without doing battle.

The male 12-spotted skimmer on the right attempted to usurp this perch from the male on the left, but was chased away.

The male 12-spotted Skimmer on the right attempted to usurp this perch from the male on the left, but was chased away.

There is a reason the male on the left wants that particular position — it’s somewhat shaded, and it’s a hot day with the sun directly overhead and high humidity.

Notice how the dragonfly has flexed his abdomen downward and perches behind the stake to shade himself somewhat.

Notice how the dragonfly has flexed his abdomen downward and is perched behind the stake to shade himself somewhat.

When he is perched this way, it gives me a much better look at his whole face. Now all we need is some names for those parts.

12-spotted skimmer face

Here’s a diagram I made in Photoshop that I hope accurately labels the parts.

12-spotted skimmer head-labeled

Starting at the top, you can see the short antennae emerging just above the darkened area of the vertex (triangle between the eyes), in which the primary light sensing ocelli are placed. Ocelli (there are three of them) are simple eyes (i.e., not compound) are used to detect changes in light intensity and duration, not for visual acuity.

The front of the dragonfly’s “face” is composed of the dark, bumpy frons and the much paler, two-segmented clypeus, which lie above the upper lip or labrum (looks like a mustache on this dragonfly).  This part of the face is the only part we usually see in horizontally perching dragonflies.

The real chewing apparatus of a dragonfly is composed of the mandibles and the maxillae (probably named for their similar roles in mammals) which lie directly below the labrum.  They are attached at the side of the head, coming together in the middle for tearing/crushing action, and when fully opened provide a wide gape entrance to the mouth.   No wonder they can chew up their prey so quickly and effectively.

Thanks to a hot, hot day and a 1917 textbook on dragonfly anatomy, I now know a little more about dragonfly faces.