The Eye of the Beholder

After three weeks of only sparse sightings of dragonflies, this past week in Terra Nova has been absolutely flooded with these graceful creatures. A few members of the family Aeshnidae seem to be of a particular abundance along the peripheries of the many ponds that punctuate Terra Nova. Green Darners are (relatively) massive with their 3-inch wingspans – they are magnificent flyers, darting through the air with unparalleled precision and speed. Their disproportionately huge eyes process their local environment at a rate I cannot even comprehend. Catching the Green Darner with our nets is typically a challenge given their agility, though with such a large number of them soaring through the air it’s hard not to have one glide into our clutches.

A Shadow Darner, Aeshna umbrosa, found in Ochre Hill Forest, posing for a picture.
A Shadow Darner, Aeshna umbrosa, found in Ochre Hill Forest in Terra Nova National Park, posing for a picture.

I’ve included photos of two of the dragonflies we had encountered while collecting in Terra Nova. In both the photo of the Green Darner and of the Shadow Darner, I am immediately drawn to the spectacular eyes these two creatures possess. Each compound eye is subdivided into approximately 30 thousand individual light-processing units called ommatidia. Each ommatidium contains a cluster of light sensitive cells called photoreceptors, which are responsible for providing a direct visual bridge from the external world of light to the brain. The sum of the 30 thousand individual light processing units weave together an image of the dragonfly’s surroundings. What the resulting final image truly ‘looks’ like to the dragonfly is beyond human comprehension, though this image undoubtedly helps drive the dragonfly’s immense ability to fly.

A Green Darner, Anax junius, the seemingly ubiquitous denizen of Terra Nova.
A Green Darner, Anax junius, the seemingly ubiquitous denizen of Terra Nova NP.

With many who study biology, there is often a common revelation or conclusion to be had: we humans are woefully inept in our sensory abilities compared to some of evolution’s other offerings. The dragonfly, not unlike the mantis shrimp, has the ability to process ultraviolet light in addition to the typical red, green and blue wavelengths that we humans are limited to. The UV light is believed to provide a backdrop against the sky that allows for better resolution and detection of desired prey. In addition to a broader spectrum of visible light for the dragonfly, they also have the benefit of a broader field of view. With their compound eyes bulging outwards into the air, these aerial predators see a lot more than you or I at any given time.


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