Creature Feature: Dragonflies

About 325 million years ago, giant predatory insects of nightmares loomed over the horizon. Some of the coolest (and most terrifying) of them were griffenflies (Order: Meganisoptera) who could have wingspans of over 2 feet [1]! While nightmare-sized bugs like the griffenflies are a thing of the past, their descendants still rule the skies today. In fact, they’re some you’re already familiar with: the dragonflies, which are some  of the most successful predators on the planet [2, 3].

While griffenflies may not exist today, they were voracious predators in the past [Source]

While the term “dragonfly” can refer to any of the nearly 6,000 insects in the order Odonata, it most often refers to the roughly 3,000 species within the suborder Anisoptera (meaning “unequal wings”) that are generally larger and stockier [4]. Here, I use the term dragonfly only to refer to these bigger insects. The remaining  ~2,900 species of more slender insects in the order Odonata form the suborder Zygoptera (meaning “even wings”) and are usually referred to as damselflies [4]. The scientific names for these groups refer to their differences in wing shape; a dragonfly’s hindwings are slightly larger than its front wings, while a damselfly’s fore and hind wings are the same size and shape [1]. Damselflies also have a gap in between their eyes unlike dragonflies, which can make them look a lot cuter too!

While most people associate dragonflies with their colorful flying adult form, they are actually aquatic insects. This means that they spend most of their life in water and only transition to live in the air to reproduce. In the water, a dragonfly is called a “nymph” and looks quite different than its adult counterpart. The wings of a dragonfly nymph are small and still developing in “wing sheaths” on their backs [1]. Thus, they crawl around instead of flying. While they aren’t as colorful or mobile as their adult counterparts, the nymphs do have a few unique tricks up their sleeves, including anal jet propulsion and an extendable labium with clasping hooks on the end [1]! When they need to escape from predators, like big fish or other dragonfly nymphs, the nymphs can eject water from their anus to propel themselves forward and avoid predators or when they’re really hungry, get closer to their prey [1]. In order to grab their prey, including mosquito larvae, tadpoles, or small fish, dragonfly nymphs use their labia to  grab prey with their hooks, much like the xenomorph from the movie Alien. The labia of different dragonfly species varies greatly in size and shape but is about half of their body length, giving them quite the impressive reach to grab their prey [1]. Their success at catching their prey with this unique tool is about 60%, which is very good for a predator [5]!

Before they become the more familiar flying form, dragonfly nymphs go through several developmental periods called instars, during which they shed their skin and grow larger [6]. When a dragonfly nymph completes its final instar (the whole process can take between a few months to a whopping eight years), it climbs out of its watery home, and braces itself to complete its metamorphosis, after which it emerges  as an adult [3]. Newly emerged dragonflies have to dry off and puff out their wings before they can take to the skies [1, 3]. 

A dragonfly emerges after completing metamorphosis [Source].

Adult dragonflies are even more accomplished hunters than their nymph counterparts, having been recorded catching their prey as much as 97% of the time [2]! Most often, they intercept their prey in midair as they move [2]. Dragonfly species tend to hunt their prey in one of two ways: by perching or flying, which dragonfly researchers creatively call perchers and fliers [7]. If you’ve ever seen a big dragonfly in the sky that was constantly on the wing, it was probably a flier. If you’ve seen a dragonfly perching on plants or fences, darting away only to return to the same spot, that’s a percher. Flier species are generally a lot bigger than percher species, and the prey hunted by fliers has a tendency to be larger as well [1, 3]. Some flier species will eat other dragonflies, like the aptly named dragon hunter (Hagenius brevistylus), and on rare occasions, some have even been seen with caught hummingbirds [3]!

But as great of predators as dragonflies are, all good things must come to an end, including their adult life stage. Dragonflies spend the majority of their adult lives eating to gain energy for mating and the competition that can accompany it [3]. For territorial species, like the widow skimmer (Libellula luctuosa), males will chase competitors away in order to capitalize on any females that come looking for mates [1]. Eventually, a male finds a female, and the magic happens. 

After mating, a female dragonfly will deposit her eggs in a water source, usually a stream, pond, or lake [1, 3]. Some species deposit their eggs directly into aquatic plants or even trees! But for territorial species, such as the common green darner (Anax junius), males will continue to guard females after they mate, either by hovering above them or by keeping a hold on the female’s head [1]. Competing males will try to intervene either by trying to grab the female as she lays her eggs or by ramming into the guarding male [1]. Eggs that do get successfully laid soon hatch into nymphs, and  begin the cycle anew. 

An Anax imperator female laying eggs into aquatic plants [Source].

While today’s dragonflies may not look as scary to us as the griffenflies that lived millions of years before them, they are still incredible predators, both in the air and in the water, and deadly to the animals they call prey.


Christofer Brothers is a graduate student in the Animal Behavior Graduate Group at UC Davis. He is interested in the behavior and biomechanics of flying insects, particularly dragonflies and damselflies. He also has an unhealthy love of puns.


References:

[1] Corbet, P. S. (1999). Dragonflies: behaviour and ecology of Odonata. Harley books.

[2] Combes, S. A., Salcedo, M. K., Pandit, M. M., & Iwasaki, J. M. (2013). Capture success and efficiency of dragonflies pursuing different types of prey. Integrative and Comparative Biology53(5), 787-798.

[3] Paulson, D. (2019). Dragonflies and Damselflies-a Natural History. Princeton University Press.

[4] Dijkstra, K-D. B., G. Bechly, S. M. Bybee, R. A. Dow, H. J. Dumont, G. Fleck, R. W. Garrison, M. Hämäläinen, V. J. Kalkman, H. Karube, M. L. May, A. G. Orr, D. R. Paulson, A. C. Rehn, G. Theischinger, J. W. H. Trueman, J. van Tol, N. von Ellenrieder, & J. Ware. 2013. The classification and diversity of dragonflies and damselflies (Odonata). Zootaxa 3703(1): 36-45.

[5] Quenta Herrera, E., Casas, J., Dangles, O., & Pincebourde, S. (2018). Temperature effects on ballistic prey capture by a dragonfly larva. Ecology and evolution, 8(8), 4303-4311.

[6] Byers, C. F. (1927). Notes on some American dragonfly nymphs (Odonata, Anisoptera). Journal of the New York Entomological Society35(1), 65-75.

[7] Corbet, P. S., & May, M. L. (2008). Fliers and perchers among Odonata: dichotomy or multidimensional continuum? A provisional reappraisal. International Journal of Odonatology, 11(2), 155-171.

Main image source

[Edited by Alexandra Dwulit and Meredith Lutz]

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