Nature Notes: Dragonflies and Damselflies (Odonata)

by Terry McNamara

Butterflies, flitting about during the summer and spring, are pollinating flowers while feeding themselves. Their bright colors and intricate patterns catch the eye, evoking a sense of beauty in the observer. Members of Odonata—dragonflies and damselflies—also elicit a favorable reaction when viewed by humans. Many have striking metallic or iridescent colors and are admired for their beauty and agile flight. The latter is one of the characteristics that leads to the dragonfly’s reputation as the most efficient predator in the animal kingdom. Recent studies have shown a success rate of 95% in attacks on other insects. They are carnivorous in each of their life stages, taking a heavy toll on mosquitoes, gnats, flies, and other insects.

Their ability to capture prey in mid-air with precision is the result of a combination of physical and mental abilities. They possess large compound eyes that provide binocular vision and capture images at a rate of 200 images per second (IPS). For comparison, human vision maxes out at 60 IPS; an Osprey, at 120 IPS. They can accelerate to more than 30 mph and are able to move in any direction and hover as well. The coordination of their brain, eyes, and wings enables them to single out prey in a swarm with precision. A methodology called camouflage motion used in their aerial pursuits is currently being studied to improve human weapon systems. The hunt ends with a crushing bite to the head or the tearing off of prey’s wings. This is a creature that has evolved into a predator with unparalleled hunting abilities. This makes dragonflies and damselflies important members of our Fishers Island ecological community. Traditionally, these predators have been welcomed into gardens throughout the world. These insects have a direct effect on our mosquito populations and will become even more important allies as the climate changes.

The abundance of ponds and wetlands on Fishers Island provides the habitat critical to the life cycle of these beneficial predators. Unlike butterflies, they do not undergo a full metamorphosis—there is no pupae stage. The eggs laid in a pond or stream hatch into a nymph form called a naiad. This ferocious predatory form has a large, hinged mandible hidden under its head that shoots out and grabs prey. It will grow for two months to five years, feeding on invertebrates like aquatic worms and mosquito larvae, as well as tadpoles and fish. Interestingly, the gills are in the rectum and this positioning enables the nymph to force out a stream of water making it “jet-propelled” when threatened. When ready to take its adult form, the naiad climbs out of the water on a reed or other plant and molts, leaving behind its exoskeleton or exuviae. The adults will then enjoy a brief but brutal predatory period lasting up to four months. During that time, they will also breed and then lay eggs to begin the next generation.

Dragonflies are characterized by large, multifaceted eyes, two pairs of strong, transparent wings, and an elongated body. USFWS photo by Robert H. Burton

Please understand that local spraying of pesticides for mosquitoes or ticks will have a deadly effect on dragonfly populations as well. Additionally, misbeliefs about dragonflies’ ability to inflict harm are unfounded. When handled, a bite can startle and may hurt slightly, but most go unnoticed. The swarms of last summer were most likely caused by the drought conditions, though swarms can occur during concentrated prey insect hatches as well as dragonfly migrations in the fall. They pose no threat to Island residents, as an individual will bite only when threatened. Even then, it’s only a pinch, rarely breaking the skin. Welcome these creatures into your garden where they will feast upon other insects and, in turn, serve as a food source for kestrels, flycatchers, and other bird species.

On Fishers Island, there are usually two periods when the adults emerge from the water, late spring and early summer. We hope to document the presence and emerging times associated with our Odonata population using citizen scientists. Based on data from iNaturalist, Fishers Island Biodiversity Project, and observations of the New York Natural Heritage Program scientists who assessed the Ferguson Museum Land Trust properties, it appears that we have 19 species of dragonflies and damselflies. These lists will be available on the Museum website. Hopefully, they will expand this summer.

We plan to engage an expert entomologist to do a presentation that will provide anyone interested in participating in this project with the skills necessary to identify, photograph and capture Odonata specimens.