Natural Notes: Dragonflies and Damselflies

The following blog post consists of my notes from a lecture titled "Odanata and Forest Ecology" held at Crabtree Nature Center in Barrington, Illinois in August 2016.  The lecture was delivered by Laura Brown and Nigeen Almassi, naturalists with the Forest Preserves of Cook County.  

Introduction

Dragonflies and Damselflies are a showy group of insects in the taxonomic order Odanata.    The primary differences between Dragonflies (class Anisoptera) and Damselflies (class Zygoptera) are their overall size (dragonflies are usually larger), the position of their wings at rest (dragonflies hold them out while damselflies usually hold them over their abdomen), the thickness of their abdomens (dragonfly abdomens are usually thicker), and their hunting habits (dragonflies are strong fliers and damselflies gently glean prey from vegetation or the water's surface).  Most damselfly wings are clear while some species, such as the Ebony Jewelwing, have colored wings.  Table 1 outlines the key differences between dragonflies and damselflies.

Table 1:  Dragonflies vs. Damselflies

Dragonflies	Damselflies
Wings open at rest	Wings usually held together over abdomen
Thicker abdomen	Thinner abdomen
Larger, stronger fliers	Hunts by gleaning on water or vegetation

Life Cycle and Role in Aquatic Ecosystem
Odonates undergo incomplete metamorphosis (figure 1).  Eggs are laid directly into the water and hatch as an aquatic nymph.  Nymphs develop via a series of aquatic instars before molting into an air-breathing adult that looks much different than the nymph.

Figure 1:  Odonata life cycle

Odonates spend most of their life in the aquatic nymph stage.  Nymphs, shown in figure 2, hatch out of the egg underneath the water ready to feed on small insects.  Nymphs are fierce predators that use a claw-like labium to catch prey (see figure 3) and are opportunistic predators.

Figure 2:  Damselfly vs. Dragonfly nymphs

Figure 3:  Labium

Nymphs will climb onto shore or onto emergent vegetation to finish their life cycle.  As adults they can control the motions of each wing separately, which allows them to make a quick directional change with control.  Nymphs will leave behind a shedded exoskeleton known as an exuvia  (pl. exuviae) which can often be found in large numbers under rocks or tree roots near water. 

If an adult has shiny wings, do not pick it up or attempt to catch it!  Newly emerged wings can be easily damaged.  Adults need to eat for energy in order to reproduce.  Dragonflies bite heads off of prey to prevent them from biting back.  

Sexual Reproduction

Odonate sexes can be distinguished by their reproductive structures on their abdomens.  Females have an ovipositor on their abdomen for dispersing eggs.  Males have parapracts on their secondary genitalia that they use to grip the female.  Figure 4 shows the main anatomical differences between male and female odonate abdomens.  Males will often scrape out the proceeding males sperm during copulation  Copulation can last from a few minutes to several hours (see "mating wheel" in figure 5) with ovipositing occurring shortly thereafter.  

Figure 4:  Male vs. female abdominal reproductive parts.

Figure 5:  Dragonfly "mating wheel".

The primary genitalia for a male is known as the humulus, and can be found underneath the eggs their the joint between the abdomen and the thorax (figure 6).  

Figure 6:  Male abdomen.  Take note of humulus (accessory genitalia).

Habitats

Odonates are widely dispersed in multiple types of habitats such as ponds, streams, lakes, etc.  Nymphs from some species can survive poor water quality with low dissolved oxygen and pollutants.  Some species migrate as adults.  

Common Species

The following are some common species that can be found in Illinois.  

Green Darner (Anax junius).  Green darners are a large and showy dragonfly, although they only spend their life as an adult for a few short weeks!  They stay up to 4 years as aquatic nymphs.  Green darner females lay their eggs on lakes, ponds, and slow moving streams with lots of vegetation.  Adults can migrate.  

Black Saddlebags (Trema lacerata).  Adults migrate.  Females lay their eggs in flooded ditches or other fishless bodies of water.  Fishless areas are required for successful development.  

Blue Dasher (Pachydiplax longipennis). Females lay their eggs in still water.  They oviposit directly onto submerged vegetation, and nymphs can tolerate low dissolved oxygen and pollutants.  

Eastern Forktail (Ishnura verticalis).  This species inhabits ponds, lakes, and slow-moving streams.  Females mate only once, laying over a thousand eggs.  Eastern forktail adults are low fliers, flying short distances from grass to grass or stem to stem.  

Familiar Bluet (Enallagma civile).  Bluets are widely distributed and colonize new and temporary aquatic habitats.  Eggs are laid in roots, stems, and leaves at the surface of the water.  

Narrowly Defined Habitats

The following are some more habitat-specific species.  

Springwater Dancer (Argia plana).  This species was discovered in Cook County in 2010 at Bluff Spring Fen at the Sagawau Environmental Learning Center within the landholdings of the Forest Preserves of Cook County. This record is the furthest eastern record.  Its breeding habitat is small, shallow springs and seeps with a clay bottom.  Females lay eggs on or in clay of a stream, but they have also been observed to lay eggs in aquatic plants.  Wings are generally longer than similar-looking bluets and are about as long as the abdomen.  Bluets have shorter wings.  

Ebony Jewelwing (Calopleryx maculata).  Their breeding habitat is small streams with ample canopy cover.  

Arrowhead Spiketail (Cordulesaster obliqua).  The breeding habitat for this species is small, forested streams.  

Hine's Emerald (Somatochlora hineana).  The breeding habitat for this species is fens and seepage sedge meadows as well as intermittent streams.  Females lay eggs directly into shallow water.  Nymphs survive the winter by taking refuge in crayfish burrows.  Hine's Emerald dragonflies are state and federally endangered.  

Elfin Skimmer (Nannothemis bella).  The breeding habitat for this species is bogs and fens.  Females will perch close to sphagnum moss or on sedges and lay their eggs on water or on the sphagnum moss.  The adults look similar to a wasp or yellowjacket.