Suborder Zygoptera
damselflies

Damselflies (Zygoptera) belong to the order Odonata. Odonata means "toothed,” and refers to the chewing mandibles of these carnivorous insects. There are two suborders within Odonata: Anisoptera (dragonflies) and Zygoptera (damselflies). Suborder Zygoptera accounts for about one-third of the species in Odonata and comprises 12 recognized families and approximately 95 genera worldwide. ("Odonata (Dragonflies and Damselflies)", 2003; Corbet, 1999; McGavin, 2001; U.S. Department of Agriculture, 2002)

Damselflies are carnivorous insects that live and breed near a wide variety of freshwater habitats. They lay their eggs in water, and the immature damselflies spend the first several months or years as aquatic predators. These immature damselflies, called nymphs, have external gills that allow them to extract oxygen from the water. After undergoing metamorphosis, new adult damselflies fly away from the water for a brief period of several days to several weeks, after which they return to breed. Both adult and immature damselflies are predators whose diet consists primarily of insects. (Corbet, 1999; Silsby, 2001)

Damselflies are native to all regions of the world, with the exception of Antarctica. Tropical regions host the highest diversity of damselfly species. ("Odonata (Dragonflies and Damselflies)", 2003; Silsby, 2001; Westfall and May, 1996)

Because damselflies depend on freshwater for oviposition (egg-laying), their primary habitat requirement is the presence of freshwater. Beyond freshwater, it is not clear what factors influence habitat selection, though the structure of emergent vegetation for oviposition appears to be important. Other factors that might be important include the rate of water flow, water quality (oxygen content, pH, nutrient load), refuge from predators and variability in water level. Each species of damselfly has distinct habitat preferences for each of these variables. For example, damselflies can be found in freshwater habitats from temporary pools to waterfalls, but individual species occupy only habitats within a certain range of water speeds. (Silsby, 2001; Westfall and May, 1996)

Zygoptera is one of two suborders within the order Odonata. The phylogenetic relationship between these two suborders, Zygoptera and Anisoptera (dragonflies), is unclear. In some phylogenies, Anisoptera and Zygoptera are sister taxa. In others, Anisoptera (dragonflies) evolved from within the Zygoptera. (Corbet, 1999; Gullan and Cranston, 2000; McGavin, 2001)

Before 1924, taxonomies often placed damselflies and dragonflies in the order Neuroptera. However, it is now agreed that together they form a separate order, Odonata. (Corbet, 1999; Gullan and Cranston, 2000)

The word Zygoptera means "paired wings," and suggests a key character that distinguishes this group from the closely related Anisoptera ("unlike wings"). Damselflies’ two sets of wings are similar in shape, often with elongate bases. Dragonflies, on the other hand, have two dissimilarly-shaped pairs of wings; the rear pair with a much wider base than the front pair. Other characteristics that distinguish damselflies from dragonflies include a broad (transversely elongate) head with eyes that are widely separated, the closed manner in which the wings are held at rest, four rather than three caudal appendages at the tip of the male abdomen and all females having a functional ovipositor. Slender damselfly larvae, with three caudal gills at the tip of the abdomen, are easily distinguished from dragonfly larvae, which have internal gills and tend to be broad-bodied. (Silsby, 2001; Westfall and May, 1996)

Characters shared between damselflies and dragonflies include two sets of long membranous wings, an elongate, 10-segmented abdomen, secondary genitalia in males, and a fully aquatic nymph stage. (Needleham, Westfall, and May, 2000; Silsby, 2001)

Damselflies are separated into families and genera based primarily on wing venation, color, pattern and structure of the genitalia. However, size, shape and habit can be used to recognize many species in the field. (Borror, Triplehorn, and Johnson, 1989)

Damselflies are long, slender-bodied insects with two pairs of membranous wings. They have broad heads with large, widely separated eyes and inconspicuous bristle-like antennae. The thorax is three-segmented, and skewed in a manner that gives the three spiny pairs of legs the appearance of being thrust forward. The legs form a basket that can be used for scooping prey out of the air. The abdomens of damselflies are very slender, ten-segmented and often brightly colored or distinctly patterned. The color of some species can change with environmental variables, fading from bright blue to dull purple in response to cool temperatures or darkness. Males of most damselfly species are more brightly colored than females. In some species females occur in more than one color phase. Frequently, in these species, one of the female color phases is similar to the coloration of the male. (Borror, Triplehorn, and Johnson, 1989; Silsby, 2001; Westfall and May, 1996)

Immature damselflies, called larvae or nymphs are slender-bodied with a wide head and are cryptically colored in browns and greens. One distinctive feature of damselfly larvae is the modified lower lip (labium), which is called a "mask" because it covers the underside of the head. The mask is long and hinged and armed with a set of grasping, claw-like lobes. When larvae sense prey nearby, they can thrust the mask rapidly forward and grasp prey between the lobes. Damselfly larvae also have three leaf-like gills (also known as caudal lamellae) at the tip of their abdomen, which they used to extract oxygen from the water. These gills are often strikingly patterned and can be useful for identifying nymphs. ("Odonata (Dragonflies and Damselflies)", 2003; McGavin, 2001; Silsby, 2001)

Though at first glance, damselflies appear to be very similar to dragonflies, there are several characters that distinguish the two groups. Damselflies have two pairs of wings that are similar in shape and are held closed when at rest. The rear wings of dragonflies have a much broader base than the front wings, and both pairs are held horizontally at rest. Damselflies have a broad head with eyes that are separated by more than the width of an eye, as opposed to a round head with closely placed eyes. Males have four rather than three caudal appendages at the tip of the abdomen and all females have a functional ovipositor. Damselfly larvae are slender, with three external caudal gills at the tip of the abdomen. This distinguishes them from dragonfly larvae, which have internal gills and tend to be broad-bodied. (Silsby, 2001; Westfall and May, 1996)

The smallest known damselfly is the southeast Asian species, Agriocnemis femina. This petite damselfly has a wingspan of only 20mm. The largest known species of damselfly, in the genus Mecistogaster, has a wingspan of 200 mm. ("Odonata (Dragonflies and Damselflies)", 2003; Silsby, 2001)

There are three stages in the damselfly lifecycle: egg, larva and adult. Eggs are laid in water and usually hatch after one to three weeks. The length of this period varies between and within species. Some eggs that are laid late in the summer may even overwinter before hatching. After hatching from the egg, the larval damselfly, also called a nymph, lives in water as an aquatic predator. Damselflies live for two months to three years as nymphs, undergoing 5 to 15 molts as they grow. The length of the nymphal stage varies between species and within species, and depends on temperature, food supply and photoperiodic regime. During the last larval instars, the nymph begins to develop some of the features that will prepare it for life as an adult, such as expanded eyes, flight muscles and wings. ("Odonata (Dragonflies and Damselflies)", 2003; Westfall and May, 1996)

When a damselfly nymph is nearly adult size, it crawls out of the water onto a plant stem or other substrate, and the new adult emerges from the nymphal exoskeleton. The new adult then flies away from the water, and remains away for two or more weeks. During this time, the damselfly eats voraciously (they emerge from the water with very little stored energy) while the exoskeleton hardens and develops the characteristic color and pattern of the adult and the gonads of the young insect mature. Once the adult is fully mature, it returns to an area near water to breed. In many species, this is the likely to be the same habitat where the nymph emerged from the water. Other species range more widely, and young adults may disperse to new breeding sites. (Borror, Triplehorn, and Johnson, 1989; Corbet, 1999; Silsby, 2001; Westfall and May, 1996)

The lifespans of damselflies vary by species. The average damselfly probably lives for three to four weeks as an adult. However, there is quite a bit of variability between and within species. Once in the adult stage, some species survive for a few weeks and some for several months. The amount of time that damselfly nymphs spend in the aquatic stage can range from weeks to years, depending on the species, temperature, food availability and photoperiodic regime. In general, tropical species spend less time in the aquatic stage and more time in the adult stage than temperate species. (Borror, Triplehorn, and Johnson, 1989; Silsby, 2001; Westfall and May, 1996)

Sources of dragonfly mortality are not well studied, but are thought to include predation, chilling, injury, starvation and parasites. (Westfall and May, 1996)

Most species of damselflies (and dragonflies) require a minimum temperature in order to fly. Despite being exothermic, they can control their body temperature to some extent by stretching out in the sun to warm up and by adjusting their orientation to the sun (tipping abdomen up) to control the amount of solar radiation they absorb. Because of this temperature limitation, most species of damselflies are diurnal. Damselflies are very agile fliers. Like the other Odonates, damselflies can control the frequency, amplitude and angle of their two sets of wings independently. Though the two pairs of wings typically beat out of phase with one another, damselflies can control them independently, and can even move all four wings at different frequencies. Despite this, damselflies do not fly with the speed and agility of their close relatives, the dragonflies. Damselflies can fly on average, about 10 km/h, whereas some species of dragonflies can fly at speeds greater than 70 km/h. (McGavin, 2001; Silsby, 2001; Westfall and May, 1996)

Damselflies are solitary creatures. Social behaviors such as swarm feeding are rare in damselflies. (Silsby, 2001)

Damselflies primarily use sight to interact with their environment and with one another. Their large eyes afford them excellent vision compared to most insects. Therefore, visual cues play an important role in communication and perception. For example, males display vivid patterns and colors on their wings, face, abdomen or legs to signal their prowess to both rival males and potential mates. Damselflies hunt visually, sighting prey from a perch before flying after them. There is evidence that damselflies can see ultraviolet light, which may provide additional visual cues that can't be seen by humans. However, the vision of damselflies is not as acute as that of dragonflies, which may account for their slower flight speed. (Silsby, 2001; Westfall and May, 1996)

Damselflies also use mechanical and chemical cues to sense and their environment. Antennal mechanoreceptors allow them to gauge flight speed and mechanoreceptors at the base of the wings gauge and control wing twisting. Also, chemical and mechanical cues are probably used in communication between mating pairs and in selection of oviposition sites. Early instars of damselfly nymphs use primarily tactile cues to detect prey and predators. As their eyes develop in later instars, vision become more important for hunting and sensing predators. (Corbet, 1999; McGavin, 2001; Westfall and May, 1996)

Damselflies are solitary, opportunistic predators. They are primarily insectivores, but will eat nearly anything that they can successfully catch and ingest. This means that they eat primarily aerial prey. Damselflies have three pairs of legs with spiny bristles that interlock to form a basket. The legs are tilted forward, so that the basket can be used to scoop prey out of the air while in flight. The short front pair of legs allow the insect to feed while flying. In general, damselflies are not active hunters. They typically hunt from a perch and ambush prey as they come into view. This strategy conserves energy and may make the dragonflies less vulnerable to predation. (McGavin, 2000; Silsby, 2001)

Adults primarily eat flying insects, such as flies, mosquitoes and moths and butterflies. They also eat beetles and caterpillars. A few species of damselflies have more specialized diets. For example, one South American species plucks spiders and/or their prey out of spiderwebs. (Silsby, 2001; Westfall and May, 1996)

Damselfly nymphs are also predators that employ a “sit and wait” strategy. They rest, hidden in vegetation, and wait for prey to come within striking distance. However, if the supply of prey is not sufficient, nymphs will take a more active approach, either moving to a new hiding place or actively swimming in search of prey. Some damselfly larvae are territorial, and defend temporary feeding sites. These larvae use their gills to perform aggressive displays to defend their territory. Damselfly nymphs will eat most moving organisms that they can catch, including fry fish, tadpoles, water beetles, and even smaller Odonate nymphs. (Gullan and Cranston, 2000; McGavin, 2001; Silsby, 2001; Westfall and May, 1996)

Damselfly nymphs are vulnerable to predation by a number of aquatic predators, including fish, water bugs, beetles and larger damselfly and dragonfly larvae. When threatened, damselfly nymphs either conceal themselves among vegetation, or swim by undulating their bodies and using their gills like a tail fin. (McGavin, 2001)

Predators of adult damselflies include fish, birds such as swallows and martins, frogs, rodents, small mammals, lizards, spiders, small bees and wasps, larger species of dragonflies and damselflies and insect eating plants such as sundew. Damselflies are agile fliers, and primarily use flight to escape predation. (Silsby, 2001; Westfall and May, 1996)

Damselflies prey on a wide variety of species. However, their effect on prey populations is thought to be small. They also serve as food for many aquatic and terrestrial predators. (McGavin, 2001; Westfall and May, 1996)

Damselfly nymphs and adults can be hosts to several species of trematodes and larval water mites. The small, reddish mite larvae attach themselves to the aquatic nymph, and then to the adult damselfly when it emerges. They feed on the damselfly’s blood for two or three weeks, and eventually leave it to return to the water where they develop into adult mites. The mites do not appear to cause significant harm to their host, though especially heavy infestations can lower the number of eggs a female is able to lay and/or eventually kill an adult. (Borror, Triplehorn, and Johnson, 1989; Corbet, 1999)

There are few known adverse affects of damselflies on humans. Contrary to popular belief, adult damselflies do not bite or sting. (Corbet, 1999)

Damselflies are valuable indicators of environmental quality. Because they are found in a wide variety of aquatic habitats and many species have specific tolerances to environmental disturbance, population levels may be a useful measure of ecosystem health. ("Odonata (Dragonflies and Damselflies)", 2003; McGavin, 2001; Westfall and May, 1996)

The destruction and alteration of freshwater habitats is the greatest threat to damselfly species worldwide. Without clean water and appropriate oviposition sites, damselflies are unable to breed. Causes of pollution and/or destruction of freshwater habitats include human development for agriculture, industry and housing, agricultural and industrial pollution, alteration of streamflow for irrigation, and destruction of streambanks and shoreline by livestock. Alteration of habitat through global warming may also pose a threat to damselfly populations in the future. (Silsby, 2001; Westfall and May, 1996)