Enallagma boreale

Geographic Range

Boreal bluets ( Enallagma boreale ) are a species of damselfly native to the Nearctic region. They are common in northern North America, ranging from coast to coast in Canada and the United States. In Canada, they are widespread in the subarctic, from Nova Scotia to British Columbia, and north into the Yukon and the western mountains. In the United States, they can be found from New England to California, and range as far south as Virginia in the east, and Arizona and New Mexico in the west.

• Biogeographic Regions
• nearctic nearctic
  • native native

Habitat

Their larvae are aquatic, and can be found in lentic habitats, typically slow streams, ponds, small lakes, and semi-permanent ponds. Boreal bluets are a freshwater species, though they can tolerate both saline and alkaline conditions. Adults are terrestrial, and typically can be found near the bodies of water from which they emerged. These bodies of water are located in woodlands, peatland bogs, marshes, and in the mountains.

• Habitat Regions
• temperate temperate
• terrestrial terrestrial
• freshwater freshwater

• Terrestrial Biomes
• forest forest
• mountains mountains

• Aquatic Biomes
• lakes and ponds
• rivers and streams

• Wetlands
• marsh marsh
• bog bog

• Other Habitat Features
• riparian riparian

Physical Description

Adult boreal bluets are 28 to 36.6 mm in length, with a hind wingspan of 17 to 22 mm. Due to their ovaries, females tend to weigh more, at about 46.0 mg, while males weigh about 32.6 mg. Their coloration is primarily blue and black. Males have a blue face, while the back of their head is pale blue or yellowish. Their pronotum is black, and their thorax is blue and fades to cream. Their legs are blue or tan with black stripes. The dorsal side of their abdomen is bright blue, with pale blue or yellow on their lateral sides, and black markings and stripes. There are 3 short dark bands, followed by 2 long dark bands on their abdomen. Their cerci are black and apically rounded in profile. Females can be distinguished by the lack of pits on their pronotum. They are also polymorphic, with two morphs. One female morph shares a close resemblance to males in coloration and markings, while the other is tan, yellowish-green, or pale blue. Their head and thorax are similar to males, though their femora have fewer black markings. Their abdomen is mostly dark, with significant light areas on segments 8, 9 and 10. During the teneral stage, their wings have a rainbow sheen, and their body is soft and grey or brown in color. Sexually mature adults have brightly colored, firm bodies and clear wings. Larvae are aquatic, and have a long, thin body with gills on the posterior end. They are usually greenish or brown. Larvae have a large labium that can extend to catch prey. The labium is long and hinged, so it rests beneath the head and covers the mouthparts at rest. Final instar larvae can be distinguished by their prominent wing pads. Their gills are usually pale, and much longer than they are broad. Their eyes are rather large, and their abdomen is covered in setae. It can be difficult to identify individual Enallagma species, as many bluets must be distinguished microscopically. Boreal bluets are especially similar to northern bluets ( Enallagma cyathigerum ) though they are not found in the same area. Males of Enallagma species have unique terminal appendages, while females have unique mesostigmal plates, located behind and underneath the prothorax.

• Other Physical Features
• ectothermic ectothermic
• heterothermic heterothermic
• bilateral symmetry bilateral symmetry
• polymorphic polymorphic

• Sexual Dimorphism
• sexes colored or patterned differently

Development

Boreal bluets are hemimetabolous. Adults typically emerge in the summer, when they mate and oviposit eggs in bodies of water, then die shortly after. Egg hatching time is water temperature dependent, taking as few as 11 days at 27.5° C to 61 days at 17.5° C. Typically, eggs laid in June hatch in July. There are 5 or 6 larval instars, larvae reach the later instars by October. As temperatures drop and winter approaches, the larvae overwinter. Larvae are able to withstand water temperatures as low as -4° C. They resume activity in mid-April, and molt and emerge from the water as a teneral, a sexually-immature adult. This stage lasts 4 days to several weeks, during which, tenerals fly and feeds constantly. Female tenerals take longer to develop since they have more mass to support in the developing ovaries. Typically one generation is produced each year, but some populations are semivoltine, and larvae overwinter twice. This is likely in colder regions, where larvae resume activity later in the season due to cold water temperatures and cannot complete development in time.

• Development - Life Cycle
• metamorphosis metamorphosis

Reproduction

For boreal bluets, mating occurs during the summer, typically June to July, though in warmer regions it can begin as early as May and end as late as September. Males spend much of their time near the breeding site, at the margin of lakes or ponds, while females forage farther away while they mature batches of oocytes. When females are receptive, they return to the breeding site. Males grasp the females by the mesostigmal plate with their terminal appendages, and fly in tandem. The terminal appendages and mesostigmal plate of each species has unique characteristics, which prevents crossbreeding, as they would not be able to connect and fly in tandem. In males, the genital opening and copulatory organs are separated in the abdomen. The male must transfer his sperm from the end of the abdomen to the seminal vesicle under the second abdominal segment. The female's abdomen must swing forward, with the end making contact with the second segment, where sperm transfer takes place. This is called the "wheel" position. Copulation lasts 23 minutes on average; males usually perch on vegetation and grasp the females. Boreal bluets are polygynandrous, both males and females mate multiple times with different mates, though they likely mate no more than once a day. There has much discussion about the role of female coloration in mating. Pale tan or green females are easily identified, while blue females have been referred to as male mimics. One theory suggests by mimicking males, they avoid harassment from potential male mates. However, this would likely be detrimental to their reproductive success, as males would not select them as mates. This does not seem to be the case, though, as males do mate with them, so they probably should not be considered mimics at all. It is uncertain what purpose the male-similar coloration serves.

• Mating System
• polygynandrous (promiscuous) polygynandrous (promiscuous)

Oviposition usually occurs while the male and female are still flying in tandem, though sometimes females oviposit alone. After mating, the pair spends several minutes searching for an oviposition site, and then up to an hour laying eggs on the surface or underwater, eggs are typically laid on leaves or plant stems. Each female has clutches of almost 400 eggs. Females lay multiple batches, requiring time between each mating to mature their oocytes. While doing so, females leave the breeding site and go to areas farther from water where males are less abundant.

• Key Reproductive Features
• seasonal breeding seasonal breeding
• gonochoric/gonochoristic/dioecious (sexes separate)
• sexual sexual
• fertilization fertilization
  • internal internal
• oviparous oviparous

Boreal bluets provide provisioning in the eggs, and lay them in a suitable aquatic habitat. Otherwise, adults provide no parental care.

• Parental Investment
• pre-hatching/birth
  • provisioning
    • female

Lifespan/Longevity

Development from egg to adulthood can take several months to almost two years in some populations. Adults live 4 days on average, though they can live as long as 17 days.

Behavior

Adult flight and foraging activities tend to be severely impacted by strong winds and rain. With large wings and small bodies, these weather conditions can cause difficulties. If bad weather is approaching, boreal bluets abandon their pond or lake and take cover in vegetation. They can likely detect the drop in temperature and the decrease in light intensity, though this may just mimic nightfall, so they return to their night roosts. They are diurnal, spending the night in vegetation. Males and females forage differently. Females spend more time away from the body of water where they emerged, to avoid unwanted male attention while they mature a new batch of oocytes. They need more energy to develop oocytes, so they spend more time foraging. Males spend less time foraging, as they require less energy, and stay closer to the water. Males are non-territorial, and adults are solitary except when mating. Larvae are sit and wait predators, and are largely solitary. In some species, larvae can be very territorial, but this does not appear to be true for boreal bluets. When necessary, they can use their gills to swim.

• Key Behaviors
• flies
• diurnal diurnal
• motile motile
• sedentary sedentary
• hibernation hibernation
• solitary solitary

Home Range

Adults stay near the ponds and lakes where they emerge, though females are more likely to disperse farther than males.

Communication and Perception

Vision is important for damselflies. The intensity of sunlight can be used as a behavioral cue; if sunlight decreases, nightfall or a storm may be approaching, signaling to adult damselflies that they should take cover in vegetation. They also use their sight to hunt prey, and likely have very good depth perception, as their eyes are spaced widely apart. Color markings and patterns are used as visual cues to identify potential mates. Tactile cues are also used during mating, as the male grasps the female with his terminal appendages to fly together. If their parts do not fit together, if perhaps a male tries to mate with a similar looking yet different bluet species, then the pair will not be able to mate. Adults have mechanoreceptors at the base of the wings, used during flight. Larvae primarily use their antennae to find prey by feeling it as it moves nearby. Later instars also use sight to hunt.

• Communication Channels
• visual visual
• tactile tactile

• Perception Channels
• visual visual
• tactile tactile

Food Habits

Adults are insect predators. Much of their prey are airborne, such as small flies , mayflies , and smaller dragonflies and damselflies . They can also pluck insects such as aphids off of plants. Larvae are also predatory, and sit and wait for prey to swim by, before shooting out their lower lip and snatching the prey. They feed on zooplankton ( Daphnia ), as well as other aquatic insects and organisms, including other Odonata larvae.

• Primary Diet
• carnivore carnivore
  • insectivore insectivore

• Animal Foods
• insects
• zooplankton zooplankton

Predation

On the rare occasion that boreal bluets are found in fish-inhabited waters, the larvae are heavily preyed upon by freshwater fish of family Centrarchidae . However, boreal bluets are almost always found in fish-less habitats. Not only does this eliminate the threat to the larvae, but it also eliminates the threat of fish preying on adults ovipositing in the water. In fish-less riparian habitats, dragonflies are typically the top predator, and both adults and larvae prey on both life stages of boreal bluets. Adult boreal bluets are also preyed upon by birds , spiders , robber flies , and even other damselflies. To defend themselves, adults often perch on plant stems, aligning their bodies with the stem. By staying on the opposite side of the stem, they hide fairly well from predators. Larvae are preyed upon by frogs and aquatic insects. Their green or brown coloration serves as camouflage. Cannibalism is also a threat, as larger larvae prey on smaller larvae and eggs.

• Anti-predator Adaptations
• cryptic cryptic

Ecosystem Roles

Boreal bluets prey on many insects, and also serve as prey to other insect species, as well as vertebrates like birds and frogs. Boreal bluets are second intermediate hosts for frog lung flukes ( Haematoloechus longiplexus ) and can also host parasitic gregarines ( Apicomplexa : Eugregarinidae ), which can live in their midgut, though their effects on the host seem minimal. Boreal bluets have overlapping ranges with many other bluet species. Interestingly, boreal bluets are never found in the same area as northern bluets despite being virtually identical in appearance, and having very similar ecology. No one knows why they separate when they are so similar.

Economic Importance for Humans: Positive

There are no known positive effects of boreal bluets on humans.

Economic Importance for Humans: Negative

There are no known adverse effects of boreal bluets on humans.

Conservation Status

Boreal bluets have no special conservation status.

Additional Links

Encyclopedia of Life

BioKIDS Critter Catalog

Contributors

Angela Miner (author), Animal Diversity Web Staff, Leila Siciliano Martina (editor), Texas State University.

References

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Anholt, B. 1994. Cannibalism and early instar survival in a larval damselfly. Oecologia , 99/1-2: 60-65.

Baker, R., H. Clifford. 1982. Life cycle of an Enallagma boreale Selys population from the boreal forest of Alberta, Canada ( Zygoptera : Coenagrionidae ). Odonatologica , 11/4: 317-322.

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Wisenden, B., D. Chivers, R. Smith. 1997. Learned recognition of predation risk by Enallagma damselfly larvae ( Odonata , Zygoptera ) on the basis of chemical cues. Journal of Chemical Ecology , 23/1: 137-151.