Adult boreal bluets are 28 to 36.6 mm long, with a hind wingspan of 17 to 22 mm. Due to their ovaries, females weigh more, at about 46.0 mg, while males weigh about 32.6 mg. Their bodies are mostly blue and black. Males have a blue face, while the back of their head is yellowish or pale blue. Their pronotum (first part of the thorax after the head) is black; their thorax is blue and fades to cream. Their legs are blue or tan with black stripes. Their abdomen is bright blue, with pale blue or yellow on the sides, and black markings and 3 short dark bands, followed by 2 long dark bands. The appendages on their rear are black and rounded. Females are polymorphic, meaning they have forms that can look completely different from each other; in this case, they have 2 forms. One female form has the same coloration and markings as the male, while the other is tan, yellowish-green, or pale blue. Their head and thorax are similar to males, though their legs have fewer black markings. Their abdomen is mostly dark, with significant light areas near the end. During the teneral stage, when adult damselflies are not yet able to mate, their wings have a rainbow sheen, and their body is soft and colored grey or brown. Mating adults have brightly colored, firm bodies and clear wings. Larvae are aquatic; they have long, thin bodies with gills, and are usually brown or greenish. Larvae have a large lower lip (labium) that they shoot out to catch prey. The oldest larval stage has wing pads. The gills are usually pale, and much longer than broad. Their eyes are prominent, and their abdomen is covered with hair. Bluet dragonflies all look very similar, and many species can only be told apart by using a microscope to look at the appendages on the ends of the males, and certain plates behind the pronotum of the females. These parts are unique on each species. (Acorn, 2004; Anholt, et al., 1991; Forbes, 1991; Glotzhober and McShaffrey, 2002; Hecker, et al., 2002; Walker, 1944; Westfall Jr. and May, 1996)
Boreal bluets (Enallagma boreale) are damselflies native to the Nearctic region. They live in northern North America, from coast to coast in Canada and the United States. In Canada, they are common 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 live as far south as Virginia in the east, and Arizona and New Mexico in the west. (Duffy and Liston, 1985; Westfall Jr. and May, 1996)
Larvae of boreal bluets are aquatic, and can be found in slow streams, ponds, small lakes, and semi-permanent ponds. They are a freshwater species, though they can tolerate both saltier water and alkaline (basic) conditions. Adults live on land, typically near the bodies of water from which they emerged. These bodies of water are found in woodlands, peatland bogs, marshes, and in the mountains. (Beirinckx, et al., 2006; Duffy and Liston, 1985; Glotzhober and McShaffrey, 2002; Paulson, 2011; Rivard, et al., 1975; Scultz, 2009; Westfall Jr. and May, 1996)
Boreal bluets go through incomplete metamorphosis, and have egg, larva, and adult lifestages. Adults emerge in the summer, and mate and oviposit eggs in bodies of water, then die shortly after. Egg hatching time depends on the water temperature, 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 stages, called instars; larvae reach the later instars by October. As temperatures drop and winter approaches, the larvae go into hiding for the winter (called overwintering). Larvae are able to survive in water temperatures as low as -4° C. They resume activity in mid-April, and molt and emerge from the water as tenerals, which are adults that are not yet ready to mate. This stage lasts 4 days to several weeks, during which, tenerals fly and feed constantly. Female tenerals take longer to develop since their eggs need to develop. Typically one generation is produced each year, but in some populations, larvae overwinter for two winters. This is likely in colder regions, where larvae resume activity later in the season due to cold water temperatures and are not able to complete development to adulthood in time. (Acorn, 2004; Baker and Clifford, 1982; Beirinckx, et al., 2006; Duffy and Liston, 1985; McPeek and Peckarsky, 1998; Rivard, et al., 1975; Scultz, 2009)
For boreal bluets, mating takes place during the summer, typically from June to July, though in warmer regions it can begin as early as May and end as late as September. Males tend to spend much of their time near the breeding site, at the edge of lakes or ponds, while females forage farther away while they mature batches of eggs. When females are ready to mate, they return to the breeding site. Males use the end of their abdomen to grasp the females by the plate behind their head. They fly together, and then typically land on vegetation to mate. Boreal bluets are polygynandrous, meaning both males and females can mate many times with different mates, though they usually do not mate more than once a day. There has been much discussion about why there are two different colors of females. Some researchers have thought the reason some females look like males is because it prevents the males from bothering them, since males think they are also males, they will not try to mate with them. However, this would mean these females never mate, or produce offspring. This does not seem to be the case, though, as males still mate with females that resemble males, so researchers are still not sure why these two different types of females exist. (Beirinckx, et al., 2006; Forbes, 1991; Glotzhober and McShaffrey, 2002; Miller and Fincke, 1999; Paulson, 2011; Rivard, et al., 1975)
Egg laying usually occurs while the male and female are still flying together, though sometimes females lay their eggs alone. After mating, the pair spends several minutes searching for a suitable site, and then up to an hour laying eggs on the surface or underwater, often on leaves or plant stems. Each female has clutches of almost 400 eggs. Females lay multiple batches, with time between each mating to mature the next batch of eggs within their ovaries. While doing so, females leave the breeding site and go to areas farther from water where there are fewer males. (Anholt, 1994; Glotzhober and McShaffrey, 2002; Rivard, et al., 1975)
Adult boreal bluets provide nutrients in the eggs to help the offspring grow and develop, and lay the eggs in an aquatic habitat where they can successfully hatch and the larvae can thrive. Otherwise, adults provide no parental care. (Rivard, et al., 1975)
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. (Paulson, 2011)
Adults fly and forage for food less in rain and strong wings. With large wings and small bodies, bad weather makes flying difficult. When bad weather approaches, boreal bluets leave their pond or lake and take cover in vegetation. They can likely sense the drop in temperature and the decrease in light as clouds move in, but this may just seem like nightfall, causing them to return to their night roosts. They are active during the day, and spend the night in vegetation. Males and females have different foraging styles. Females spend more time away from the body of water where they emerged, to avoid unwanted male attention while a new batch of eggs matures. Males spend less time foraging and stay closer to the water, since they do not have to develop eggs; they do not need as much energy. Males do not defend their territory, and adults are solitary except when mating. Larvae hunt by sitting and waiting for prey to swim by, and then they use their large lower lip to snatch the prey out of the water. They are largely solitary, though some species have territorial larvae, although this does seem to be the case among boreal bluets. When necessary, they can use their gills to swim faster. (Anholt, et al., 1991; Coughlan, et al., 1985; Westfall Jr. and May, 1996)
Adults stay near the ponds and lakes where they emerge, though females are more likely to travel farther than males. (Beirinckx, et al., 2006)
Vision is an important sense for damselflies. The amount of sunlight can be used as a behavioral cue; if sunlight decreases, nightfall or a storm may be approaching, signaling to the 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 set far apart on their heads. 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 the end of his abdomen to fly together. If their parts do not fit together, which happens if a male tries to mate with a different damselfly species, the pair will not be able to mate. Larvae use their antennae to find prey by feeling it as it moves nearby. Older larvae also use sight to hunt. (Paulson, 2011; Westfall Jr. and May, 1996)
Adults are insect predators. Much of their prey are flying insects, such as small flies, mayflies, and smaller dragonflies and damselflies. They can also grab insects such as aphids off of plants. Larvae are also predatory, and sit and wait for prey to swim by, before they shoot out their lower lip and snatch the prey. They feed on zooplankton (Daphnia), as well as other aquatic insects and organisms, including other damselfly and dragonfly larvae. (Coughlan, et al., 1985; Duffy and Liston, 1985; Paulson, 2011)
Boreal bluets do not usually live or lay eggs in waters populated by fish, when they do fish from family Centrarchidae prey on their larvae. By only living near water without fish, their larvae and adults are much safer. In fish-less habitats, dragonflies are usually the top predator, and both adults and larvae prey on larval and adult 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, lining their bodies up with the stem. By staying on the opposite side of the stem, they can hide from predators. Larvae are preyed upon by frogs and aquatic insects, although their green or brown coloration acts as camouflage. Cannibalism is also a threat, as larger larvae preys on smaller larvae and eggs. (McGuffin, et al., 2006; McPeek and Peckarsky, 1998; Paulson, 2011; Westfall Jr. and May, 1996; Wisenden, et al., 1997)
Boreal bluets prey on many insects, and also serve as prey to other insect species, as well as larger animals like birds and frogs. Boreal bluets can host one stage of frog lung flukes (Haematoloechus longiplexus). They can also host parasitic gregarines (Apicomplexa: Eugregarinidae), which can live in their digestive system, though these parasites seem to cause minimal damage. Boreal bluets live in the same area as many other bluet damselflies. Interestingly, boreal bluets are never found in the same area as northern bluets despite being almost identical in appearance, and having very similar ecology. No one knows why they separate when they are so similar. (Acorn, 2004; Hecker, et al., 2002; Novak and Goater, 2013; Paulson, 2011)
There are no known negative effects of boreal bluets on humans.
There are no known positive effects of boreal bluets on humans.
Boreal bluets are not an endangered species.
Angela Miner (author), Animal Diversity Web Staff, Leila Siciliano Martina (editor), Animal Diversity Web Staff.
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