Hagenius brevistylus

Geographic Range

Hagenius brevistylus , commonly known as the dragonhunter, has a wide distribution across 34 states in the eastern United States and in the adjacent 5 provinces of southeastern Canada. Dragonhunters are endemic, or native and unique, to North America east of the Great Plains.

• Biogeographic Regions
• nearctic nearctic
  • native native

Habitat

Dragonhunters are found in the temperate regions of North America, where adults prefer the banks of forested streams and rivers that have moderate to fast flow. Dragonhunter adults can be found foraging in the woods near streams.

Larvae live in or along the edges of woodland streams, amid leaf litter and detritus, which match their own dark coloration. Older dragonhunter larvae prefer sheltered shorelines with silt-sand sediment bottoms. In the water, larvae are found at depths of 0.5 to 10 m in streams that contain beds of muddy sand and organic debris.

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

• Terrestrial Biomes
• forest forest

• Aquatic Biomes
• rivers and streams

• Other Habitat Features
• riparian riparian

Physical Description

Dragonhunters are large dragonflies that possess long and powerful legs and wings. Adults range in size from 73 to 90 mm long, the span of their hindwings measures 47 to 58 mm, and they weigh an average of 1.2 g.

Adults have green eyes and a small, black head with a face striped in yellow. The body is characterized by black and yellow markings, with two thick, yellow stripes on the sides of the thorax. The dorsal surface of abdominal segments 9 and 10 are completely black, while the rest of the abdomen has yellow spots. The legs are entirely black, with short, heavy spines on the lower sections to assist in taking large prey. The posterior end of the abdomen is enlarged, forming a club. The club of a dragonhunter is relatively small compared to other clubtail dragonflies. The wings are coarse and slightly tinted, with blackish veins running across them.

Males and females are similar in color and markings, but the club on a male is bent downward in a sideways J-shape when in flight or perched. The anal loop (a pattern on the hindwing) is more broad in the female than in the male.

The larvae, or nymphs, of dragonhunters have stilt-like legs and possess a broadly flattened, nearly circular abdomen with serrated edges. These characteristics provide camouflage, as they create an overall resemblance to the dead leaves in which the nymphs hide. The mouth of a dragonhunter larva consists of a pair of heavy ridges to support a stout labium, which is an extendable lower lip that is used to catch prey. At the end of the labium is a pair of palpal lobes lined with hooks, spines, and teeth.

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

• Sexual Dimorphism
• sexes shaped differently

Development

Hagenius brevistylus follows the general pattern of dragonfly development, undergoing incomplete metamorphosis, which does not include a pupal stage. Eggs that are laid late in the summer may undergo diapause, or hibernation, and wait until the spring to hatch. The larval stage of dragonhunters can be exceptionally long, ranging from 4 to 7 years. Larvae appear to be freeze tolerant, which enables them to survive during the winter. The rate at which the nymphs molt and grow depends on ambient temperatures.

• Development - Life Cycle
• metamorphosis metamorphosis
• diapause diapause

Reproduction

Little is known of the Hagenius brevistylus mating system. Like most dragonflies , dragonhunters probably are polygynandrous, such that males and females mate with multiple partners. Little information is available about courtship behavior and mate attraction in dragonhunters. The papillae at the base of the antennae may play a role in courtship and reproduction, but in general, dragonflies depend on vision, and males exhibit territorial behavior to announce availability and suitable egg-laying sites.

Reproduction in dragonflies usually involves two formations between a mating pair: the tandem position and the copulation wheel.

First is the tandem position. Males in the family Gomphidae pursue and quickly grasp females from behind without any apparent behavioral or visual display. The male grasps the female’s head or thorax and curves his abdomen under his body to grip the back of her head with his anal appendages, or claspers. The pair then flies off with the male in the lead, towing the female behind him. This process usually takes less than a second, and at this stage the couple is in the tandem position. The pair stays in this position for seconds to minutes and may fly around in tandem or find a suitable place to settle.

Before mating occurs, the dragonflies in the tandem pair adjust the positions of their bodies to form a copulation wheel. The female curls her abdomen underneath her thorax while in tandem, moving the abdomen forward to contact the genitalia of the male. The couple forms a heart-shaped wheel as the male and female mate. Male dragonhunters use their genital hamuli (small forked appendages) to support the erected penis during mating.

Dragonhunter males are notorious for inflicting severe damage on females while mating. The spines of the male’s anal appendages grasp the female in a vise-like grip, gouging the female’s eyes and usually piercing her head. Copulation is brief, and the couple seldom flies while in tandem, because physical damage can occur. Tandem pairs probably perch in treetops for the majority of the mating interval to prevent linkage strain caused by flying in tandem.

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

The flight and breeding period of Hagenius brevistylus is approximately 3 months in the summer, during which male and female dragonhunters mate as many times as possible. Like most dragonflies , sperm is injected into the female during copulation, but the eggs are not fertilized until they are laid by the female. Males compete for their sperm to be used in fertilization by removing any sperm that previously was deposited in the female before injecting their own.

Dragonhunter females oviposit (lay their eggs) while flying in a zigzag course, circling over a comparatively small area of open water. They rise and descend repeatedly, dipping the tip of their abdomen into the water with each descent to deposit a little cluster of eggs. Information is scarce regarding the number of eggs laid by female dragonhunters, but in most dragonflies , the number varies from a few hundred to a few thousand.

When the eggs of dragonhunters enter the water, they scatter and drift apart as they fall to the bottom. The eggs are evenly covered by a jelly except at the anterior pole, which is left uncovered so that hatching is unhindered. As the eggs fall through the water, silt sticks to their surface, and they become hidden at once. Neither parent protects the eggs after oviposition.

Little information is available about the gestation period of dragonhunters, but most dragonfly eggs hatch within 8 to 30 days, depending on the environmental conditions. Dragonhunter eggs typically hatch during the summer and develop and grow in the water; the hatched larvae shift closer toward the shoreline as they mature. Eggs that are laid late in the summer may undergo diapause, or hibernation, and hatch the following spring.

Parental care has not been observed in this species, and like most dragonflies , H. brevistylus larvae appear to be independent the moment they hatch. The duration of the larval stage in dragonhunters ranges from 4 to 7 years, and the larvae appear to be freeze tolerant, which enables them to survive during the winter. The rate at which the nymphs molt and grow largely depends on ambient temperatures.

Adults emerge after metamorphosis in late June and early July, often on the shoreline, but occasionally as much as a meter high on trees in the forest. Dragonhunters exhibit “mass emergence”, also known as “explosive emergence”, in which most of the annual population appears at once within a short period of time. There is little information on the time of sexual maturity for dragonhunters, but most dragonflies become sexually mature about 2 to 3 weeks after reaching adulthood.

• Key Reproductive Features
• semelparous semelparous
• seasonal breeding seasonal breeding
• gonochoric/gonochoristic/dioecious (sexes separate)
• sexual sexual
• fertilization fertilization
  • internal internal
• oviparous oviparous
• sperm-storing sperm-storing
• delayed fertilization delayed fertilization

As in most dragonflies , yolk from the mother nourishes the hatching larvae. No further parental investment or care is provided by male or female dragonhunters.

• Parental Investment
• no parental involvement
• pre-fertilization
  • provisioning
• pre-hatching/birth
  • provisioning
    • female

Lifespan/Longevity

The lifespan of dragonhunters is about 4 to 7 years. The rate at which the nymphs molt and grow largely depends on ambient temperatures. Adults live no longer than 3 months.

Behavior

Hagenius brevistylus is a relatively solitary species. It is known for its fearlessness, as adults have been observed to relentlessly pursue songbirds that are much larger than the dragonflies themselves.

Dragonhunters display territorial behavior and defend an area vigorously from other individuals of the same species. Little information is available about the size of the guarded territories.

Adults change their orientation with respect to the sun to control their body temperature. For example, at high temperatures, dragonhunters perch with their long abdomens hanging directly downward, parallel to the sun’s rays, thus minimizing their shadow and reducing direct exposure to the sun. Dragonhunters are active when exposed to sunlight.

When hunting, H. brevistylus adults can reach speeds of up to about 40 km per hour. They often attack from above, sometimes knocking prey into water before going in for the kill. Dragonhunters use their long legs to grasp prey and their large mandibles to deliver a powerful and often fatal bite. Adult dragonhunters have a habit of flying along a regular path with definite perches while foraging, and they usually perch to consume large prey. They most often choose to perch on a thorny branch to eat Ebony Jewelwings (a species of broad-winged damselfly) and take approximately 25 minutes to chew and ingest them. When eating monarch butterflies , dragonhunters use their forelegs to rotate the monarch and press the wings of the monarch together for easier handling. Because monarchs sequester unpalatable chemicals in their bodies, dragonhunters avoid eating the more toxic portions of the prey. For instance, dragonhunters almost never eat monarch wings, as the wings contain high levels of toxins. Dragonhunters appear to prefer feeding on monarchs, especially when the butterflies are abundant.

Dragonhunter larvae are slow-moving sprawlers and hiders, as opposed to burrowers; they rest on substrate using their long, extended legs for support. Nymphs occasionally appear near the surface of water to molt. A diverse assortment of larval instars usually can be found together.

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

Home Range

Information is scarce about the home range of dragonhunters. Most evidence suggests that dragonhunter larvae stay within a relatively small area as they mature.

Communication and Perception

Information is scarce regarding the methods of communication and perception specific to Hagenius brevistylus . The papillae at the base of its antennae may be used to communicate with mates, involving touch and chemical signals. Adult dragonflies perceive the environment visually, and they can see UV light. Male dragonhunters are territorial, displaying their size and speed.

Larvae use mechanical, visual, and chemical cues to sense their prey.

• Communication Channels
• visual visual
• tactile tactile
• chemical chemical

• Perception Channels
• visual visual
• ultraviolet
• tactile tactile
• vibrations vibrations
• chemical chemical

Food Habits

Hagenius brevistylus is an insectivore, with adults primarily eating butterflies and other insects, especially other dragonflies . Dragonhunters use their long legs to grasp prey and their large mandibles to deliver a powerful and often fatal bite. Dragonhunters are known to eat Lake Darners , Ebony Jewelwings , Cyrano Darners , swallowtail butterflies , and monarch butterflies . Dragonhunters seem to prefer feeding on monarchs, especially when the butterflies are abundant. Dragonhunters appear able to overcome the toxic defenses of monarchs , bees and wasps .

One experiment concluded that an adult dragonhunter would have to consume 60% of its body weight each day to meet its daily water requirements at 25°C, which would be enough food to power its flight for 4.6 hours. However, due to constraints in the experiment, the calculations may have overestimated the daily requirements.

Larvae are highly predatory and eat anything of suitable size, including other odonate larvae, fish , and amphibians .

• Primary Diet
• carnivore carnivore
  • insectivore insectivore

• Animal Foods
• amphibians
• fish
• insects

Predation

Scarce information is available about the specific predators of dragonhunters. In general, crustaceans , true bugs , beetles , turtles , and waterfowl are predators of dragonfly larvae. Hagenius brevistylus larvae avoid predation mostly by blending in with leaves and detritus in their aquatic habitat.

When transitioning from an aquatic to a terrestrial habitat, and as adults, dragonflies are attacked by ants , spiders , frogs and toads , shrews , raccoons , and various birds .

• Anti-predator Adaptations
• cryptic cryptic

Ecosystem Roles

Dragonhunter larvae are aquatic carnivores and insectivores; dragonhunter adults are aerial insectivores. As major predators of monarch butterflies , Hagenius brevistylus adults can influence monarch behavior. For instance, if dragonhunters are active where monarchs are present, the monarchs avoid predation by feeding in the shade despite their usual preference for sunlight.

Dragonhunters have been affected by the introduction of zebra mussels to the Great Lakes. Because dragonhunter larvae possess a wide abdomen and exhibit sprawling behavior, they are more susceptible to zebra mussel colonization than the slimmer, burrowing larvae of other dragonfly species. The presence of mussels on H. brevistylus larvae has a negative effect on the survivorship of the larvae. Indeed, colonized larvae show decreased mobility and increased susceptibility to predation. However, zebra mussel colonization does not appear to hamper the feeding rate of dragonhunter larvae.

Economic Importance for Humans: Positive

As insectivorous predators, dragonhunters may be effective in regulating insect populations (some of which are pests to humans), such as mayflies , stoneflies , caddisflies , and possibly mosquitoes . Dragonhunters also serve as indicators of clean water in stream ecosystems.

Some research includes Hagenius brevistylus as the study species because it is relatively easy to observe and because of its unique predatory behavior.

• Positive Impacts
• research and education
• controls pest population

Economic Importance for Humans: Negative

There are no known negative impacts of Hagenius brevistylus on humans.

Conservation Status

Dragonhunters are common (though rarely abundant) throughout their geographic range, and their populations are stable. They are present in many federal, state, local, and private reserves and do not require conservation measures at this time.

Additional Links

Encyclopedia of Life

Contributors

Allison Liao (author), University of Michigan-Ann Arbor, Elizabeth Wason (author, editor), Animal Diversity Web Staff.

References

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