- Scientific name: Enallagma carunculatum
- Species of Greatest Conservation Need (MA State Wildlife Action Plan)
- Special Concern (MA Endangered Species Act)
Description
Male tule bluet
The tule bluet is a small, semiaquatic insect of the order Odonata, suborder Zygoptera (the damselflies) and family Coenagrionidae (pond damsels). Like most adult damselflies, the tule bluet has a very long, slender abdomen, large eyes on the sides of the head, short antennae, and four heavily veined wings that are held folded together over the back. On males, the thorax (winged and legged section behind the head) is blue with black stripes on the “shoulders” and top. The abdomen, which is composed of ten segments, is blue with varying black markings on each segment, the black most extensive on the 5th through 8th segments. Females have thicker abdomens than the males, and are generally brown where the males are blue, though older females may become quite blueish. The black abdominal markings are more extensive on females than males. Adult tule bluets range from 26-37 mm (1-1.4 in) in length. Fully developed nymphs are about 19-23 mm (0.75-0.9 in) in length.
The bluets (genus Enallagma) comprise a large group of damselflies, with more than 20 species in Massachusetts. Identification of the various species can be very difficult and often requires close examination of the terminal appendages on the males (Nikula et al. 2007) or the mesostigmal plates (located behind the head) on the females (Westfall & May 1996). The tule bluet is most similar in appearance to the common, widespread familiar bluet (E. civile). The two species are most safely distinguished by the shape of the terminal appendages on the male and the mesostigmal plates of the females. The black abdominal markings on tule bluets are generally more extensive, particularly on the 4th through 6th segments, giving them a darker overall appearance than familiar bluets. However, there is some variation in this feature, and it is not entirely reliable for identification.
Life cycle and behavior
Note adult life stage is synonymous with fight period.
Although little has been published specifically on the life history of the tule bluet, it is likely similar to other, better-studied species in the genus. All odonates have three life stages: egg, aquatic nymph, and flying adult. The nymphs are slender with three leaf-like appendages extending from the end of the body which serve as breathing gills. They have a large, hinged lower jaw which they can extend forward with lightning speed. This feature is used to catch prey, the nymph typically lying in wait until potential prey passes within striking range. They feed on a wide variety of aquatic life, including insects and worms. They spend most of their time clinging to submerged vegetation or other objects, moving infrequently. They transport themselves primarily by walking, but are also capable of swimming with a sinuous, snake-like motion.
Tule bluets have a one-year life cycle. The eggs are laid in late summer and probably hatch in the fall. The nymphs develop over the winter and spring, undergoing several molts. In early to mid-summer the nymphs crawl up on emergent vegetation and begin their transformation into adults. This process, known as emergence, typically takes a couple of hours or less, after which the newly developed adults (tenerals) fly weakly off to upland areas where they spend several days or more feeding and maturing. The young adults are very susceptible to predators, particularly birds, ants, and spiders; mortality is high during this stage of the life cycle. The adults feed on a wide variety of smaller insects which they typically catch in flight.
When mature, the males return to the wetlands where they spend most of their time searching for females. When a male locates a female, the male attempts to grasp her behind the head with the terminal appendages at the end of his abdomen. If the female is receptive, she allows the male to grasp her, then curls the end of her abdomen up to the base of the male’s abdomen where his secondary sexual organs (“hamules”) are located. This coupling results in the heart-shaped tandem formation characteristic of all odonates. This coupling lasts for a few minutes to an hour or more. The pair generally remains stationary during this mating but, amazingly, can fly, albeit weakly, while coupled.
Once mating is complete, the female begins laying eggs (ovipositing) in emergent grasses and rushes, using the ovipositor located on the underside of her abdomen to slice into the vegetation and deposit eggs. Although the female occasionally lays eggs alone, in most cases the male remains attached to the back of the females head. This form of mate-guarding is thought to prevent other males from mating with the female before she completes egg-laying. The adult’s activities are almost exclusively limited to feeding and reproduction, and their life is short, probably averaging only three to four weeks for small damselflies like the tule bluet. The flight period ranges from June to September.
Distribution and abundance
The tule bluet has a wide distribution across Canada and northern and western United States, with records from Nova Scotia and New Brunswick west to British Columbia and south to Maryland, Kansas, and California. It is most common in the western portions of its range. Massachusetts is the species western range edge and occurs in the Hoosic, Housatonic, Farmington, Westfield, Middle Connecticut, and Quinebaug watersheds with most occurrences on and west of the Connecticut River. The species has a scattered distribution in the state. Large populations have been found in the Housatonic watershed pre-2000; however, most sites are observations of a few individuals and may reflect limited survey effort. As such, the status of the species remains uncertain.
The tule bluet is listed as a species of Special Concern in Massachusetts and is protected under the Massachusetts Endangered Species Act (MG.L. c.131A) and its implementing regulations (321 CMR 10.00). As with all species listed in Massachusetts, individuals of the species are protected from take (picking, collecting, killing, etc.) and sale under the Massachusetts Endangered Species Act.
Distribution in Massachusetts.
1999-2024
Based on records in the Natural Heritage Database.
Habitat
Tule bluets inhabit a variety of wetlands but seem to be most numerous on large lakes. In addition to lentic, freshwater habitats, they have also been found on sluggish rivers and apparently are tolerant of brackish conditions. They occur in well-vegetated wetlands as well as at sites where emergent vegetation is sparse. The nymphs are aquatic and live among aquatic vegetation and debris. The adults inhabit emergent vegetation along the shore and nearby uplands. Most Massachusetts sites are sparsely vegetated lakes or reservoirs, though the species also occurs on the Connecticut River.
Healthy habitats are vital for supporting native wildlife and plants. Explore habitats and learn about conservation and restoration in Massachusetts.
Lakeshore habitat with cattail adjacent to a nearby inlet.
Threats
The major threats to tule bluet are shoreline and wetland degradation and loss. Shoreline development may eliminate nearshore/littoral zone and riparian vegetation and harden shorelines through construction of buildings, roads, and other human constructions. Further, shoreline development facilitates increased nutrient and contaminant inputs (e.g., road salts, septic, fertilizer), sedimentation, surface and groundwater withdrawals or water level alteration (e.g., winter drawdown), pesticide use, introduction and spread of invasive species (aquatic vegetation and animals), and recreational activity (e.g., off-road vehicles, boat wakes). These activities lead to wetland/pond degradation that accelerates eutrophication, degrades water quality, and alters or eliminates aquatic vegetation composition required for tule bluet including rushes. Invasive species including Phragmites can replace native emergent vegetation creating unsuitable habitat conditions for tule bluet. In addition, climate change may create unfavorable conditions, including prolonged drought and high-water events, that in combination with ongoing habitat degradation (water withdrawals, nutrient inputs) can increase cyanobacteria blooms, reduce habitat, and alter aquatic vegetation composition unsuitable for the species. High-impact recreational use such as off-road vehicles driving through pond shores, which may destroy breeding and nymphal habitat, and motorboats, whose wakes swamp delicate emerging adults, are also threats. Since tule bluets, spend a period of several days or more away from the pond maturing, it is important to maintain natural upland habitats adjoining the breeding sites for roosting and hunting. Without protected uplands the delicate newly emerged adults are more susceptible to predation and mortality from inclement weather.
Conservation
Survey and monitoring
Standardized surveys should target known sites and new wetlands to determine tule bluet occupancy and population status. Surveys for adults are likely to be more effective for detection compared to nymph or exuvia as this life stage is extremely difficult to find and identify. Adult surveys should target nearshore, riparian, and open water habitats during their flight period during standardized weather and time windows to maximize species detection. Multiple site visits (e.g., ≥3) are likely required to detect this species because of its typical low abundances and ephemerality. Known sites with breeding evidence should be monitored every 5 years or as needed (i.e., in response to extreme conditions like drought) to document changes in occupancy and habitat conditions. Effort should also be devoted to surveys at potential suitable sites to document potential dispersal and update the species distribution and status in the state.
Management
Protection and restoration of shoreline/littoral zone, riparian, and upland habitat is critical for tule bluet persistence in Massachusetts. Actions that can improve or prevent habitat degradation include: reduction of nutrient, agricultural and road runoff; minimization of water level alteration that impacts native aquatic vegetation; minimization of groundwater withdrawals particularly during drought periods; prevent the introduction and manage the spread of nonnative aquatic vegetation species; develop best practices for herbicide use; limit and enforce the use of off-road vehicles on shoreline habitat; and ensure connectivity between ponds and other pond complexes.
Research needs
Research effort is needed to estimate detection and occupancy rates and how other environmental variables (e.g., sample timing, weather) affect these rates. Identification of source and sink wetland sites and general population dynamics within and across coastal plain ponds complexes is needed in Massachusetts to prioritize site conservation. Other research efforts include estimation of physiological tolerances to insecticides and herbicides; impacts of non-native fish and aquatic vegetation on populations; and projections of species distribution under climate change scenarios and climate vulnerability analysis.
References
Lam, E. 2004. Damselflies of the northeast. Biodiversity Books, Forest Hills, New York, 96 p.
Nikula, B., J.L. Ryan, and M.R. Burne. 2007. A Field Guide to the Dragonflies and Damselflies of Massachusetts. Massachusetts Natural Heritage and Endangered Species Program.
Paulson, D. 2011. Dragonflies and damselflies of the east. Princton University Press, Princeton, NJ.
Walker, E.M. 1953. The Odonata of Canada and Alaska, Vol. I. University of Toronto Press.
Westfall, M.J., Jr., and M.L. May. 1996. Damselflies of North America. Scientific Publishers.
Contact
| Date published: | April 3, 2025 |
|---|