- Scientific name: Enallagma minusculum
Species of Greatest Conservation Need (MA State Wildlife Action Plan)
Description
Male little bluet
The little bluet is a small, semi-aquatic insect of the order Odonata, suborder Zygoptera (the damselflies), and family Coenagrionidae (pond damsels). Like most damselflies, little bluets have large eyes on the sides of the head, short antennae, and four heavily veined wings that are held folded together over the back. The male’s thorax (winged and legged section behind the head) is blue with black dorsal and shoulder stripes. The blue on the thorax becomes lavender with age. The species has a long, slender abdomen, which is composed of ten segments and is about equally black and blue. The abdominal segments are blue with an increasing amount of black distally through segment 7. Segments 8 and 9 are entirely blue. The top of segment 10 is black. Females are paler blue or brown than males on the thorax with black abdomen dorsally (Nikula et al. 2007). Adult little bluets range from 24-28mm (0.9-1.1 in) in length making them the smallest species of Enallagma (Lam 2004).
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 and May 1996). Male little bluets can be distinguished by their combination of a lavender thorax not present in other Enallagma, small tear-shaped blue postocular spots, and about equal proportions of blue and black on the abdomen. Males lacking purplish thorax may be confused with pine barrens bluet or New England bluet with similar abdominal black and blue markings but lack horizontal stripe on segment 8. Females difficult to distinguish from other bluets (e.g., marsh and Hagen’s bluets) without examining mesostigmal plates.
Life cycle and behavior
Note adult life stage is synonymous with fight period.
Although little has been published on the life history of the little bluet, it is likely similar to other, better-studied species in the genus. All odonates have three life stages: the egg, the 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.
Little bluets have a one-year life cycle. The eggs are laid during the 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, after which the newly emerged adults (tenerals) fly weakly off to upland areas where they spend a week or two feeding and maturing. The young adults are very susceptible to predators, particularly ants and spiders during emergence, and birds during the teneral stage. Mortality is high during these periods. The adults feed on a wide variety of smaller insects.
When mature, adults return to the wetlands. When a male locates a female, he 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 floating and emergent aquatic vegetation, using the ovipositor on the underside of her abdomen to slice into the vegetation and deposit eggs. Although the female occasionally oviposits alone, in most cases the male remains attached to the back of the female’s 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. The little bluet flight season ranges from late May into August with most observations in June and July.
Distribution and abundance
The little bluet is a regional endemic that occurs in scattered locations in the northeastern United States from New Jersey into Maine and into New Brunswick, Nova Scotia, and Prince Edward’s Island. In Massachusetts, the species occurs in the Millers, Chicopee, Nashua, Concord, Blackstone, Neponset, Taunton, and Cape Cod watersheds. Most observations are from the southeast and can be locally abundant. Few observations occur in the central and western parts of the state but may occur elsewhere.
Distribution in Massachusetts.
1999-2024
Based on records in iNaturalist, Odonata Central, and Natural Heritage databases.
Habitat
Little bluets have been found in a variety of lentic habitats with sparse to moderate levels of emergent and floating vegetation. Occupied wetlands include impoundments and coastal plain ponds where they are most common in Massachusetts. Often, these waterbodies contain sparse to moderate levels of emergent vegetation, including pipewort (Eriocaulon), rushes, and sedges, with sandy to gravelly substrates. The nymphs are aquatic and live among aquatic vegetation and debris. The adults inhabit emergent vegetation in wetlands and fields and forest near wetlands and are negatively associated with shoreline development (Hunt 2020).
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Coastal plain pond shoreline habitat dominated by graminoid emergent vegetation.
Threats
The major threats to little 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 little bluet including graminoid and floating-leaved vegetation. Invasive species including Phragmites can replace native vegetation creating unsuitable habitat conditions for little 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. Since this species occasionally occupies impoundments, unmanaged dam removals may locally extirpate the species from sudden dewatering and habitat loss. 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 little 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 (Hunt et al. 2020).
Conservation
Survey and monitoring
Since little bluet is a regional endemic species and has clear association with relatively intact undisturbed shoreline habitat, tracking this species remains important for species and habitat conservation. Further, little bluet seems to prefer littoral habitat that deviates from other northeastern endemic Enallagma species and warrants continued attention. This species should be recorded when targeting associated state-listed damselfly species including E. pictum, E. recurvatum, and E. daeckii. Standardized surveys should target known sites and new wetlands to determine little 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, open-water, and riparian 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. Effort should also be devoted to surveys at potential suitable sites to document potential range expansion (e.g., western Massachusetts) 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 little 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; prevention and management of nonnative aquatic vegetation; development of best practices for herbicide use; limitation and enforcement of off-road vehicles on shoreline habitat; management of dam removals to mitigate for potential habitat and population loss; and connection 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 pond complexes is needed in Massachusetts to prioritize site conservation. Other needed 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
Brown, V.A. 2020. Dragonflies and Damselflies of Rhode Island. Rhode Island Division of Fish and Wildlife, Department of Environmental Management, West Kingston RI.
Hunt, P. 2020. Conservation planning for endemic damselflies of the northeast: A report to the Sarah K. deCoizart Article TENTH Perpetual Charitable Trust. Concord, NH. 18 p.
Hunt, P., V. Brown, R. Butler, P. deMaynadier, L. Harper, L. Saucier, R. Somes, E. White. 2020. A conservation plan for the endemic damselflies of the northeast. 20 p.
Lam, E. 2004. Damselflies of the northeast. Biodiversity Books, Forest Hills, New York, 96 p.
Nikula, B. 2019. A survey for five species of Enallagma (Bluet) damselflies in southeastern Massachusetts. Report to Natural Heritage and Endangered Species Program, Massachusetts Division of Fisheries and Wildlife, Westborough, MA.
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.
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 7, 2025 |
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