Illinois Natural History Survey - University of Illinois

The Endangered Hine's Emerald Dragonfly

The Hine's emerald dragonfly is the only federally endangered dragonfly species in the United States. The species occupies wetland marshes and sedge meadows fed by shallow groundwater. Like many endangered species, the major reason for its endangered status is habitat loss. Wetland loss is widespread in the United States and in Illinois over 90% of wetland acreage has been lost. Populations of Hine's emerald dragonflies survive in some of the remaining wetlands in Illinois, Wisconsin, Missouri, and Michigan, while the historical range is believed to cover a much larger and more continuous area. The majority of what is known about the Hine's emerald dragonfly's habitat requirements, behavior, and ecology has followed its listing as an endangered species in 1995. Larval habitat use has been studied intensively; however, adult habitat use has proven to be more challenging. The adults are fast fliers and difficult to capture. Studies have shown a male bias in the adult sex ratio and there is limited information on female activity patterns and distribution. Our current research has provided a better understanding of female distribution that contributes to our knowledge of habitat use.

Larval monitoring in Illinois and Wisconsin has shown that the larvae spend two to four years in the aquatic habitat, avoiding predation from crayfish and periods of drought. The lucky survivors crawl out of the water onto emergent vegetation and break out of their larval skins, or exuvia. Exuvia are left behind by the emerging dragonfly and the careful observer can find these skins and determine useful information about the ecology of the species at this stage. Our recent research has suggested an equal number of males and females at emergence despite high male biases in the adult stage.


The adult stage can last several days to several weeks. During the adult stage, males patrol temporary territories in the wetland habitat and females must come into the habitat to lay their eggs. Adults feed on small aerial insect prey in the wetland, in dry meadows, along lakeshores, and in forest clearings. Previous adult studies by researchers at both the Illinois Natural History Survey and the Illinois State Museum have reported a high male bias in the sex ratio. These surveys have, however, been concentrated in the wetland habitat. As a result, it is unknown whether this sex ratio is a reflection of differences in male and female habitat use or higher female mortality rates. Differences in habitat use may result in female avoidance of areas with high male densities and possibly male harassment. Higher female mortality may result from the extra costs associated with producing and carrying eggs. The question is, Where are the female dragonflies? This is a common question in dragonfly biology as well as being an important question when considering conservation of this species.

Knowledge of the adult sex ratio and female habitat use is important for two reasons. First, if males are more abundant than females, the genetic variability will be compromised in later generations. Ultimately, the lack of gene variability will threaten local populations during outbreaks of disease, severe weather, or other environmental stresses. Second, if females are using different habitats than males, then it is critical that both habitats be protected to ensure survival of the Hine's emerald dragonfly.

Last summer adult populations were monitored in wetland and dry meadow habitats to determine if there is a difference in habitat use between males and females. Dragonflies were caught in insect nets and individually marked with bee tags. We determined that the overall adult sex ratio was equal, and differences in male and female habitat use were confirmed. Males were more abundant in the wetland habitats and females were more abundant in the dry habitats. These differences in habitat use may result from male harassment or differences in food availability. Although we observed mating pairs in both habitat types, no male harassment was observed in the dry meadow habitat. Low levels of male harassment limited our ability to make strong arguments for or against this explanation. Insect prey (flies and in particular midges) collected on sticky insect traps were more abundant in the wetland habitats, suggesting that when females avoid these habitats it is not because they have less food. Other untested differences in the habitats may be influencing female distribution patterns.

Whatever the reason for the observed patterns of male and female distribution, sampling in alternative habitats has provided us with a greater understanding of Hine's emerald dragonfly habitat use than exists for most dragonfly species. Populations of males and females occupy a larger area of habitat than wetlands, and both wet and dry habitats are necessary for the survival of this species. This work demonstrates how habitat use by both sexes is an important consideration for species conservation.

Sophie E. Foster and Daniel A. Soluk, Center for Aquatic Ecology

Charlie Warwick, editor


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