Wild Species 2005: chapter 5
Odonata - order of insects that includes the dragonflies and damselflies. They are winged, carnivorous insects with brilliant metallic colouring, whose eggs are laid in water and which develop through an aquatic nymph (larval) stage - Henderson's dictionary of biological terms.
- There are about 6500 species of odonates in the world, of which 209 can be found in Canada.
- The majority (69%) of odonates in Canada have Canada General Status Ranks (Canada ranks) of Secure, while 13% have Canada ranks of May Be At Risk and 13% have Canada ranks of Sensitive. No odonates have Canada ranks of At Risk, because COSEWIC has not yet assessed any odonate species.
- Odonates first emerged over 300 million years ago, about the same time as the reptiles first appeared, making the Odonata one of the oldest orders of insects alive today.
- The fossil dragonfly Meganeura, which lived about 250 million years ago, had a wingspan of over 50 cm, making it the largest odonate known!
- Dragonflies can have more than 25 000 lenses in each eye, giving them almost 360 degree vision.
The order Odonata is divided into three sub-orders, the damselflies or Zygoptera, the dragonflies or Anisoptera, and the Anisozygoptera, which is represented by two living species, both found in Asia. Canada has a total of 209 species of odonates, including 57 species of damselflies and 152 species of dragonflies. All odonates have two pairs of wings, long, slender bodies and large eyes. Dragonflies are usually larger and sturdier than damselflies, and tend to spread their wings horizontally at rest, whereas damselflies hold their wings pressed together over their back or only partly spread. Odonates depend on freshwater for successful reproduction and are found close to freshwater habitats of many different types, from tiny streams to bogs, marshes, fens, swamps and large rivers and lakes.
The odonate life cycle has three distinct phases; egg, larva and adult. Eggs are laid in or close to freshwater and hatch into aquatic larvae, which breathe using gills. The gills of dragonfly larvae are located in the rectal chamber, at the end of the digestive system. By squirting water through their gills, dragonfly larvae can use jet-propulsion to travel through the water. Damselfly larvae are more slender and appear more elegant than dragonfly larvae. They breathe with external gills, which look like feathers extending from the tip of the abdomen. One of the most unusual features of odonate larvae is the large, hinged lower lip, or labium. The labium acts rather like a grappling hook, shooting out at lightning speed to capture prey with dagger-like hooks. This unique capture device allows odonate larvae to be highly successful predators, feeding on a variety of aquatic organisms including other insects and even small fish. Odonate larvae in turn, provide food for an amazing range of animals, from fish and crayfish to birds such as Common Loons (Gavia immer) and juvenile Whooping Cranes (Grus americana).
Depending on the species, odonate larvae live in the water for less than two months to more than five years. When the larva is mature it climbs out of the water, often onto a piece of emergent vegetation. In a dramatic metamorphosis, the larval exoskeleton splits open along the head and the top of the thorax and the adult dragonfly emerges from its larval skin. Once emerged, the adult rests while its wings dry and expand. Then it takes flight for the first time, leaving behind the larval skin or exuvium. After emerging, the adults usually spend a period of days or weeks resting, hunting and gaining weight in upland habitat, before returning to the water to breed. During their time away from the water, adults become sexually mature and their colours often change, becoming brighter and more striking.
Like the larvae, adult odonates are voracious predators, preying on flying insects including mosquitoes, midges and even other odonates. Their success as predators is due to their acute vision and their speed and manoeuvrability in the air. Odonates are extremely well adapted to flying and can catch prey, eat, mate and lay eggs while in flight. Large dragonflies have been reported to reach speeds in excess of 50 km per hour! The adult stage is typically the shortest stage of the life cycle, usually lasting only a few weeks. No Canadian odonates over-winter as adults, but at least two species are migratory.
Odonates breed in a wide variety of aquatic habitats. Their distribution is dependent on a number of factors including acidity of the water, water flow, vegetation, substrate type, competition from other organisms, predation, disturbance and pollution levels. Generalist species, which are able to survive in a variety of habitats, tend to be widely distributed. Specialist species, which have specific habitat requirements, such as the Pygmy Clubtail (Ophiogomphus howei), a species of clear, fast-flowing streams, tend to have sparser, more localized distributions. This can make specialist species vulnerable to population declines, due to habitat disturbance and destruction.
The odonates are a fascinating group of insects that has been attracting increasing attention in recent years from both professionals and amateurs, including children, as demonstrated by the increasing number of scientific and popular publications devoted to odonates. Odonates are both beautiful, and interesting to observe with their complex behaviours and striking colours. There is even a colourful diversity in the intriguing common names of odonates, such as River Jewelwing (Calopteryx aequabilis), Umber Shadowdragon (Neurocordulia obsoleta) and Slaty Skimmer (Libellula incesta). Because odonates are predatory and voracious, and are in turn, important prey items for fish and birds, they play an important role in the ecosystems in which they live. Some species of odonates are sensitive to water quality, potentially making them important environmental indicators.
Status of knowledge in Canada
The odonates are one of our best-known insect groups, but the life history, distribution and habitat requirements of many species of Canadian odonates are poorly understood. Without this basic knowledge, it will be difficult to determine population trends or to prevent population declines or extinctions.
Over the past decade, odonate surveys have greatly improved the knowledge of odonate habitat and distribution in a number of provinces and territories. For example, prior to 1995 the Quebec Emerald (Somatochlora brevicincta) was known only from a few isolated peatlands in Quebec, but has now been found in New Brunswick, Nova Scotia, Newfoundland and Labrador, and British Columbia. This is probably not a recent range expansion; rather, new surveys and a better understanding of its ecology have simply led to its discovery in new locations. Similarly, a recent survey in the Northwest Territories added five species of odonates to the territorial species list.
In the future, systematic surveys, long-term monitoring and focused research projects into biology, life history, threats and other relevant questions will be necessary to improve knowledge of Canadian odonates. This will be particularly important in the north, where odonates are poorly known. Ongoing volunteer projects, such as the Ontario Odonata Survey and Atlas and the Manitoba Dragonfly Survey will be important in providinglong-term information on the distribution and biology of odonates. The results of this general status assessment have aided the Committee on the Status of Endangered Wildlife in Canada (COSEWIC) in prioritising odonate species for detailed COSEWIC status assessments, which will examine the status of some species currently ranked May Be At Risk in greater detail.
Richness and diversity in Canada
Within Canada, Odonate species richness is highest in the eastern provinces, from Nova Scotia to Ontario (Figures 2-4-i and 2-4-ii, Table 2-4-i), particularly in Ontario, where 168 of Canada's 209 species of odonates can be found. Although species richness is lower in the north than in southern Canada, the abundant, pristine wetlands of the north provide widespread and varied habitat for northern specialists, such as the Treeline Emerald (Somatochlora sahlbergi), which is found only in the three territories and in northern Saskatchewan, within Canada. All the odonates known from Canada have also been found in other countries.
Species spotlight - Broadtailed Shadowdragon, Neurocordulia michaeli
Scientists are well aware that the earth's species have not all been discovered or named, but in 1993 a Canadian field biologist reduced the number of species left to be discovered by one. On the Canoose Stream in southwest New Brunswick, Paul-Michael Brunelle came across an exuvium, which he couldn't identify. Exuviae are left behind when a larva metamorphoses into an adult odonate and are useful in identifying odonates. Despite the involvement of several experts, the species still could not be identified. The next year, adult males and females of an unknown species were found in the same location, further deepening the mystery. Finally, in 1996, the unknown adults were seen emerging from the unknown exuviae and it was confirmed that both were of the same, new, species, later named Broadtailed Shadowdragon, Neurocordulia michaeli. An easily overlooked species that flies only at dusk, the Broadtailed Shadowdragon has since been found in Maine, and Ontario, although the Ontario record is not included in Wild Species 2005 as the discovery was made after the odonate rankings were completed in 2003. Broadtailed Shadowdragon has a Canada General Status Rank (Canada rank) of Sensitive.
The opportunity to make new discoveries, such as this, is one aspect that attracts enthusiasts to the study of odonates. New county records of odonates are regularly reported, and new provincial and territorial records are not unusual, but the discovery of a new species is a thrill few people can hope to experience in their lifetime.
Species spotlight - River Jewelwing
Reaching lengths of over 5 cm, the River Jewelwing is one of Canada's largest damselflies, and also one of the most spectacular. The River Jewelwing (Canada rank: Secure) is found in all the provinces and in Nunavut. Commonly found along the shores of rivers and large creeks, this damselfly has a beautiful, butterfly-like flight.
Female River Jewelwings lay their eggs in the stems of submerged aquatic vegetation, 30 cm or more below the surface of the water; females can remain submerged for half an hour or more, while laying their eggs! Once hatched, the larvae spend at least two years in the water, before metamorphosing into adults. Adult River Jewelwings are distinguished by their spectacular metallic green bodies and their broad wings, which appear as if the outer half has been dipped in black ink. Adult females spend much of their time foraging in upland habitat and only return to the water to mate and lay eggs. Males however, spend most of their time defending their territories along the banks of rivers and large creeks. Once a female enters a male's territory, the male initiates an elaborate courtship dance. First, the male conducts a display flight over a potential egg-laying site in his territory. The flight displays the handsome markings on the hindwings and this may assure the female that he is of the correct species and a suitable mate. Next the male hovers in front of the female, until she allows him to mate. Finally, the female lays her eggs and the life cycle begins again.
The combination of being easy to observe and manipulate, together with a wide distribution and complex behaviour patterns, make these damselflies an excellent study species for a range of behavioural and ecological questions. River Jewelwings have taught scientists much about damselfly movement through upland habitat, courtship behaviour, and species discrimination during courtship. For both amateurs and professionals, these beautiful damselflies are endlessly fascinating to observe.
Results of general status assessment
Wild Species 2005 marks the first national assessment for odonates. The rankings for odonates were finished in November 2003 and reflect data available up to that time.
The majority of Canada's 209 odonates have Canada ranks of Secure (145 species, 69%, Figures 2- 4-i and 2-4-ii and Table 2-4-i). Twenty-seven species have Canada ranks of Sensitive (13%), and 28 species have Canada ranks of May Be At Risk (13%). No species have Canada ranks of At Risk because COSEWIC has not completed any status assessments for odonates. However, COSEWIC status assessments are currently in progress for two odonate species, Rapids Clubtail (Gomphus quadricolor) and Pygmy Clubtail, and a further nine species are currently on the candidate list for assessment by COSEWIC.
|May be at risk||28||7||4||0||9||0||0||33||43||10||16||10||25||0|
Threats to Canadian odonates
In order to successfully complete their life cycle, odonates require both aquatic and terrestrial habitats, and are therefore potentially vulnerable to habitat degradation and destruction both on land and in the water. In aquatic systems, destruction and degradation of wetlands, damming and channelling of rivers and streams, and water pollution can all negatively impact odonate populations. Recreational use of waterways can reduce the abundance and diversity of odonates, since boat wakes can kill individuals during the vulnerable emergence period. Odonates are also vulnerable to ecosystem changes resulting from invasion of exotic species. Modifications to land adjacent to aquatic habitat can affect odonates directly, by degrading the upland habitat they use to mature and hunt, and indirectly by affecting water quality.
This general status assessment shows that although more than two-thirds of Canada's odonates have a Canada rank of Secure, 13% are ranked May Be At Risk. Odonates and insects generally have not received as much attention from biologists and conservationists as well-studied groups, like birds and mammals. However, this general status assessment, which was made possible by the cooperative contributions of both amateur and professional field biologists, has aided COSEWIC in selecting a number of priority species for detailed status assessments. Detailed COSEWIC assessments will consolidate our knowledge of species ranked May Be At Risk, while amateur and professional field biologists across the country will continue to improve our knowledge of the life history and distribution of odonates in Canada. The vast areas of Canada where no one has ever looked for odonates makes the discovery of a new species a thrilling possibility!
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