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History Dragonflies of the Family Aeshnidae in British Columbia: Biological Notes and Field Key, Based on Specimens in the Royal British Columbia Museum Collection Jens Proche and Simone Runyan 20 December 1996
Contents Abstract Species Profiles:
Conclusion
Abstract
Introduction
While none of the dragonflies in the family Aeshnidae are officially endangered or threatened in British Columbia (Harding et al., 1994), their wetland habitats have been heavily impacted over the last 100 years. For example, flood control measures and development have reduced the marshland between Penticton and Osoyoos to about 10-15% of what it once was (Cannings et al., 1987). As a result, the abundance and diversity of dragonflies which impressed collectors in the 1930s no longer exists (Whitehouse, 1941; Cannings, R.A., pers. comm. 1996). In this report, we have provided useful information for the professional biologist and the beginner naturalist. The introduction to dragonflies covers basic biology and fossil history. This is followed by a key to the Aeshnidae, which contains some of the largest and most conspicuous dragonflies in British Columbia. The key is designed to identify live specimens in the field without the aid of a microscope. Each of the 14 species within the family are profiled as to size, colours, habitat, flight period and range. Colour photos of specimens within the Royal British Columbia Museum (RBCM) collection accompany the species profiles. Areas of the province where more collection is needed are also identified.
Methods
and Materials Funds from Forest Renewal British Columbia (FRBC) have enabled the RBCM to hire co-operative education students to update and computerize data in the RBCM's natural history collections. As co-op students, we have entered data such as collection site, collector and date collected from specimen labels into a database. The information from each specimen is contained within one record in the Collections Information Entry and Reporting Application (CIERA), a FoxPro database designed by Orca Consulting Group Incorporated. Each specimen is given an extra label bearing a catalogue number. A search for this catalogue number in the database locates the record, which can then be updated at any time. To create the distribution maps for each species in the report, we found Universal Transverse Mercator (UTM) coordinates for all the collection sites associated with each specimen. We worked with a 1:50,000 map series which allowed accuracy within 100 metres for most sites. The UTM coordinates were then downloaded into the Quickmap mapping program and converted to dots on a map of British Columbia. (Not included in this version.) The field key to the Aeshnidae and introduction to the key was originally published in the summer 1996 issue of Cordillera magazine, Cannings (1996). Information for the species profiles was mostly taken from Cannings and Stuart (1977) by the RBCM.
Introduction to the Dragonflies
300 million years ago, in the moist, steamy swamps of the Carboniferous period, huge dragonflies with 70 cm wingspans swooped among tree-sized plants that looked like modern day Horsetails (Equisetum sp.) (Appleton, 1974; Scagel et al., 1969). Since that time, the dinosaurs have come and gone, flowering plants have evolved, and mammals have risen to be the dominant large organisms on the earth. Dragonflies have become much smaller; the largest in British Columbia today have wingspans of 10.5 cm. But as a credit to superb design, dragonfly morphology has changed very little. In all the insects, only the dragonfly and cockroach body plans can be recognized in fossils from the Carboniferous period through to the present (Appleton, 1974). A variety of characteristics separate dragonflies from the rest of the insect world and make them perfectly designed aerial predators. The large wings are one of the most distinguishing features. The wings of most insects are wedged between the dorsal and lateral plates of the thorax. Muscles attached to walls of the thorax contract and lever the wings up and down. In dragonflies, the muscles attach directly to the wings, allowing each of the four wings to move independently (Cannings and Stuart, 1977). Direct muscular control of each wing makes the dragonfly one of the most skilled and versatile insect aerialists. They can fly at speeds of up to 54 km/h when needed (Whitehouse, 1941), and can stop in an instant. Dragonflies can hover, and even fly backwards and sideways. The wings beat at a rate of approximately 20-90 beats per second, depending on speed and direction of flight (Appleton, 1974). This slow beat rate reduces the buzzing noise created by many insects in flight, and gives the dragonfly an excellent hunting advantage. The importance of flight to the dragonfly is emphasized by the fact that no other insect devotes such a large portion of its body weight to flight. In the genus Aeshna, wing muscles account for 24% of the body weight, compared to 13% for the honey bee (Appleton, 1974). The head is a remarkable piece of engineering wizardry. It is suspended on the pointed tip of the thorax and rests in an upright position under the influence of gravity, thus acting as a gyroscope to tell the dragonfly which way is up. The position of the head relative to the rest of the body is detected by sensory hairs. If the body strays from its horizontal position, wing movements act to bring the body back into alignment (Appleton, 1974). The dragonfly's large compound eyes take up two-thirds of its head. Each eye consists of about 30,000 tiny facets that enable easy detection of predators and prey (Appleton, 1974). Adult dragonflies are equipped with biting mouthparts well suited to crushing the exoskeletons of their insect prey (Cannings and Stuart, 1977). The thorax of the dragonfly is a strong box formed by the fusion of the second and third thoracic segments. This box is skewed so that the wings are pushed back, while the six legs are pushed forward toward the mouth (Appleton, 1974). This puts the wings at the dragonfly's centre of gravity on an angle so that the hindwing is just outside the zone of turbulence created by the forewing (Appleton, 1974). The spiny legs of the dragonfly form a basket in which it cradles its catch. Because the legs are directly under the mouth, the dragonfly can pass the prey to its mouth with ease and eat while still on the wing (Cannings and Stuart, 1977). Most people have seen dragonflies paired, flying in tandem around ponds in the summer. This method of mating is unique in the insect world (Cannings and Stewart, 1977). The males have accessory genitalia on the underside of the abdomen base. Sperm is transferred to these storage sites from the genital pore at the end of the abdomen. The male later finds a female and grasps her at the back of the head or prothorax, using appendages on the end of his abdomen. The female then curls her hind end up to the male's accessory genitalia to collect the sperm resulting in the wheel position (Cannings and Stewart, 1977). Several methods of oviposition are employed. The female may drag her abdomen over the surface of the pond, releasing eggs like a bomber. Or, if she has an ovipositor, a knifelike egg-laying organ, she may insert them into rotting wood or reeds at the pond's edge . Some males retain their hold on the female while she lays, in order to discourage other males from trying to mate with her. In other species, the males may hover above the female to guard her and chase away would-be suitors (Cannings and Stuart, 1977). Dragonflies of the genus Aeshna do not guard their females, so most females are secretive. Female Aeshna tuberculifera , or Black-tipped Darners, are coloured like males and further disguise themselves by flying like males, presumably to avoid harassment (Cannings, 1996). Eggs may hatch within a few weeks, or may overwinter, depending on the species. The maturation period of the larva is also variable, depending on the climate as well as the species. Larvae may mature and lay eggs of their own in a single summer in some warmer areas where the ponds are in danger of evaporating. Or they may take up to five years to reach adulthood in cold water where food is hard to obtain. The larva pass through 10 to 15 instars, or larval stages before reaching adulthood, shedding their skin and growing each time (Cannings and Stuart, 1977). Larvae are well adapted to life in ponds, lakes and streams. Water weeds oxygenate the water and provide food and shelter for organisms such as aquatic insects, tadpoles, minnows and crustaceans, which the larvae eat. The larvae are camouflaged in shades of green and brown . They may sit and wait for their prey to pass by, or they may actively stalk it (Cannings and Stuart, 1977). The extendible lower lip, or labium, of the larva normally rests folded beneath the larva's chin, but when the prey is close enough, the labium shoots out at lightening speed. Hooks on the end of the lip grasp the victim and drawn it back to the mouth to be eaten (Cannings and Stuart, 1977). Dragonfly larvae have a remarkable jet propulsion system for escaping from predators. They breathe by taking water through the anus into a gill-lined cavity. When frightened, the larva contracts the cavity, shooting water out behind and propelling the larva forward (Cannings and Stuart, 1977). Damselfly larva are much more slender and do not have internal gills. Biologists believe that damselfly larvae absorb oxygen through their cuticle or skin. The three fins at the end of the damselfly larva's abdomen may provide increased surface area for absorption, as well as assisting the larva in swimming (Ring pers. comm., 1995). Unlike butterflies, beetles and flies -- which enter a pupa stage before reaching adulthood -- dragonflies have no resting stage and are said to be hemimetabolous. The adult form develops inside the exoskeleton of the last larval instar. When the adult is ready to emerge, the larva climbs onto a plant or stone near the water's edge. The larval cuticle splits at the thorax and the new adult dragonfly slowly extracts itself from the exuviae . Hemolymph (insect blood) is pumped into the wing veins to expand the wings. The insect then hangs and rests while the wings dry. The exoskeleton of the newly hatched dragonfly, or teneral, is soft and its colours are cloudy for about a day (Cannings and Stuart, 1977). Colours may also change over the course of the adult's life. Adults often leave the pond for a week or two after hatching to take advantage of insect populations further afield (Cannings and Stuart, 1977). When they are sexually mature, they return to wetland areas to mate and breed. Males are more frequently observed at the water because they must select and defend a territory that will attract females (Cannings and Stuart, 1977). Spectacular aerial races and battles between males can be observed at the more crowded ponds. Although flight period varies among species, in British Columbia the greatest diversity and peak abundance of Aeshna occurs during July and August (Cannings, 1996). Even if they escape predators and survive to old age, adult dragonflies do not usually live much longer than 10 weeks (Cannings and Stuart, 1977).
Introduction
to the Darners: Family Aeshnidae The name Aeshna was coined by the famous Danish entomologist Fabricius in the 18th century (Cannings, 1996). The name may have resulted from a printer's error in spelling the Greek Aechma, "a spear" (Cannings and Stuart, 1977). Members of the genus Aeshna are called blue darners. They are generally dark brown with two parallel stripes on the thorax and regular patterns of spots on the abdomen in colours of blue, green and yellow. Males nearly always have blue spots on the abdomen, but the colouration of females is much more variable (Cannings, 1996). The term homeochromatic is used to describe females that have the same coloration as males, and heterochromatic to describe colour variants . The genus Aeshna consists of 75 species distributed worldwide, but it is especially dominant in the world's northern forests (Cannings, 1996). The wings of all aeshnids are transparent, with no spots or dark patches, though they may be tinted yellow or brown (Cannings and Stuart, 1977). The anal appendages of the male are long and often somewhat flattened. The females' ovipositors are designed for laying eggs in plant tissue (Cannings and Stuart, 1977). While some dragonfly larva simply sprawl on the bottom of the pond and wait for their prey, aeshnid larvae -- with their streamlined shape and keen eyesight -- often climb in aquatic vegetation, actively stalking their prey (Cannings and Stuart, 1977). The larvae are such rapacious predators that they will attack and eat any moving creature smaller than themselves, even their own kind (Cannings and Stuart, 1977). Most aeshnid larvae take from two to four years to develop (Cannings and Stuart, 1977). Aeshnids are strong fliers and they travel widely as young adults, sometimes appearing in towns and cities (Cannings and Stuart, 1977). Unfortunately for the dragonflies, their instincts do not always serve them correctly in the city. They apparently associate shiny surfaces with water: female aeshnids have been reported desperately trying to lay their eggs by dragging their abdomens along glossy man-made surfaces such as car roofs (Appleton, 1974).
Diagrammatic
Key Using this diagrammatic field key you can identify live adults of all species of Aeshna found in British Columbia. In fact, all species of the family Aeshnidae known in North America north of California and west of Manitoba are included. Colour and colour patterns, which are difficult to use in dried specimens, are stressed. Colour is much more variable in females than in males, and thus is less useful. Some small structural details are used, especially to separate females; a 10X hand lens and a millimetre ruler are critical equipment, as is a net. At first, the species will have to be learned in the hand, because many of the distinguishing features can be seen only at close range. Once the species are learned, many will be recognizable in the field, even at a distance. Captured dragonflies can easily be handled by reaching into the net and gently holding their wings together at the base between your thumb and forefinger. After examination they can be released unharmed. At each step of the key you have a choice to make between two sets of distinguishing characteristics. Read each alternative set before making your decision. The natural variation found among individuals of any species may sometimes make the decision difficult, but the characters have been selected to make the choices as clear as possible. Each choice will lead, via the arrows, either to a species name or to another set of characters from which to choose.
Length: Colours: Flight Period: A. californica is well known for its early springtime flight. In British Columbia the species may appear by late April and disappear by early August. Habitat: Alkaline ponds of the Chilcotin and Okanagan to forest lakes on Vancouver Island. Range: British Columbia south to Idaho, Arizona, and Baja California. In the British Columbia interior, the most northerly record is at Riske Creek in the Chilcotin, but on the coast, specimens have been found as far north as Rennel Sound on Graham Island .
Length: Colours: Flight Period: Recorded flight period in British Columbia is from 19 June to 9 October. Habitat: Ponds or lakes with a flooded margin. Bogs and fens with floating vegetation or logs. Ponds created by beaver dams offer a suitable habitat. In British Columbia A. canadensis is most common in the wet climate of Vancouver Island and the Fraser Valley. Range: British Columbia east to Quebec and Newfoundland, south to Maryland, Missouri and Washington. In British Columbia A. canadensis is recorded from Vancouver Island, east to Invermere . It has been found as far north as the Prince George area, but, surprisingly, one specimen was captured near Ross River in the Yukon in 1960 (Cannings et al., 1991).
Length: Colours: Flight Period: Late July to early October. Habitat: Slow streams and ponds in open marshes. Waters dominated by cattails and bulrush. Range: From British Columbia east through Saskatchewan to Nova Scotia; south to Maryland, Illinois, Colorado, and California. In British Columbia, A. constricta is recorded from Nicola, Enderby, Armstrong, Okanagan Landing, Penticton, Oliver and Creston . This species is not well known in British Columbia and is considered to have a southern transcontinental distribution.
Length: Colours: Flight Period: Recorded flight period is from 19 June to 14 October. Habitat: This is the largest of the Aeshna and is adapted to a variety of habitats. The species can be found in almost all forest regions of Canada. The Lake Darner is dominant in sparsely vegetated lakes, but may also be found at deep fens and sedge-bordered ponds. Range: Alaska east through the Northwest Territories to Labrador and Newfoundland; south to Massachusetts, Ohio, Wisconsin, Manitoba and Utah. A. eremita is found throughout British Columbia.
Length: Colours: Flight Period: Recorded flight period is from 27 May to 22 October. Most do not emerge until July. Habitat: A. interrupta is dominant in the prairie provinces. It is also common in rangeland ponds of drier plateaus and valleys of southern British Columbia. Adults may be found at sedgy ponds or lakes and around bog or fen pools. Range: Alaska east through the Northwest Territories to Newfoundland; south to New Hampshire, Michigan, North Dakota, and in the western mountains to New Mexico and California. Distribution in British Columbia extends throughout the province, but the species appears most common south of 55 degrees North . This may be due in part to inadequate collecting in the north because A. interrupta is quite common in the southern Yukon Territory. Three subspecies are thought to occur. A. i. interrupta inhabits the forests of Canada east of the Great Plains. A. i. lineata is found on the prairies and in the British Columbia interior. A. i. interna inhabits the mountains, typically ranging from the Selkirk Range and southern Rocky Mountains south to New Mexico. On the coast a form identical to the eastern A. interrupta appears. Since the ranges of these forms overlap considerably, their validity as subspecies is questionable.
Length: Colours: Flight Period: Recorded flight period is from 26 June to 2 September. Habitat: A. juncea is the most common of the Boreal species. This species often inhabits sedge potholes and marshes of forested regions in the mountains and northlands. Meandering streams and mossy fens also offer good habitat as long as sedges are present. Range: Alaska east through the Mackenzie Delta to Labrador; south to Newfoundland and New Hampshire, Ontario, Manitoba, and in the mountains from Alberta and British Columbia to Colorado. Also found in northern and alpine Europe and Asia. A. juncea is distributed throughout in British Columbia .
Length: Colours: Flight Period: Records for British Columbia are from 18 May to 16 October. Habitat: Common in warm standing waters with aquatic vegetation. Also found over open spaces such as fields, during sunny days. Range: British Columbia south through Idaho, Kansas, Colorado, and California to Texas, Arizona, Mexico and Panama. Distribution in British Columbia is widespread south of 51 degrees North . McBride marks the northern boundary to A. multicolor's range.
Aeshna palmata Hagan, Paddle-tailed Darner Length: Colours: Flight Period: Recorded flight period for British Columbia is from 22 May to 1 November. Habitat: A. palmata is the most common and most widely distributed Aeshna in British Columbia. The species has adapted to a range of larval habitats, from shaded ponds to warm springs. In northern regions it is restricted to low elevation lakes and ponds and is rare in muskeg habitats. Range: Alaska south through British Columbia and the Rocky Mountains of Alberta to California, Utah and Colorado; also in Cypress Hills Saskatchewan; Kamchatka. Distribution in British Columbia is widespread throughout the province.
Length: Colours: Flight Period: Recorded flight period is from 10 June to 28 August. Habitat: Ponds with aquatic moss are favored breeding sites, though in the Yukon, adult males patrol a range of waters, from bog pools to marl-bottomed lakes. Range: Yukon Territory east to the MacKenzie Delta, Hudson Bay, Ungava and Labrador; south to Newfoundland, New Hampshire, James Bay, Great Slave Lake, and south in the Rocky Mountains to 51 degrees North. The species have been recorded as far north as Herschel Island in the Beaufort Sea. In British Columbia A. septentrionalis has been found at Atlin, Haines Road near the Yukon border and Tweedsmuir Park .
Aeshna sitchensis Hagan, Zigzag Darner Length: Colours: Flight Period: Recorded flight period is from 10 June to 18 September. Habitat: Commonly found in shallow, northern fens and bogs which are evenly vegetated with sedges and moss. Range: Alaska east to Hudson Bay, Labrador, and Newfoundland; south to Maine, central Ontario, Michigan, southern Manitoba, the Alberta Rocky Mountains and British Columbia. Distribution in British Columbia ranges from Atlin to Field; coastal from Dundas Island and the Queen Charlotte Islands south to central Vancouver Island .
Length: Colours: Flight Period: Recorded flight period ranges from 20 July to 29 September. Habitat: Sphagnum bogs and cold northern swamps with aquatic mosses. Eggs are laid directly into floating moss. Range: The Yukon Territory north to the MacKenzie Delta; east to James Bay and Newfoundland; south to Nova Scotia, Quebec, central Ontario, northern Michigan and Manitoba. Also northern and central Europe. Distribution in British Columbia ranges from as far north as Keane Lake near the Yukon-British Columbia boarder. Most of the rare specimens have been collected from the central part of the province; Burns Lake and Crooked River southeast to Field. Also recorded at Courtenay, Vancouver Island . Notes: Closely related to A. juncea and often found in the same habitat.
Aeshna tuberculifera Walker, Black-tipped Darner Length: Colours: Flight Period: Recorded flight period in the Cordillera ranges from 16 July to 3 September. Habitat: Peat margined ponds and lakes. Eggs are laid above the water in emergent vegetation. Range: Coastal British Columbia and Washington. Wisconsin to Nova Scotia south to Pennsylvania and Indiana. In British Columbia the species is recorded in Nanaimo and Campbell River districts and east to Wells Gray Park and Golden .
Length: Colours: Flight Period: Recorded flight period is from early July to the end of the first week of November. Habitat: The Shadow Darner is fond of shade as well as sunshine, and is common in slow moving streams and still waters. The species is typical of forest lakes and Beaver ponds, as well as bogs and fens. Females oviposit in wet decaying wood. Range: The Yukon east to Hudson bay, Labrador, and Newfoundland; south to Alabama, Oklahoma, Utah and California. Distribution in British Columbia ranges from the northern portion of the province near the Yukon; southern Vancouver Island to the Rockies .
Length: Colours: Flight Period: Anax junius has an unusual life history. Mature adults arrive in the spring and early summer from the United States and the females begin to oviposit immediately. These adults usually disappear by the end of July. By August a new emergence of adults begins. Larval development takes about one year and these Canadian-born adults are thought to be the progeny of the previous year's spring migrants from the south. The late-emerging adults then migrate south to breed. In British Columbia, adults have been recorded from 29 April to 6 September. Habitat: The female oviposits in floating aquatic vegetation or in submerged decaying wood in still waters. Range: Alaska east to Nova Scotia and south to Panama; also the West Indies, Hawaii, and Tahiti. In Asia south from Kamchatka to Japan and China. In British Columbia, Anax junius is found mainly on southern Vancouver Island, in the Fraser Valley and the Okanagan Shuswap region. Northern records also indicate Canim Lake and Summit Lake, near Prince George
The dragonfly collection at the Royal British Columbia Museum contains more than 1,200 specimens of the family Aeshnidae from British Columbia. A great deal of the collecting within British Columbia has been done by Robert A. Cannings, Sydney G. Cannings, Gordon E. Hutchings and Crispin S. Guppy from the early 1970s to the present. Frank C. Whitehouse and George A. Hardy collected during the 1930s and 1940s. Other specimens of aeshnids from British Columbia are housed in the Spencer Entomological Museum at the University of British Columbia and the Canadian National Collection, Agriculture Canada, Ottawa, but these were not mapped in this report. Collecting is required in the northern and northeastern regions of the province. Nine of the fourteen species of Aeshnidae that occur in British Columbia are also known from the Yukon (Cannings et al., 1991). These are: A. canadensis, A. eremita, A. interrupta, A. juncea, A. palmata, A. septentrionalis, A. sitchensis, A. subarctica and A. umbrosa. Despite the fact that most of these species are quite common in the Yukon, the Royal British Columbia Museum has only a few specimens from northern British Columbia. In the case of A. sitchensis, the RBCM has no specimens from the northern half of the province. The University of British Columbia, however, has records from Atlin, near the British Columbia-Yukon border. Clearly, more collecting should be done in the less accessible and less populated northern and central regions of the province. The ecoregions of the taiga plains and boreal plains as well as the northern boreal mountains and sub-boreal interior are particularly under-represented. The RBCM has only 11 specimens of A. septentrionalis, the most boreal of the aeshnids, and 8 specimens of A. subarctica, another northern species. A. constricta and Anax junius are uncommon and restricted to the southern portion of British Columbia. The RBCM has fewer than 15 specimens of each. If any members of the family Aeshnidae are to become threatened by human development in British Columbia, it will be these. There are 14 specimens of A. tuberculifera in the RBCM collection. Though A. tuberculifera is also restricted to the southern half of the province, it is less vulnerable to human activity because it prefers peat-margined ponds and lakes in more remote locations. The RBCM has 316 specimens of A. palmata, suggesting that it is one of the most common aeshnids in British Columbia. However, no RBCM specimens come from the taiga and boreal plains. The collection has 250 specimens of A. eremita, but 117 of these are larvae from a single location on Salt Spring Island. If these larvae are not considered, there are about 130 specimens of both A. eremita and A. interrupta. A. eremita is common in forested mountain lakes. A. interrupta is common in grassland ponds, peatlands and wetlands over most of the province, but is notably absent from the Queen Charlotte Islands. Although the RBCM has only 86 specimens of A. juncea, it is as widely distributed across the province as A. eremita. It is important to observe that the distribution maps in this report only represent specimens in the RBCM collection. (Maps not included in this version.) This database should be merged with that of the University of British Columbia collection so that a more complete understanding of the species distributions can be developed. In some cases, our knowledge of an entire region, especially in the north, is the result of a single visit to a particular locality. Therefore, illustrated distributions should be regarded with some caution until more collections are made in the north. Further collecting there may also extend the northern limits of the ranges of those species largely restricted to the south. Unless specimens are collected properly, along with certain information such as habitat, location, date and collector, the specimen may be of little scientific value. Collectors of Odonata recommend the use of acetone as a drying agent because it helps preserve the bright colours of the body. Other information on collecting techniques may be found in The Dragonflies of British Columbia (Cannings and Stuart, 1977, Royal BC Museum publication) and The Insects and Arachnids of Canada, Part 1 (Martin, 1978).
This report is based heavily on the work of Robert A. Cannings. We are very much in his debt for allowing us to use his material, and for reviewing the report. Without the financial support of the Forest Renewal British Columbia fund, the RBCM would have been unable to hire us to help curate the insect collection. The Conservation Data Centre staff kindly allowed us to use their collection of maps of British Columbia. Tara Steigenberger produced the key, gave computer advice and produced the electronic version for the Web. Lesley Kennes, Phil Lambert and John Pinder-Moss provided much help with mapping. Andrew Niemann scanned the photos for the internet. We are grateful to all of them.
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