Odonata - Rithet's Bog Conservation Society

Dragonflies and Damselflies

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INTRODUCTION

This species list presents the results from continuous observations of dragonflies and damselflies by society members since 2008, plus some historic observations recorded on the University of British Columbia’s E-Fauna BC website. Much of the additional information presented in this section is derived from the publications in our References list, although we also include personal communications from our time spent observing the wildlife at Rithet’s Bog.

Rithet’s Bog, with its wide variety of wetlands, has traditionally supported diverse and abundant populations of dragonflies and damselflies, especially damselflies. Unfortunately, a recent series of several exceptionally dry summers and resultant low water table in the wetlands has resulted in precipitous declines. Currently the numbers being observed are much lower than the historic abundances we discuss in this section. We will continue to monitor odonate populations to determine if this trend is a temporary anomaly or an ongoing trend of climate change.

SPECIES LIST

Common Name	Scientific Name	Button
DRAGONFLIES	Suborder ANISOPTERA
Skimmers	Family Libellulidae
Eight-Spotted Skimmer	Libellula forensis
Four-Spotted Skimmer	Libellula quadrimaculata
Common Whitetail	Plathemis lydia
Variegated Meadowhawk	Sympetrum corruptum
Cardinal Meadowhawk	Sympetrum illotum
Red-Veined Meadowhawk	Sympetrum madidum
Striped Meadowhawk	Sympetrum pallipes	open
Autumn Meadowhawk	Sympetrum vicinum
Black Saddlebags	Tramea lacerata
Darners	Family Aeshnidae
Paddle-Tailed Darner	Aeshna palmata
Shadow Darner	Aeshna umbrosa
California Darner	Rhionaeschna californica
Blue-Eyed Darner	Rhionaeschna multicolor
DAMSELFLIES	Suborder ZYGOPTERA
Pond Damsels	Family Coenagrionidae
Western Red Damsel	Amphiagrion abbreviatum
Pacific Forktail	Ischnura cervula	open
Swift Forktail	Ischnura erratica
Western Forktail	Ischnura perparva
Spreadwings	Family Lestidae
Spotted Spreadwing	Lestes congener
Northern Spreadwing	Lestes disjunctus
Emerald Spreadwing	Lestes dryas
Lyre-Tipped Spreadwing	Lestes unguiculatus

Biology

TAXONOMY

The dragonflies and damselflies are insects belonging to the order Odonata, a group of insects closely related to the Mayflies (order Ephemeroptera). There are three suborders within the Odonata, the Anisoptera, the Anisozygoptera and the Zygoptera. The Anisozygoptera are a relic suborder of mostly extinct species, with only three living species found in Asia, so they will not be discussed here.

The Odonata belong to one of the oldest groups of flying insects with a fossil lineage that goes back 325 million years. One fossil species, from 300 million years ago, is the largest known flying insect with a wingspan of 70 cm. This species lived during a period of higher atmospheric oxygen levels which may have allowed its respiratory system to support such a large and active insect.

Dragonflies (Suborder Anisoptera)

Dragonflies are medium to large (30 to 70 mm long), fairly robust and often quite noticeable. Their forewings and hindwings are different shapes and are held perpendicular to the body when perched. Their eyes are close together, either touching or with a small space between.

Two families occur at Rithet's Bog, the Skimmers (Libellulidae) and the Darners (Aeshnidae). Skimmers are medium sized dragonflies that usually perch horizontally on vegetation or the ground and often return to favourite perches. Darners are large dragonflies, often with blue markings. They are usually seen flying in open areas, sometimes at a considerable distance from water. They only perch occasionally by hanging vertically from vegetation.

Damselflies, (Suborder Zygoptera)

Damselflies are small (25 to 40 mm long), slender and often inconspicuous. Their fore and hind wings are the same shape and when perched their wings are folded backward over their abdomens. Their eyes are widely spaced, protruding from the side of the head.

Two families occur at Rithet's Bog, Pond Damsels (Coenagrionidae) and Spreadwings (Lestidae). Pond Damsels perch with their wings folded completely back over their abdomens. Spreadwings perch with their wings angled backwards at 45 degrees.

ANATOMY

This section points out some basic anatomical features useful for identifying species.

Head

The colour of the eyes and face.
Dragonflies may have a dark horizontal line across the face.
Dragonflies may have a coloured spot where the eyes and face converge, called the vertex.
Damselflies may have coloured postocular spots on the backs of their eyes, which may also be joined by a horizontal bar to create a dumbbell shape.

Thorax

The colour, shape and location of stripes or spots on the sides and/or top on the thorax
The shape and colour of the pterostigma on the wings.
The colour patterns of the membranes and veins on the wings.
Leg colour.

Abdomen

The colour, shape and location of markings on the top and sides of the abdomen.
For damselflies, the colour and markings on segments 8, 9 and 10 may be important.
The shape of the abdominal appendages, especially for males.

Figure 1. Dragonfly Anatomy.

Figure 2. Damselfly Anatomy.

LIFE CYCLE

Odonates are hemimetabolous, which means they undergo incomplete metamorphosis. They have a three-stage life cycle of egg, larva (nymph) and adult. There is no pupal stage and although the larva looks different than the adult, it has the same basic insect body plan of a head, a thorax with six legs and a segmented abdomen. Eggs are usually laid in or near water during summer through early fall. Depending on the species eggs may hatch into larvae quickly or they may remain dormant until hatching in late fall to early spring. Odonate larvae are aquatic, living in a wide variety of wetlands. Many species spend most of their life as larvae, from several months to a few years. This is the growth stage and larvae undergo up to fifteen molts of their exoskeletons to accommodate their increasing body size. Larvae are initially wingless, but developed wings folded within sheaths on their backs. Damselfly larvae have three feathery gills attached to the end of their abdomens. Odonate larvae are sometimes referred to as nymphs or naiads. Larvae that are fully grown emerge from the water, often climbing plant stems. The back of the exoskeleton then splits open and the adult wriggles out. The empty larval exoskeleton that is left behind is called an exuvium. Adults emerge at their full body size and do not undergo any further molts. The adult life span is short, ranging from a few weeks to a few months. Adults go through three sub-stages:

Tenerals are adults as they emerge from the larval exoskeleton, unfold their wings, and allow the new exoskeleton to dry. Tenerals often have subdued brown or yellowish colour patterns. This period is very vulnerable to predation and usually occurs under cover of darkness. Tenerals are easily damaged and should not be handled.
Immatures are adults in the process of developing full adult colour patterns and reaching sexual maturity. Immatures often wander away from water to feed and complete their development.
Mature adults, which have completed their development, return to the wetlands to breed and complete their life cycle.

Figure 3. Dragonfly larva.

Figure 4. Damselfly larva.

Figure 5. Dragonfly exuvium.

Figure 6. Dragonfly teneral
emerging and unfolding its wings.

ECOLOGY

Dragonflies and damselflies, in both their adult and larval stages, are mid level predators. Larvae prey on a wide variety of aquatic invertebrates and occasionally small fish. Adults prey on other flying insects. It turn, they provide prey for larger, higher level predators such as larger fish, amphibians and birds. As such, odonates are important indicators of biodiversity and ecological integrity in wetland ecosystems. Odonate populations reflect the state of the lower trophic levels of small predators and herbivores that they depend on. Odonate populations also support the higher trophic levels of larger predators. The International Union for Conservation of Nature (IUCN) has set up a Dragonfly Specialist Group to monitor odonate populations as indicators of the decline of wetland ecosystems.

Some species are voracious predators of mosquitoes. Adults prey on adult flying mosquitoes and larvae prey on the aquatic larvae of mosquitoes. This is an example of how healthy ecosystems with good levels of biodiversity provide us with ecological services such as natural and free pest control.

One of the benefits of having a complex, multistage life cycle with larvae and adults occupying different niches within the overall ecosystem, is that the larvae and adults do not compete for the same resources, especially food. This means the ecosystem can support larger populations than if both life stages were competing for the same resources.

Figure 7. Pacific Forktail female eating a mosquito.

References

Canning, Robert A. 2002. Introducing the Dragonflies of British Columbia and the Yukon. Royal British Columbia Museum, Victoria, BC, Canada. 96 pp.

An excellent field guide and introduction to the damselflies and dragonflies of British Columbia. Useful for both beginners and enthusiasts. It covers the species likely to be seen in our region and other parts of BC. Some species names have been revised since publication.

Unknown. 2010.
Checklist to the Dragonflies and Damselflies of
the Victoria Region. Metchosin Biodiversity
Project, Metchosin. 4 pp.

A single sheet checklist of the species likely to be seen in our area. Also, a diagram of anatomical features useful for identifying species.

Canning, Robert A. 2007.
Dragonflies and Damselflies of Spencer’s Pond, Langford. Royal British Columbia
Museum, Victoria, BC, Canada. 9 pp.

A short paper describing the odonate fauna of Spencer’s Pond in Langford. It covers several of the common species seen in our area. It also includes some interesting background information about dragonflies and damselflies. A good accessible introduction to the Odonata.

Klinkenberg, Brian (Editor). 2015. E-Fauna BC: Electronic Atlas of the Wildlife of British Columbia. Lab for Advanced Spatial Analysis, University of British Columbia,
Vancouver, BC, Canada.

This link goes directly to the Odonata photo gallery which includes distribution maps of the species reported in BC. The complete e-Fauna BC website covers all the fauna of BC. It includes additional information about wildlife
in BC.

Paulson, Dennis R. 2009.
Dragonflies and Damselflies of the West. Princeton Field Guides. Princeton University Press, Princeton and Oxford. 535 pp.

This is the definitive field guide for the damselflies and dragonflies of western North America. Species descriptions are more detailed and cover many species that do not occur in our region. For the serious enthusiast, especially if you are travelling outside of BC.

Paulson, Dennis R. 1999.
Dragonflies of Washington. Seattle Audubon
Society, Seattle. 32 pp.

An introductory field guide for Washington State, but many of the species are also seen in BC and on Vancouver Island. No longer in print.