Broad-bodied Chaser

Libellula depressa (Linnaeus, 1758)

Family: Libellulidae - Darters, Skimmers and Chasers

Order: Odonata (Epiprocta) - Dragonflies

Class: Insecta

Phylum: Arthropoda

Kingdom: Animalia

Red List status: Not evaluated

Total length: 39-48 mm

Abdomen length: 22-31 mm

Hindwing length: 32-38 mm

Larval body length: 22.5-25 mm

DESCRIPTION

Adult:  A large, very robust dragonfly, with a flattened abdomen that is broader than the thorax at its widest point. The male abdomen is a pale dusty blue, actually a pruinose covering over a yellow ground colour; oval-shaped yellow 'panels' at the edges of the third to eighth abdominal segments in both sexes are characteristic of this species, although some or all may become obscured by the bluish colouring in adult males. Immature males lack pruinosity, and both the abdomen and thorax are orange-yellow. Females are dark greenish-brown, with a broader abdomen than the male; in flight they may resemble large hornets. In both sexes, a prominent central line running the length of the abdomen is present.

Female broad-bodied chaser

 

Each wing has a distinct brown marking at its base. This is of equal length in the fore- and hindwings, but is a broad triangle in the latter while the forewing pattern appears more bar-like. The adult thorax is brown, with broad, greenish-white antehumeral stripes that contrast strongly with the dark thorax. In the immature, the antehumeral stripes are less well-developed and are pale yellow.

Larva: The larva is squat and robust, with short legs; the joint between the final two sections of the hindleg (tibial-tarsal joint) does not extend past the tip of the abdomen when the leg is stretched out. A dorsal spine is present on the penultimate abdominal segment (segment 8), but not on segment 9. The larva has small eyes that face upwards when viewed from the front, with the tips extending above the top of the head. The labial palps have deeply serrated teeth. The abdomen is marked with dark longitudinal bands, but these may not always be apparent. A yellow mark may be present on each labial palp.

Broad-bodied chaser exuvium.
Male broad-bodied chaser. Note the dark wing markings, broad abdomen and pale antehumeral stripes.

Similar species: The combination of large, dark patterns at the wing bases, blue colouration in the male and robust body distinguish the broad-bodied chaser from most species. Skimmers (Orthetrum) are often pruinose blue, and may be robustly built, but never have dark patches on the wings. The Eurasian baskettail (Epitheca bimaculata) has dark patches on the hindwings, but never on the forewings, and broad-bodied chaser females never have extensive black patterning on the abdomen. The four-spotted chaser (Libellula quadrimaculata) likewise lacks brown markings at the base of the forewing. This species also exhibits a dark marking at the centre of the leading edge of each wing that is absent in the broad-bodied chaser. Wing markings are less extensive in the scarce chaser (L. fulva), which also lacks yellow markings on the abdomen and broad antehumeral stripes. These latter species typically prefer habitats with greater vegetation cover. Males of this species can be definitively identified by the presence of two spines on the underside of the abdomen base, a character unique among British dragonflies.

The presence of a dorsal spine on abdominal segment 8 distinguishes the larva from otherwise similar

skimmer species. These species also have longer legs (tibial-tarsal joint extends past the abdomen), as do emerald (Corduliidae) larvae. The scarce chaser has a prominent spine on the 9th abdominal segment, and less strongly serrated teeth. The four-spotted chaser has less strongly serrated teeth, no patterning on the abdomen, and the tips of the eyes lie below the top of the head.

 

HABITAT

Standing water, often early-successional habits with little vegetation and exposure to the sun. Small, shallow pools are particularly favoured, and the species will rapidly colonise newly-cleared areas. Larvae are bottom-dwelling, typically burrowing into fine detritus, stone, sand or mud, and may survive desiccation by taking refuge under debris if the pond dries out.

 

BEHAVIOUR

Males are highly territorial and will defend large areas, often entire pools, from competitors by flying sorties from a prominent perch nearby. Animals will defend territories for as long as there are mating opportunities. An animal that doesn't copulate with a female for a day or two will abandon his territory in favour of searching for another site.

Broad-bodied chasers may sometimes attack potential predators; perhaps taking advantage of their similar appearance in flight, females have been observed harrassing hornets (Corbet & Brooks, 2008). Conversely, males of this species may sometimes mistake hornets for female L. depressa and seize them in an attempt to mate (Corbet & Brooks, 2008)!

Diet: Dragonflies are opportunistic predators during all life stages. In addition, L. depressa larvae may engage in filial callibalism, with more rapidly-developing larvae in brood preying on smaller siblings (Corbet & Brooks, 2008). Larvae forage predominantly by touch.

Breeding behaviour: Once a male has located a potential mating site, he will patrol it and settle on a number of different perches while seeking out females. Only following a successful mating will he claim the copulation site as his territory. Males guard females during oviposition, but animals do not lay eggs in tandem. Females lay eggs in clusters on the surface of algae or floating plants. A female will typically test the quality of the available substrate by brushing the surface of the water several times with her abdomen before starting to deposit eggs. Males may mate multiple times in a day, and appear to become more sexually active the earlier in the day he secures his first mating.

Emergence: From mid-April to late July in the UK. Increasing numbers of animals emerge throughout May, reaching a peak at the end of the month. Larvae emerge onto low vegetation at the pond margins, and emergence may be strongly synchronised.

Flight season: Late April to mid-September. Most animals are on the wing in May and June. In Germany, warmer temperatures have resulted in flight periods starting up to a month earlier than in the 1980s (Corbet & Brooks, 2008).

 

BIOLOGY

Life cycle: The species is typically semivoltine, requiring two years to complete development, but may take only a single year.

 

STATUS

The broad-bodied chaser is common throughout its range; however the loss of ponds due to agricultural intensification has led to this widespread species becoming more local in distribution in East Anglia in the 20th Century, a trend that is probably reflected in the rest of Britain (Corbet & Brooks, 2008).

 

REFERENCES

 

Cham, S. 2007 Field Guide to the larvae and exuviae of British Dragonflies Volume 1: Dragonflies (Anisoptera) The British Dragonfly Society: 76 pp.

Corbet, P. and Brooks, S. 2008 Dragonflies New Naturalist Series 106, Harper-Collins, London: 456pp

Dijkstra, K-D.B. and Lewington, R. 2006 Field Guide to the Dragonflies of Britain and Europe British Wildlife Publishing: 320 pp

Female Libellula depressa. Buckinghamshire, United Kingdom

Male broad-bodied chaser. Buckinghamshire, United Kingdom

RANGE

Almost Europe-wide, including major offshore islands, east to central Asia. Absent only from Ireland, northern Britain and northern Scandinavia in the north, and from the southerly tip of Spain in the south. In the UK, the species is expanding its range northwards.

Range        Description        Habitat        Behaviour        Biology        Status        References