Four-spotted Chaser

Libellula quadrimaculata (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: 40-48 mm

Abdomen length: 27-32 mm

Hindwing length: 32-40 mm

Larval body length: 18-28 mm

Other common names: Four-spotted skimmer

DESCRIPTION

Adult:  A large, robust dragonfly, with brown eyes and thorax, and a flattened abdomen that tapers to a distinct point, but is never wider than the thorax. The abdomen is brown, with the four final abdominal segments becoming black. Paler reticulated markings are visible on the upper surface of the abdomen and on the thorax (in fact these features are beneath the brown colour, which is translucent).There is a narrow yellow panel at the side of most abdominal segments. The sexes appear similar, and can most reliably be distinguished on the basis of the projections at the base of the abdomen, which form a 'V' shape in males but are straight in females.

 

Most distinctively, a black marking is present at the midpoint of each wing, along the leading edge (absent in immature individuals). Together with the black pterostigma, this gives the wing the characteristic four-spotted appearance. The base of each wing is amber, and in the forewing this is the only colouration present. There is a dark triangular marking at the base of each hindwing, which is crossed by pale wing veins. The extent of wing patterning in this species is variable (see Taxonomy).

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; short lateral spines are present on both segments. The larva has small eyes that face upwards when viewed from the front, with the tips lying below the top of the head. The labial palps have very shallow teeth. The abdomen is unpatterned. The larva is covered in numerous setae which trap accumulated debis, an adaptation for camouflage.

Similar species: The wing patterning in the four-spotted chaser is unique. Other chasers lack markings at the midpoint of the wing; additionally, these species have dark (not amber) markings at the base of the forewing. In the broad-bodied chaser (Libellula depressa), the abdomen is wider than the thorax at its widest point, the yellow abdominal panels are larger and oval in shape, and the hindwing has dark (not pale) venation at its base. The scarce chaser (Libellula fulva) has pale wing venation and little colouration at the base of the forewing, but lacks a 'spot', has no yellow markings at the sides of the abdomen, and the abdomen has a dark mid-dorsal line. The Eurasian baskettail (Epitheca bimaculata) exhibits superficially similar patterning, but has a more slender abdomen and lacks a wing spot. This species also differs behaviourally, being less inclined to perch and patrolling further offshore.

The similar broad-bodied chaser has larvae in which the eyes protrude above the top of the head (not always apparent in exuviae), deeply serrated teeth on the labial palps, and bands marking the abdomen (although these too may not always be apparent). The scarce chaser (L. fulva) has a prominent dorsal spine on the ninth abdominal segment. Other species with a similar body form have longer legs (the tibial-tarsal joint extends past the tip of the abdomen). The downy emerald (Cordulia aenea) is further distinguished by the deeply serrated labial teeth in this species. The black-tailed skimmer (Orthetrum cancellatum) lacks a dorsal spine on the eighth abdominal segment.

 

HABITAT

Standing water, typically with extensive vegetation. Although cosmopolitan, the species can be particularly abundant around acidic lakes and pools, often in heathland. Occasionally populations may occur in slow-flowing water, and sometimes in brackish pools. Four-spotted chasers can rapidly colonise newl-created pools.

 Larvae live among plant debris in the bottom substrate as they develop.

 

BEHAVIOUR

Males are highly territorial and will defend large areas, often entire pools, from competitors by flying sorties from a prominent perch within or near the waterbody. At high densities, individual territories become smaller and territoriality may be lost altogether when very large numbers of individuals are present. Animals fly with a rapid, jerky motion and will frequently pause to hover.

Four-spotted chasers are migratory, and will commonly be encountered far from suitable breeding sites.

Larvae are ambush predators, hiding among vegetation or burrowing into the sediment to capture unwary prey. When threatened by predators, they may feign death to avoid being eaten.

Breeding behaviour: Males launch sorties from their chosen perch to intercept females, and mating lasts only a few seconds. A single female may be targeted by multiple resident males in succession. Males guard females during oviposition, but animals do not lay eggs in tandem. The female oviposits in flight, releasing eggs within a gelatinous mass by flicking her abdomen into the water repeatedly.

Emergence: Mid-April to early September, with a peak in the UK in late May. Larvae emerge during daylight, onto marginal vegetation at the water's edge. Studies in Germany found that four-spotted chaser larvae emerged as much as a month earlier in the 1990s than in the 1980s as a response to climate warming.

Flight season: Late April to mid-September. Most animals are on the wing in summer.

 

BIOLOGY

Life cycle: Following oviposition, eggs take around four weeks to hatch. The species is typically semivoltine, requiring two years to complete development, but the larval stage may persist for longer.

 

ECOLOGY

The four-spotted chaser is known to be host to parasitic trematode worms; it has been suggested (Corbet & Brooks, 2008) that its high dispersal capabilities and migratory behaviour may make this species an important vector for spreading the parasite. In turn, the parasite is capable of infecting birds, and in areas where dragonflies form part of the diet, potentially also humans if the insect hosts are eaten raw.

 

TAXONOMY

Particularly extensively-marked forms of L. quadrimaculata, characterised by diffuse black markings near the wing tips as well as larger spots at the node (midpoint of the wing's leading edge), belong to the form L. q. praenubila, and can be quite common.

 

STATUS

The four-spotted chaser is very widespread and can be highly abundant; historically mass migrations of this species have been recorded. In the UK, this species is less abundant in the north-east of Britain, but records throughout the UK suggest that it may be expanding its range.

 

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

Smallshire, D. and Swash, A. 2010 Britain's Dragonflies: A field guide to the damselflies and dragonflies of Britain and Ireland 2nd Edition WILDGuides: 208 pp

Libellula quadrimaculata female. Buckinghamshire, UK.

Female four-spotted chaser. Buckinghamshire, United Kingdom

RANGE

A very widespread species, occurring across the temperate Northern Hemisphere (though absent from some far northern regions), south to Morocco. In the south of its Eurasian range populations are scattered, with the species being absent from much of the southern Iberian Peninsula, and scattered or uncommon in Turkey and the Balkans.

Range        Description        Habitat        Behaviour        Biology        Ecology        Taxonomy        Status        References