Dragonflies of the Golfo Dulce Region, Costa Rica
Piedras Blancas National Park “Regenwald der Österreicher”
Printed with generous support from the Austrian Federal Ministry of Agriculture, Forestry, Environment and Water Management
1 Authors
Stefan Schneeweihs
Department of Population Ecology University of Vienna
Rennweg 14, 1030 Vienna, Austria
Roland Albert Werner Huber Anton Weissenhofer
Department of Chemical Ecology Department of Ultrastructure Department of Ultrastructure and Ecosystem Research Research and Palynology Research and Palynology University of Vienna University of Vienna University of Vienna
Rennweg 14, 1030, Vienna, Rennweg 14, 1030, Vienna, Rennweg 14, 1030, Vienna, Austria Austria Austria
[email protected] [email protected] [email protected]
2 Contents
The “Tropical Research Station La Gamba” ...... 4
The rainforests of the Golfo Dulce region ...... 6
Introduction ...... 8
History and diversity of dragonflies ...... 8
Adults and larvae ...... 8
Life cycle ...... 9
Morphology of the adult ...... 10
Identification ...... 11
Tropical dragonflies ...... 11
Odonatological field trips around La Gamba ...... 12
Forests ...... 12
Cultivated landscapes ...... 13
Forest margins ...... 13
Zygoptera ...... 14
Polythoridae ...... 14
Calopterygidae ...... 16
Megapodagrionidae ...... 18
Pseudostigmatidae ...... 20
Protoneuridae ...... 21
Coenagrionidae ...... 23
Anisoptera ...... 28
Gomphidae ...... 28
Libellulidae ...... 29
Diversity of dragonflies in La Gamba ...... 50
Acknowledgements ...... 50
References ...... 51
Dragonflies on the web ...... 51
Picture credits ...... 52
3 Introduction
Visitors to the La Gamba Research ecosystem. Today the order Odonata (drag - Station will find a rich array of tropical life. onflies) is divided into three suborders, the As well as an overwhelming diversity of most common being the smaller Zygoptera plants, they will see birds and butterflies, (also known as damselflies) and the larger two of the most popular and conspicuous Anisoptera. A third suborder, the groups of animals. Hummingbirds, noisy Anisozygoptera, which combines character - toucans, and brilliant butterflies like the iri - istics of the other two groups, is represented descent Morpho or the spectacular Heliconius by two species in Nepal and Japan. are well known throughout the world. But Approximately 5700 species have been there are many other groups which are just described so far, with almost equal numbers as recognisable yet not as widely known. in Zygoptera and Anisoptera. Because larval Unfortunately there is often a dearth of growth responds positively to temperature, knowledge about such organisms, and access dragonflies are assumed to have developed to the relevant literature is difficult. in a warm climate. Today the greatest diver - Sometimes, however, we just need a little sity is found in tropical regions, declining help to find them. Dragonflies are skilled towards higher latitudes. Areas of the high - fliers, fearless predators, and passionate est diversty are found in South America and lovers, and once you notice them, you will South East Asia, especially in montane find them fascinating. regions where examples of previously The ecology and behaviour of the Central unknown species are often reported. American dragonfly fauna has been laid out in detail in the specialist literature (see refer - Adults and larvae ences), and more interested readers are invit - Zygoptera and Anisoptera can be easily ed to consult these sources. This booklet is identified as adults and larvae. Adult designed as a pocket guide to the identifica - Zygoptera are usually finely built insects tion of the most frequently observed species with slender abdomens. The eyes are sepa - around La Gamba. The descriptions of char - rated and situated laterally on the head. acteristics and differences between the Their fore wings and hind wings are fairly species are limited to essential information. similar in shape and venation, and are held Although identification can be difficult, and over the abdomen when resting. In flight for some species beyond the scope of this they are less acrobatic than Anisoptera, and booklet, it should be possible to recognise are often found patrolling in dense vegeta - most of the common species present in the tion near the water’s edge. The larvae of region. For the interested observer, this Zygoptera are small and slender, this shape booklet will serve as an introduction to the often appearing pronounced by the presence diversity of a fascinating group of animals. of three flattened, elongated and highly tra - We hope it will raise awareness of the diver - cheate caudal appendages that serve as res - sity of dragonflies, but also of how urgently piratory organs. Three tropical families form we need to work for their conservation. the exception, showing either lateral gills on the abdomen (Euphaeidae and History and diversity of dragonflies Polythoridae), or gill tufts at the end of the The first fossil records of a group called abdomen (Amphipterygidae). Protodonata, closely resembling today’s Adult Anisoptera are built robustly, with dragonflies and thought to represent their a long or stout abdomen. Their large eyes ancestral form, date from the Upper cover almost the whole head and meet on Carboniferous period 325 million years ago. top of the head, or they can be slightly sepa - With a wingspan of 70 cm, Meganeura monyi rated as in the family Gomphidae. The wings was one of the largest insects ever to have differ in shape and venation and are held lived on the planet. Today’s dragonflies are open when resting. Anisoptera can be considerably smaller, but these ancient observed perching on exposed structures insects still have a valuable place in the along banks, or patrolling for hours over the
8 water surface. The larvae are stout and have ronmental factors like the reflection of the three strong spines instead of lamellate aquatic surface, and the vegetation structure. appendages. They breathe by ‘rectal ventila - After one or more weeks the embryo will tion’, pumping water through the rectum, have completely developed, and the first where a tracheate organ serves for gas larva (prolarva) will be ready to hatch from exchange. Water can be expelled from the the egg. Subsequently, having reached the rectum very forcefully, so that the larva water (in the case of endophytic eggs), the swims forward. This ‘jet propulsion’ is also prolarva starts to moult (i.e. to leave the old used to escape predators. cuticula), in a process called ‘ecdysis’. Larvae and adults are predators and fair - During the larval phase, which can last from ly opportunistic in their choice for prey, a few weeks up to several years, up to 15 although specialisation does occur (see ecdyses are completed, separated by periods Pseudostigmatidae). Both developmental of foraging behaviour and growth. In tem - stages are perfectly adapted to this lifestyle. perate regions, eggs or larvae can display a Larvae actively search out or ambush their diapause, a reduction of metabolism and prey, detecting it visually or by touch, and growth during winter. capture it by the rapid protraction of the The final larval stage, at which an adult modified lower lip (or ‘labium’) which forms is contained within the larval skin, sees the the so-called ‘mask’. Adults detect prey with larva leaving the water for emergence. This their large eyes. In flight, they can turn spectacular scene usually takes place shortly quickly, hover, and even fly backwards, before dawn. The larva climbs up a suitable since the flight muscles insert directly on the structure, often a piece of aquatic vegetation, wing base, allowing them to move each pair and searches for a firm grip with its legs. The of wings independently. Even fast-flying larval skin then bursts at pre-formed points, prey such as other dragonflies can be cap - and the young adult leaves the skin. After a tured by their acrobatic manoeuvres, held by short rest the adult unfolds its wings and their legs, and then manipulated with their abdomen by pumping in haemolymph. After sharp mandibles. emergence, the smooth and shimmering skin first has to harden. Then the dragonfly sets Life cycle off on its maiden flight, leaving the site of Dragonflies are hemimetabolic insects, emergence. exhibiting incomplete metamorphosis and Young adults spend their first days on lacking a pupal stage like that in butterflies; the side of the water in order to build up fat the adult develops during the last larval reserves, and to avoid interference from stage. Their life cycle comprises three phases: mature and territorial dragonflies. The sexu - egg, several larval stages, and adult. The lar - al organs are not yet fully developed, and vae live predominantly in fresh water, inhab - they start to mature during this period. In iting lakes, streams, bogs, and ephemeral some tropical species, when breeding habi - water bodies. Only a handful of species are tats have dried out, this pre-reproductive known to develop in the brackish water of time can be prolonged for months until the marine marshes, or to have terrestrial larvae. beginning of the next wet season. When the Many species are generalists, capable of sexual organs have fully developed, the inhabiting a wide spectrum of freshwater adults turn to suitable water bodies for systems. Some species, however, have nar - reproduction. row breeding site requirements and are thus Males spend many days at reproductive sensitive to disturbances and habitat destruc - sites, where they establish temporary territo - tion. Many of these specialists are rare, but ries that are defended against other males. they can be used for the assessment of eco - Females are often dispersed around other logical freshwater status. habitats and only visit the water bodies for After mating, the female lays fertilised copulation and oviposition. When a female eggs either on the water (exophytic), or into enters a territory, the male flies up and tries (sometimes submerged) plants (endophytic). to grasp her with the caudal appendages, on Before oviposition, suitable habitats for the female’s thorax in the case of Zygoptera, development are selected by the adults. and on her head in Anisoptera. The male During this selection they orientate on envi - then bends its abdomen forward to transfer
9 sperm from its sexual organs to its copula - Morphology of the adult tion organ. Finally, the female bends her The body of a dragonfly is separated into abdomen forward to bring her genitals into head, thorax and abdomen. The head bears contact with the copulation organ of the two large compound eyes, three median male, forming the ‘wheel of love’ (see ocelli, and two short antennae. Between the Libellula herculea ). With its copulation organ, eyes, the ‘frons’ forms the frontal part of the the male is able to remove sperm from previ - head. Below the frons, the labrum covers the ous copulations with other males and trans - mouthparts, which handle prey. The fer its own sperm into the female. Copulation colouration of eyes, frons, and labrum can be can take place while airborne or resting, and important characteristics for identification. may take anything from a few seconds to The thorax consists of three segments, each many minutes. The female can start to lay with a pair of legs. The first segment (protho - eggs immediately after copulation. Males rax) is short. The second and third segments often guard the female during oviposition, are fused and dorsally inclined backwards, either still attached or hovering next to her, and each has a pair of wings. The wings have to avoid other males attempting to copulate. five major veins and numerous crossveins. The front margin of the wing is formed by a vein called the ‘costa’. Details of venation are variable, but two conspicuous structures are present in all species. The ‘nodus’ is a strong crossvein, inserted at the front edge of the wing approximately half way along its length. The ‘pterostigma’ is a dark cell at the distal part of the wing on the costal side. The base of the wing can be narrow for the length of several cells (petiolate), extended, or nei - ther. The colouration and markings on the wings can be helpful characteristics for iden - tification. The abdomen consists of ten segments of Front view of the head of an Anisoptera ( Macrothemis sp. variable length. The first two segments are Libellulidae) short, segments 3–7 are long, and segments
Body regions of a male Zygoptera ( Acanthagrion inexpectum )
10 8–10 become shorter again. In males, seg - The most frequently observed forms of ments 2 and 3 bear the copulation organ ven - different species are illustrated in this book - trally. Females have ovipositors at the ven - let. If an observed individual does not fit any tral side of segment 8, sometimes extending of the photographs, this may be for one of to the tip of the abdomen, or a small vulvar two reasons. Either the species is not includ - lamina. At the end of the abdomen are the ed in the booklet, or the individual is of a dif - appendages, two upper and two lower in ferent sex or age. The following caveats have Zygoptera males, and two upper and one to be kept in mind during identification: lower in Anisoptera. species of the same genus may be similarly coloured; colouration may differ between Identification males and females of the same species; pre- Characteristics for unambiguous identifi - reproductive males often resemble females cation include wing venation and the struc - and usually become darker before entering ture of the male copulation organ or the the reproductive period; the shallow ovipositor. Examination of these structures colouration of recently emerged adults turns requires specialist knowledge and the ability into their characteristic pattern after several to capture individuals. Colouration, howev - hours, but wing markings may need longer er, can also be useful for identification, to become fully developed. Descriptions of although species–level determination is not immature and mature forms, and males and always possible. Any individuals observed females, are given in the text wherever they should be compared with the photographs, are available. Species closely resembling sizes, and descriptions of details in this book - each other are also mentioned in the text. let. The availability of aquatic habitats for Males can be recognised by the presence larval development constrains reproduction of a secondary copulation organ at the ven - in dragonflies, and consequently the rainy tral side of segments 2 and 3 of the abdomen, season marks the climax of the reproductive which forms a small but prominent structure period for many species. Adults of some absent in females. Females may have a con - species may be absent during the dry season, spicuous ovipositor on the ventral side at the either not yet emerged from their larval end of the abdomen. In Anisoptera, the stage, or occupying alternative habitats. It is ovipositor may be reduced to a small lami - therefore possible that not all species present nate structure arising from the end of seg - in the region may be observable during a ment 8, and projecting towards segment 9. short visit. Males are usually brightly coloured and often have conspicuous markings on the Tropical dragonflies wings. Females are usually dark or brownish In both their ecology and behaviour, yellow and less colourful. tropical dragonflies deviate in some ways Body and wing measurements may help from temperate species. In montane regions to distinguish between similarly coloured isolation processes have favoured speciation, species of different sizes. The body and and diversity in the tropics by far exceeds the abdomen sizes given in this booklet include number of species in temperate regions. In the caudal appendages. Values given are the tropics, manifold niches have enabled the either means of several individuals, or meas - development of specialised life strategies. urements of single individuals. Individual The larvae of Neotropical Pseudostigmatidae variation in body proportions can be up to and some other families, for example, inhab - several millimetres, and this should be borne it ‘phytotelmata’ - water-filled cavities like in mind when comparing observed dragon - tree holes or plant tanks. The long abdomen flies with the values given in the description. of Pseudostigmatidae females is useful for Measures of size and body parts account for oviposition into such deep structures. The both sexes if not indicated otherwise. strategy of migrating species such as Pantala The abundances of species are given for the flavescens may be linked to the unstable and region around La Gamba, and do not apply unpredictable availability of breeding waters to their frequencies in Costa Rica or Central in drier regions. This circumtropical species America. often forms swarms of hundreds of thou -
11 sands of individuals migrating over long dis - Austria (77 species) and Europe (125 tances in front of rain fronts. The eggs are species), Costa Rica is very rich in dragon - laid in bodies of water that sometimes persist flies, with 268 currently described species. no longer than a month. This becomes possi - Many of these dragonflies are part of the ble due to the speed of embryonic and larval North and South American fauna, but a development. In tropical montane forests, small but significant proportion of Costa turbulent and shaded streams harbour a rich Rican dragonflies are endemic to the region, dragonfly fauna. In temperate regions, in which includes Nicaragua and Panama. Cora contrast, relatively few species are adapted semiopaca , a species present in La Gamba, is to these special conditions. endemic to Costa Rica. The Caribbean slope The dragonfly fauna of Costa Rica is one of the Cordillera seems to harbour more of the best-studied in Central America, yet it species. is still not fully explored. In comparison with Odonatological field trips around La Gamba
Although dragonflies are often seen fly - Forests ing or resting on vegetation beside water, the Forests may originally have been the pri - easiest way to observe them is at their breed - mary habitat of dragonflies in Costa Rica, ing sites, usually streams or ponds. and the prevailing conditions may have Odonatological field trips therefore concen - influenced the mixture of species living in trate on aquatic habitats, but these habitats them. Swamps and smaller streams can be are embedded in a matrix of landscapes that completely shaded and flow can be very tur - heavily influence the quality of breeding bulent, which provides well oxygenated sites. Dragonfly distribution is greatly affect - water, but with an increased risk of being ed by the drastic difference between undis - carried away by the water. Polythoridae like turbed forests and intensively used agricul - Cora semiopaca prefer these conditions. The tural areas and their respective water bodies. forest interior, where Mecistogaster modesta
A shaded stream in the forest interior
12 and Megaloprepus cerulatus can be found, is landscapes including plantations, crop fields dark, and temperatures are lower than in and pastures, narrow strips of gallery forest open habitats, constraining the thermal often form the last remnants of primary veg - requirements of adults. Many species living etation. In this dramatically altered land - in the forest are shade–loving and are there - scape, the dragonfly fauna is different, and fore not found in open areas. For a species generalist species like many Libellulidae, like Philogenia zeteki , the dense understorey which are able to live under a wide range of may additionally provide protection from environmental conditions, prevail. On a predators. Such forest species are specialised small spatial scale, species richness can to these circumstances, whereas many other increase in cultivated areas through the species would not be able to survive. Forests colonisation of these habitats by generalists. have been hit hard by human activity, and Mostly, however, generalist species like the remaining islets surrounded by open Erythrodiplax fusca are widespread and com - landscape may be too small or isolated to mon and therefore, on a broader scale, over - sustain populations of forest dragonflies. In all richness may be reduced. forests, on the other hand, degraded and open patches like those caused by tree falls Forest margins or logging, as well as roads, resemble open Aquatic habitats at forest margins can landscapes and are often used by species like either resemble forests or open landscapes Uracis imbuta which are usually found in depending on the type and density of gallery open habitats. vegetation. Running water along forest mar - gins may be suitable for shade–loving Cultivated landscapes species such as Heteragrion erythrogastrum . Cultivated landscapes are those artifi - Artificial ponds can be exposed to the sun cially shaped by human land use. Bodies of and may be colonised by generalist species water in these environments are usually like Orthemis ferruginea . In the garden of the exposed to the sun, leading to higher temper - Research Station, several small ponds and atures and lower oxygen levels. Pollution by rivulets provide habitats for generalists, and the inflow of agrochemicals or domestic some common species can frequently be sewage can influence water quality. observed there. Embedded in a matrix of relatively uniform
Stream with open canopy surrounded by cultivated areas
13 Zygoptera
Family Polythoridae the wings in Polythoridae are petiolate, the (polythorids, polytóridos) wings are relatively narrow, and males lack red colouration at the base. Females are light They are medium–sized Zygoptera species to dark brown. Polythoridae are shade–lov - with dense wing venation, many antenodal ing dragonflies that live beside streams in crossveins, and short legs. In contrast to undisturbed forests. The larvae have lateral members of the Calopterygidae, the bases of gills on the abdomen.
Cora notoxantha common in Central America, but in that size: 39 mm, abdomen: 31 mm, fore wing: 25 mm species the abdomen is almost blue dorsally. The eyes are dark and the face is white. This The thorax of the male is bright yellow or species is known from Costa Rica and blue, with a thin black mid-dorsal line in Panama. some individuals. Blue coloured individuals We found this rare species beside a forest may be confused with Cora marina , a species stream
Cora notoxantha male
14 Cora semiopaca lar. This stream–dwelling species may be size: 35 mm, abdomen: 27 mm, fore wing: 27 mm threatened by disturbance due to its small range size. This stream–dwelling species is endemic to We found this rare species beside a stream Costa Rica. The male has characteristic running through a shaded ravine. reflective zones on the wings, and dark bands on the distal parts of the wings. In the dark forest undestorey, the shimmering blue reflections may attract fe- males that are searching for mat - ing partners and suitable sites for oviposition. The face is white. The female in this photograph was not identified to the species level but is likely to be a female of Cora semiopaca ; most females in the genus look simi - Cora semiopaca male
Cora sp. female
15