Megaloprepus caerulatus
Encyclopedia
Megaloprepus caerulatus is a damselfly
of the Forest Giant family (Pseudostigmatidae
), found in wet and moist forests in Central
and South America
. It has the greatest wingspan
of any living damselfly or dragonfly
, up to 19 centimeters (7.5 inches) in the largest males. Its large size and the markings on its wings make it a conspicuous species; a hovering Megaloprepus has been described as a "pulsating blue-and-white beacon".
As an adult it feeds on orb-weaver spiders in the forest understory, which it plucks from their webs. It lays its eggs in water-filled holes in trees
; males defend the larger holes as breeding territories
. The naiad is a top predator in its tree-hole habitat, feeding on tadpole
s and aquatic insects
, including the larva
e of mosquito
species that are vectors of human disease.
M. caerulatus is the only species in genus Megaloprepus.
. These plant-borne bodies of water, known as phytotelmata, may form in a living tree when a branch breaks off or a burl
rots, or indentations in a trunk may fill with water after the tree falls. The eggs hatch in a minimum of 18 days, but the hatching of eggs laid on the same day is spread out over as much as half a year. This extreme variation in hatching time—unknown in any other damselfly—increases the chance that some eggs will hatch when no predator is present.
As with other damselflies
, the young—known as naiads, nymphs
, or larva
e—are carnivorous. The most ubiquitous prey in the tree holes they inhabit are mosquito
larvae, but they will also feed on tadpole
s, syrphid fly and chironomid fly
larvae, and other odonate
(dragonfly and damselfly) naiads. The three leaflike caudal lamellae at the end of the abdomen, which serve as gill
s, are broad and elaborately folded, an adaptation to intermittent low oxygen
availability in its habitat. Each lamella has a conspicuous white spot, making Megaloprepus easy to distinguish from other tree-hole damselflies.
As many as 13 females may oviposit
in a single large tree hole, laying up to 250 eggs each, but the numbers of naiads are reduced by cannibalism
. Even when there is a high concentration of other prey, Megaloprepus naiads still kill each other until a density of one naiad per 1-2 liter
s of water is reached. They are not territorial, but larger individuals displace smaller ones; their aggressive behavior includes raising and swinging the caudal lamellae and striking with the labium, the hinged, extensible lower "lip" that odonate naiads use to catch prey.
(transparent), with a dark blue band on the outer third. Females have a milky-tinged patch at the tip of each wing, while males of most populations have a white band just inside the blue one.
In 1923, Philip Calvert described Megaloprepus in flight:
It is one of the few species in order Odonata
in which males are larger than females, with abdomens up to 10 cm (4 in.) long and wingspans of up to 19 cm (7.5 in.)—the greatest wingspan of all odonates. Size varies geographically; Megaloprepus on Barro Colorado Island
in Panama are smaller than those at La Selva Biological Station in Costa Rica
or Los Tuxtlas
field station in the Mexican state of Veracruz
.
Adult lifespans as long as 7 months have been recorded.
damselflies, Megaloprepus feeds on web-building spider
s. It forages in areas that receive direct sun, such as the gaps created by fallen trees or branches; the light helps it avoid becoming entangled. When it finds a web, it hovers in front of it until it locates the spider. Then it flies backward and quickly darts forward again to grab the spider in its forelegs. Finally it backs away and perches to consume the spider, removing the legs before eating the body.
, mating with females who come to the tree hole to oviposit
.
Several factors make large tree holes more valuable to Megaloprepus than small ones. Not only can their greater volume accommodate more naiads at a time, they have a higher density of prey in the form of tadpoles and mosquito larvae; this allows the naiads to grow more rapidly and reach adulthood sooner. In forests with a dry season, larger tree holes can last nearly a month longer before drying out completely. As a result, large tree holes can produce three cohorts per season, totalling perhaps a few dozen new adults, while only one or two emerge from a small hole. Large tree holes also give Megaloprepus better chances of surviving to emerge if one of its slower-growing relatives in genus Mecistogaster
is already present. In a tree hole small enough to be effectively patrolled by a single naiad, the first species to hatch is likely to eat all newcomers, but in a large one Megaloprepus can escape long enough to outgrow and eventually eat an older resident. Finally, probably due to the greater abundance of prey, larger tree holes produce larger males that will be better able to defend a territory themselves when they reach reproductive maturity.
A territorial male drives away other males from his territory by chasing and sometimes hitting them. He does not allow females to lay eggs in the hole he defends without mating with him first, but he does not pursue females who opt instead to leave the scene. The structure of the penis suggests that, as with many other odonates
, male Megaloprepus are able to displace sperm from previous matings, ensuring the paternity of the eggs. For their part, females do not choose mates based on size, and will sometimes remate with smaller males who cannot take over a territory and instead adopt a satellite position nearby. At least some females will lay eggs in undefended tree holes before mating again.
ability, making it particularly vulnerable to habitat fragmentation
. While it can breed in secondary forest
, it is less common there than in old-growth forest, even when the two are adjacent. Since Megaloprepus reduces the number of adult mosquito
es that emerge from tree holes it inhabits, and some of the species it preys on are important disease vectors, its conservation may have human health implications.
Damselfly
Damselflies are insects in the order Odonata. Damselflies are similar to dragonflies, but the adults can be distinguished by the fact that the wings of most damselflies are held along, and parallel to, the body when at rest...
of the Forest Giant family (Pseudostigmatidae
Pseudostigmatidae
Pseudostigmatidae is a family of tropical damselflies, known as helicopter damselflies, giant damselflies or Forest Giants. The family includes the largest of all damselfly species...
), found in wet and moist forests in Central
Central America
Central America is the central geographic region of the Americas. It is the southernmost, isthmian portion of the North American continent, which connects with South America on the southeast. When considered part of the unified continental model, it is considered a subcontinent...
and South America
South America
South America is a continent situated in the Western Hemisphere, mostly in the Southern Hemisphere, with a relatively small portion in the Northern Hemisphere. The continent is also considered a subcontinent of the Americas. It is bordered on the west by the Pacific Ocean and on the north and east...
. It has the greatest wingspan
Wingspan
The wingspan of an airplane or a bird, is the distance from one wingtip to the other wingtip. For example, the Boeing 777 has a wingspan of about ; and a Wandering Albatross caught in 1965 had a wingspan of , the official record for a living bird.The term wingspan, more technically extent, is...
of any living damselfly or dragonfly
Odonata
Odonata is an order of insects, encompassing dragonflies and damselflies . The word dragonfly is also sometimes used to refer to all Odonata, but the back-formation odonate is a more correct English name for the group as a whole...
, up to 19 centimeters (7.5 inches) in the largest males. Its large size and the markings on its wings make it a conspicuous species; a hovering Megaloprepus has been described as a "pulsating blue-and-white beacon".
As an adult it feeds on orb-weaver spiders in the forest understory, which it plucks from their webs. It lays its eggs in water-filled holes in trees
Tree hole
Tree hole may refer to:*A tree hollow, a natural cavity in a tree.*A tree throw, a cavity left in the soil after a tree has fallen or otherwise been removed.*A tree mould hole, Formed by lava burning out the tree but retaining the exterior shape and form....
; males defend the larger holes as breeding territories
Territory (animal)
In ethology the term territory refers to any sociographical area that an animal of a particular species consistently defends against conspecifics...
. The naiad is a top predator in its tree-hole habitat, feeding on tadpole
Tadpole
A tadpole or polliwog is the wholly aquatic larval stage in the life cycle of an amphibian, particularly that of a frog or toad.- Appellation :...
s and aquatic insects
Aquatic insects
Aquatic insects live some portion of their life cycle in the water. They feed in the same ways as other insects. Some diving insects, such as predatory diving beetles, can hunt for food underwater where land-living insects cannot compete.-Breathing:...
, including the larva
Larva
A larva is a distinct juvenile form many animals undergo before metamorphosis into adults. Animals with indirect development such as insects, amphibians, or cnidarians typically have a larval phase of their life cycle...
e of mosquito
Mosquito
Mosquitoes are members of a family of nematocerid flies: the Culicidae . The word Mosquito is from the Spanish and Portuguese for little fly...
species that are vectors of human disease.
M. caerulatus is the only species in genus Megaloprepus.
Egg and naiad
Megaloprepus lays its eggs in the water that collects in holes in treesTree hole
Tree hole may refer to:*A tree hollow, a natural cavity in a tree.*A tree throw, a cavity left in the soil after a tree has fallen or otherwise been removed.*A tree mould hole, Formed by lava burning out the tree but retaining the exterior shape and form....
. These plant-borne bodies of water, known as phytotelmata, may form in a living tree when a branch breaks off or a burl
Burl
A burl or bur or burr is a tree growth in which the grain has grown in a deformed manner. It is commonly found in the form of a rounded outgrowth on a tree trunk or branch that is filled with small knots from dormant buds.A burl results from a tree undergoing some form of stress. It may be caused...
rots, or indentations in a trunk may fill with water after the tree falls. The eggs hatch in a minimum of 18 days, but the hatching of eggs laid on the same day is spread out over as much as half a year. This extreme variation in hatching time—unknown in any other damselfly—increases the chance that some eggs will hatch when no predator is present.
As with other damselflies
Damselfly
Damselflies are insects in the order Odonata. Damselflies are similar to dragonflies, but the adults can be distinguished by the fact that the wings of most damselflies are held along, and parallel to, the body when at rest...
, the young—known as naiads, nymphs
Nymph (biology)
In biology, a nymph is the immature form of some invertebrates, particularly insects, which undergoes gradual metamorphosis before reaching its adult stage. Unlike a typical larva, a nymph's overall form already resembles that of the adult. In addition, while a nymph moults it never enters a...
, or larva
Larva
A larva is a distinct juvenile form many animals undergo before metamorphosis into adults. Animals with indirect development such as insects, amphibians, or cnidarians typically have a larval phase of their life cycle...
e—are carnivorous. The most ubiquitous prey in the tree holes they inhabit are mosquito
Mosquito
Mosquitoes are members of a family of nematocerid flies: the Culicidae . The word Mosquito is from the Spanish and Portuguese for little fly...
larvae, but they will also feed on tadpole
Tadpole
A tadpole or polliwog is the wholly aquatic larval stage in the life cycle of an amphibian, particularly that of a frog or toad.- Appellation :...
s, syrphid fly and chironomid fly
Chironomidae
Chironomidae are a family of nematoceran flies with a global distribution. They are closely related to the Ceratopogonidae, Simuliidae, and Thaumaleidae...
larvae, and other odonate
Odonata
Odonata is an order of insects, encompassing dragonflies and damselflies . The word dragonfly is also sometimes used to refer to all Odonata, but the back-formation odonate is a more correct English name for the group as a whole...
(dragonfly and damselfly) naiads. The three leaflike caudal lamellae at the end of the abdomen, which serve as gill
Gill
A gill is a respiratory organ found in many aquatic organisms that extracts dissolved oxygen from water, afterward excreting carbon dioxide. The gills of some species such as hermit crabs have adapted to allow respiration on land provided they are kept moist...
s, are broad and elaborately folded, an adaptation to intermittent low oxygen
Oxygen
Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...
availability in its habitat. Each lamella has a conspicuous white spot, making Megaloprepus easy to distinguish from other tree-hole damselflies.
As many as 13 females may oviposit
Oviposition
Oviposition is the process of laying eggs by oviparous animals.Some arthropods, for example, lay their eggs with an organ called the ovipositor.Fish , amphibians, reptiles, birds and monetremata also lay eggs....
in a single large tree hole, laying up to 250 eggs each, but the numbers of naiads are reduced by cannibalism
Cannibalism
Cannibalism is the act or practice of humans eating the flesh of other human beings. It is also called anthropophagy...
. Even when there is a high concentration of other prey, Megaloprepus naiads still kill each other until a density of one naiad per 1-2 liter
Litér
- External links :*...
s of water is reached. They are not territorial, but larger individuals displace smaller ones; their aggressive behavior includes raising and swinging the caudal lamellae and striking with the labium, the hinged, extensible lower "lip" that odonate naiads use to catch prey.
Adult
The adult's body is dark brown or black and has yellowish markings. The wings are hyalineHyaline
The term hyaline denotes a substance with a glass-like appearance.-Histopathology:In histopathological medical usage, a hyaline substance appears glassy and pink after being stained with haematoxylin and eosin — usually it is an acellular, proteinaceous material...
(transparent), with a dark blue band on the outer third. Females have a milky-tinged patch at the tip of each wing, while males of most populations have a white band just inside the blue one.
In 1923, Philip Calvert described Megaloprepus in flight:
When flying the four wings are spread quite far apart, fore and hind wing of the same side far apart, body horizontal. Flight slow enough so that the movements of each separate wing can be seen—insect consequently moves slowly but can dodge. Mr. Barnes compared the movements of the wings to that of a windmill, but the revolving movements are lacking; I should say the effect produced by the wings is more like that of a jumping-jackJumping jack (toy)The jumping-jack is a toy whose origins date back thousands of years. The jointed jumping-jack figure is a cross between a puppet and a paper doll. The figures are generally made from wood. Their limbs are jointed and tied to a pull string...
with moveable arms and legs pulled by one string, rather slowly, but, of course, at regular intervals.
It is one of the few species in order Odonata
Odonata
Odonata is an order of insects, encompassing dragonflies and damselflies . The word dragonfly is also sometimes used to refer to all Odonata, but the back-formation odonate is a more correct English name for the group as a whole...
in which males are larger than females, with abdomens up to 10 cm (4 in.) long and wingspans of up to 19 cm (7.5 in.)—the greatest wingspan of all odonates. Size varies geographically; Megaloprepus on Barro Colorado Island
Barro Colorado Island
Barro Colorado Island is located in the man-made Gatun Lake in the middle of the Panama Canal. The island was formed when the waters of the Chagres River were dammed to form the lake. When the waters rose, they covered a significant part of the existing rainforest, and the hilltops remained as...
in Panama are smaller than those at La Selva Biological Station in Costa Rica
Costa Rica
Costa Rica , officially the Republic of Costa Rica is a multilingual, multiethnic and multicultural country in Central America, bordered by Nicaragua to the north, Panama to the southeast, the Pacific Ocean to the west and the Caribbean Sea to the east....
or Los Tuxtlas
Los Tuxtlas
The Los Tuxtlas region, very broadly, occupies parts of south central Veracruz, in east central Mexico. The region includes the Sierra de Los Tuxtlas and stretches from Laguna Alvarado, along the Gulf of Mexico, to Laguna del Ostión, then along the westernmost tributaries of Laguna del Ostión, to...
field station in the Mexican state of Veracruz
Veracruz
Veracruz, formally Veracruz de Ignacio de la Llave officially Estado Libre y Soberano de Veracruz de Ignacio de la Llave , is one of the 31 states that, along with the Federal District, comprise the 32 federative entities of Mexico. It is divided in 212 municipalities and its capital city is...
.
Adult lifespans as long as 7 months have been recorded.
Foraging
Like other pseudostigmatidPseudostigmatidae
Pseudostigmatidae is a family of tropical damselflies, known as helicopter damselflies, giant damselflies or Forest Giants. The family includes the largest of all damselfly species...
damselflies, Megaloprepus feeds on web-building spider
Spider
Spiders are air-breathing arthropods that have eight legs, and chelicerae with fangs that inject venom. They are the largest order of arachnids and rank seventh in total species diversity among all other groups of organisms...
s. It forages in areas that receive direct sun, such as the gaps created by fallen trees or branches; the light helps it avoid becoming entangled. When it finds a web, it hovers in front of it until it locates the spider. Then it flies backward and quickly darts forward again to grab the spider in its forelegs. Finally it backs away and perches to consume the spider, removing the legs before eating the body.
Reproduction
Most tree holes contain less than a liter of water, but some can hold as much as 50 liters. Male Megaloprepus defend these larger holes as breeding territoriesTerritory (animal)
In ethology the term territory refers to any sociographical area that an animal of a particular species consistently defends against conspecifics...
, mating with females who come to the tree hole to oviposit
Oviposition
Oviposition is the process of laying eggs by oviparous animals.Some arthropods, for example, lay their eggs with an organ called the ovipositor.Fish , amphibians, reptiles, birds and monetremata also lay eggs....
.
Several factors make large tree holes more valuable to Megaloprepus than small ones. Not only can their greater volume accommodate more naiads at a time, they have a higher density of prey in the form of tadpoles and mosquito larvae; this allows the naiads to grow more rapidly and reach adulthood sooner. In forests with a dry season, larger tree holes can last nearly a month longer before drying out completely. As a result, large tree holes can produce three cohorts per season, totalling perhaps a few dozen new adults, while only one or two emerge from a small hole. Large tree holes also give Megaloprepus better chances of surviving to emerge if one of its slower-growing relatives in genus Mecistogaster
Mecistogaster
Mecistogaster is a genus of large Neotropical damselflies in the family Pseudostigmatidae. It contains the following species:*Mecistogaster amalia - Amalia Helicopter*Mecistogaster amazonica *Mecistogaster asticta...
is already present. In a tree hole small enough to be effectively patrolled by a single naiad, the first species to hatch is likely to eat all newcomers, but in a large one Megaloprepus can escape long enough to outgrow and eventually eat an older resident. Finally, probably due to the greater abundance of prey, larger tree holes produce larger males that will be better able to defend a territory themselves when they reach reproductive maturity.
A territorial male drives away other males from his territory by chasing and sometimes hitting them. He does not allow females to lay eggs in the hole he defends without mating with him first, but he does not pursue females who opt instead to leave the scene. The structure of the penis suggests that, as with many other odonates
Odonata
Odonata is an order of insects, encompassing dragonflies and damselflies . The word dragonfly is also sometimes used to refer to all Odonata, but the back-formation odonate is a more correct English name for the group as a whole...
, male Megaloprepus are able to displace sperm from previous matings, ensuring the paternity of the eggs. For their part, females do not choose mates based on size, and will sometimes remate with smaller males who cannot take over a territory and instead adopt a satellite position nearby. At least some females will lay eggs in undefended tree holes before mating again.
Conservation
Megaloprepus avoids flying across large clearings that lack shaded perches, and has poor flight endurance, achieving a maximum distance of less than 1 km when experimentally released over water. This may limit its dispersalBiological dispersal
Biological dispersal refers to species movement away from an existing population or away from the parent organism. Through simply moving from one habitat patch to another, the dispersal of an individual has consequences not only for individual fitness, but also for population dynamics, population...
ability, making it particularly vulnerable to habitat fragmentation
Habitat fragmentation
Habitat fragmentation as the name implies, describes the emergence of discontinuities in an organism's preferred environment , causing population fragmentation...
. While it can breed in secondary forest
Secondary forest
A secondary forest is a forest or woodland area which has re-grown after a major disturbance such as fire, insect infestation, timber harvest or windthrow, until a long enough period has passed so that the effects of the disturbance are no longer evident...
, it is less common there than in old-growth forest, even when the two are adjacent. Since Megaloprepus reduces the number of adult mosquito
Mosquito
Mosquitoes are members of a family of nematocerid flies: the Culicidae . The word Mosquito is from the Spanish and Portuguese for little fly...
es that emerge from tree holes it inhabits, and some of the species it preys on are important disease vectors, its conservation may have human health implications.