Both the keeled skimmer and the black-tailed skimmer are dragonflies belonging to the family Libellulidae. Dragonflies are insects characterized by their large multifaceted eyes, two pairs of strong transparent wings, and an elongated body. Dragonflies are valuable predators that feed on mosquitoes, flies, butterflies, moths, and other small insects. There are over 5500 species of dragonflies found all over the world except Antarctica.
Dragonflies have a complex life cycle that includes an aquatic larval stage (naiad or nymph) that can last up to several years, followed by metamorphosis into a winged adult that lives near water sources. Dragonfly larvae are voracious predators that help control mosquito and other insect populations. Adult dragonflies continue to feed on flying insects, making them valuable for natural control of insect pests.
Overview of Keeled Skimmers
Keeled skimmers belong to the genus Orthetrum of the skimmer family Libellulidae. There are around 20 known species of keeled skimmers identified so far. They are found throughout the warmer regions of the world, including the Americas, Africa, Asia, Australia, and some Pacific islands.
Some key features of keeled skimmers:
– Medium-sized dragonflies with long, slender abdomens. Adults range from 45-60 mm in length.
– Color patterns consist of black, brown, yellow, or blue. Some species have striped patterns on their thorax and abdomen.
– The most distinctive feature is a keel (ridge) that runs down the top of the abdomen. This is more pronounced in males.
– Large clear wings with dark brown veins and stigmas. Hindwings are often tipped with white or yellow.
– Dark patches at the base of the hindwings are diagnostic for many species.
– Larvae are stocky with short legs and large eyes. They live in muddy bottoms of ponds, lakes, and slow streams.
– Adults are strong fliers and regularly migrate long distances. They are often seen patrolling territories and feeding on the wing.
– Worldwide distribution but prefer warmer climates. Absent from colder regions.
Some well-known keeled skimmer species include the blue-tailed skimmer (Orthetrum glaucum), variable skimmer (Orthetrum internum), and crimson-tailed skimmer (Orthetrum pruinosum). Keeled skimmers are common dragonflies seen near freshwater throughout their range.
Overview of Black-tailed Skimmers
Black-tailed skimmers are very closely related to keeled skimmers but placed in a separate genus Orthetrum. There are only two recognized species:
– Black-tailed skimmer (Orthetrum cancellatum)
– Vermilion-tailed skimmer (Orthetrum chrysis)
Some key features of black-tailed skimmers:
– Very similar to keeled skimmers in size, shape, and habits. Adults 45-65 mm long.
– Abdomens are more robust compared to keeled skimmers. Lack a distinct keel ridge.
– Color patterns are pruinose (have a waxy white or blue powder). Dark metallic green to black overall.
– Distinctive black patches at the base of the hindwings. Abdomen tips are red to yellow.
– Males have red or orange-red color on abdomen. Females are yellow to green.
– Larvae live in muddy pools, ponds, lakes, and slow rivers.
– Adults fly constantly during the day hunting for insect prey. Less territorial compared to keeled skimmers.
– Found in Africa, Middle East, and South Asia west to Greece. Mostly tropical distribution.
The black-tailed skimmer is widespread across Africa while the vermilion-tailed skimmer is found in the Middle East and South Asia. They overlap in range in parts of East Africa.
Differences Between Keeled and Black-tailed Skimmers
While keeled skimmers and black-tailed skimmers look nearly identical, there are some key differences:
Abdomen Shape:
– Keeled skimmers have a distinct ridge (keel) running down the top of the abdomen. This is pronounced in mature males.
– Black-tailed skimmers lack a keel on their abdomen, giving them a more cylindrical, robust shape.
Color Patterns:
– Keeled skimmers exhibit more boldly colored stripes on the thorax and abdomen. Markings are black, yellow, or blue.
– Black-tailed skimmers are mostly pruinose (powdery waxy coating). Dark metallic green to black overall with pale markings.
Wing Markings:
– Keeled skimmers have clear wings with dark veins and stigmas. Variable dark patches at wing bases.
– Black-tailed skimmers have very distinct black patches covering the bases of the hindwings.
Range:
– Keeled skimmers are found worldwide in warmer regions. Absent from colder climates.
– Black-tailed skimmers occur only in Africa, the Middle East, and South Asia. Tropical distribution.
Habitat:
– Keeled skimmers occupy diverse freshwater habitats including lakes, ponds, marshes, rivers, and streams.
– Black-tailed skimmers prefer more stagnant waters like pools, ponds, and lakes. Less common along flowing waters.
Behavior:
– Keeled skimmer males are highly territorial, patrolling and defending prime feeding areas.
– Black-tailed skimmer males show less territoriality and feed more widely over open water.
Taxonomic Classification
Keeled skimmers and black-tailed skimmers belong to the family Libellulidae, the largest family of dragonflies with over 700 species.
Their full taxonomic classification is:
Keeled Skimmers
Kingdom: Animalia
Phylum: Arthropoda
Class: Insecta
Order: Odonata
Suborder: Anisoptera
Family: Libellulidae
Genus: Orthetrum
Black-tailed Skimmers
Kingdom: Animalia
Phylum: Arthropoda
Class: Insecta
Order: Odonata
Suborder: Anisoptera
Family: Libellulidae
Genus: Orthetrum
They are placed in separate genera based on consistent morphological differences, but ongoing genetic analysis may help better resolve their taxonomy. There is still debate whether they warrant separation into two distinct genera.
Life Cycle and Biology
Keeled skimmers and black-tailed skimmers share a similar biological lifecycle typical of dragonflies:
Egg:
– Fertilized eggs are laid singly or in groups in aquatic vegetation or mud. Eggs hatch in 1-4 weeks.
Larva:
– Aquatic nymphs (naiads) are voracious predators that feed on small insects, tadpoles, and minnows. They have a large extendable jaw for capturing prey.
– Larval stage lasts 2-5 years for most species. Molt repeatedly as they grow.
Pupa:
– Final larval molt reveals the winged pupa. Pupal stage lasts just 1-2 weeks.
Adult:
– Metamorphosis emerges as a sexually mature adult dragonfly. Lives near water.
– Excellent fliers that feed on flying insects captured in flight.
– Males are territorial and patrol breeding areas. Females enter only to mate and lay eggs.
– Adults live 2-6 weeks on average. Die shortly after breeding.
Both skimmers have a life span from egg to adult of approximately 2-5 years. The larval stage makes up the majority of their life cycle. Adults live only long enough to reproduce.
Habitat and Distribution
Keeled and black-tailed skimmers occupy similar freshwater habitats but differ in their global distribution:
Keeled Skimmers:
– Found on every continent except Antarctica. Mostly in warmer temperate and tropical regions.
– Occur near all types of freshwater including lakes, ponds, marshes, rivers, streams, and canals.
– Larvae live in muddy or silty bottoms. Tolerant of disturbed and polluted waters.
– Adults often seen perched on shoreline vegetation. Regularly migrate long distances.
Black-tailed Skimmers:
– Restricted to Africa, the Middle East, and South Asia. Occur in the tropics.
– Prefer more stagnant waters like ponds, lakes, and pools. Less common along rivers and streams.
– Larvae inhabit muddy ponds and lakes with rich vegetation.
– Adults fly over open water. Less likely to perch compared to keeled skimmers.
Both skimmers are absent from cooler temperate areas and require warmer conditions to breed and thrive. Their habitat preferences likely help separate their geographic ranges.
Conservation Status
Most keeled skimmer and black-tailed skimmer species are currently not considered threatened:
Keeled Skimmers:
– Classified as Least Concern by the IUCN Red List. Populations appear stable.
– Common and adapt readily to human-altered aquatic habitats.
– Pollution and wetland degradation can cause local declines.
Black-tailed Skimmers:
– Also classified as Least Concern with stable populations.
– Sensitive to water quality decline and wetland loss in parts of range.
– Vermilion-tailed skimmer has restricted habitat but not nearing threatened levels.
Further monitoring is needed for some localized and endemic keeled skimmer species. Overall, both groups are currently not of conservation concern due to their broad distributions and habitat adaptability. Preserving water quality and wetland habitats is still important for population health.
Interactions with Humans
Neither keeled skimmers or black-tailed skimmers are aggressive toward humans. They do not sting, bite, or spread disease. In fact, their predation on mosquitoes and flies makes them beneficial:
– Valued as natural predators of crop and nuisance insect pests. A dragonfly can eat hundreds of insects daily.
– Larvae help control mosquito populations in aquatic habitats.
– Adults eat nuisance flies, gnats, and mosquitoes that bite humans and livestock.
– Dragonflies are sensitive to environmental pollution. Declines signal problems in aquatic systems.
– Considered iconic, beautiful insects. Part of their ecosystems’ biodiversity.
– Used symbolically in art, literature, folklore, and mythology across many cultures.
– Popular subjects for nature photography and insect collecting.
– face threats from wetland development, pollution, and pesticides. Habitat conservation is vital.
With education on their ecological roles, keeled skimmers and black-tailed skimmers can continue thriving alongside human communities into the future through sustainable development practices and habitat preservation. They represent an important linkage between aquatic and terrestrial food chains.
Conclusion
In summary, keeled skimmers and black-tailed skimmers are very closely related dragonflies in the family Libellulidae. While they appear almost identical, keeled skimmers can be distinguished by the ridge on their abdomen, more boldly colored markings, different wing patterns, worldwide distribution, and habits. Black-tailed skimmers lack a keel, have a darker pruinose coloration, limited range in Africa and Asia, and differ in small aspects of habitat and behavior. Both play valuable roles as aquatic predators during their larval stage and continuing as aerial insect hunters as adults. With appropriate habitat conservation, these fascinating dragonflies can persist as important components of freshwater ecosystems and our natural heritage.
