Review on Predatory Aquatic insect Backswimmer Notonecta (Hemiptera, notonectidae) species
Annu Kumari
Research Scholar, Jai Prakash University, Chapra, Bihar, India.
*Corresponding Author E-mail: sainiannu6553@gmail.com
Abstract:
Backswimmers, belonging to the family Notonectidae and particularly the genus Notonecta, are key predatory insects found in freshwater habitats across the globe. These insects serve a dual ecological function: they help control mosquito larvae and other aquatic invertebrates, yet they also pose a significant risk to fish seed production by preying on fish eggs, spawn, fry, and fingerlings. This review provides an overview of the taxonomy, morphology, distribution, life cycle, predatory habits, and ecological importance of Notonecta species, with a focus on their effects on aquaculture. Backswimmers have developed impressive adaptations for life in water, such as specialized swimming legs, body hairs that retain air, and effective predatory mouthparts, allowing them to capture and eat a variety of prey. Their predatory success is affected by factors like prey density, prey size, habitat features, and environmental conditions. Numerous studies have reported significant losses of fish larvae due to Notonecta spp., especially in nursery ponds used for cultivating Indian major carps (Catla catla, Labeo rohita, and Cirrhinus mrigala). The review emphasizes the economic impact of backswimmer infestations in aquaculture and explores available management strategies, including selective insecticides and traditional pond management techniques. Gaining insight into the biology and predatory behavior of Notonecta species is crucial for creating effective control methods that reduce fish seed mortality while maintaining beneficial aquatic life. This review offers valuable information for fisheries scientists, aquaculture professionals, and aquatic entomologists engaged in sustainable fish production and aquatic ecosystem management.
KEYWORDS: Backswimmer, Notonecta, Notonectidae, predatory aquatic insects, Fish fry, Aquaculture, Indian major carps, Nursery ponds, Biological interactions.
INTRODUCTION:
The world's insect species include 4% that are aquatic, with these insects undergoing significant morphological changes in water environments during both larval and adult stages. Their diverse adaptations make them fascinating, and many aquatic insects are known to prey on and eliminate carp spawn. The predatory efficiency of aquatic insects against Anophelini and Culicini larvae has been well-documented1,2. Therefore, controlling and eliminating harmful aquatic insects is essential in pond culture, particularly in nursery ponds, as their removal is vital for enhancing fry survival rates3. The previous research4 noted that predation rates increase with higher prey density, as predators consume more when food is abundant.
A significant portion of the nation's agricultural and aquacultural resources is lost due to insect infestations. Predatory aquatic insects have a substantial impact on the growth and survival of fish larvae. Most aquatic insects, whether in larval or adult stages, feed on fish hatchlings or fry and compete with them for food due to their diverse feeding habits. Bugs and beetles are the most prevalent predatory insects5. Beetles such as Cybister, Gyrinus, and Sternolephnus inflict considerable damage on young fish. Aquatic bugs are highly predatory and can harm fingerlings. These predatory insects play a significant destructive role in fish nurseries6. Water scorpions from the genus Laccotrephes and insects from the genus Ranatra are also highly predatory on fish fry.
Backswimmers (Notonectidae), with Anisops as a notable example, are responsible for the most depredations7. Notonectids prey on carp spawn and fry by using their piercing mouthparts to extract body fluids from fish. They inhabit a wide range of freshwater environments8. These predators are relatively large and swim actively. The order Hemiptera includes the family Notonectidae within the section Hydrocorisae. This insect family is sometimes referred to as greater water boatmen or backswimmers. Notonectids, commonly known as backswimmers, are named for their distinctive swimming style, where they move through the water with their bellies facing upwards. Although rare, notonectids can occasionally inflict wounds on humans using their proboscis or mouthparts. These insects are classified as bugs, characterized by their small to medium size and piercing-sucking mouthparts. The term "Water boatmen" is derived from their hind legs, which are adapted for swimming and resemble oars due to the presence of hairs. Notonecta species lay their eggs either in autumn or spring, depending on the species, and they reproduce annually9.
Adult notonectids, generally brown or dull grey, typically measure between 14 and 17 mm in length10. The common backswimmer favors environments rich in vegetation and is frequently located near aquatic plant edges, a preference that persists regardless of its prey selection11. A diverse habitat is ideal for the common backswimmer. They feed on a variety of aquatic organisms, such as Daphnia spp. (water fleas), and are also known to consume fish eggs, fry, and tadpoles12. Notonecta spp. mainly feed on other terrestrial insect species. Studies have indicated that Notonecta glauca targets the larvae of the Culex pipens mosquito13.
Both adult and juvenile Notonecta glauca inhale air rather than depending on dissolved oxygen in water. Their bodies are equipped with hair-like structures known as setae and microtrichia, which facilitate their aquatic life. These hairs cover the entire body of a backswimmer, except for the pronotum (the area behind the head), head, and legs. This layer of hair creates an airtight film that traps air, enabling the insects to absorb oxygen while submerged and keep their bodies dry. The microtrichia's thickness allows the air to be retained for up to 130 days, and this air film appears as a silvery sheen when viewed with the naked eye14. Compared to other Notonecta species, N. glauca extracts food more slowly and is less responsive to surface disturbances. Notonecta spp. are generally found below the water's surface rather than at it. N. glauca remains submerged when the air temperature is below 15°C (59°F) and spends more time on the water surface when temperatures exceed 15°C (59°F). They prefer to stay fully submerged at 5°C (41°F). The common backswimmer tends to remain underwater at higher temperatures15.
Backswimmers, which are also referred to as boat flies or wherrymen, consist of approximately 300 species spread across 10 genera, inhabiting both temperate and tropical regions worldwide. The genus Notonecta includes species that are extensively found in the Palearctic, Neo-arctic, Neo-tropical, African tropical, and Oriental zones. Conversely, the genera Martarega and Buenoa are indigenous to the Western Hemisphere, while Enithares, Nychia, and Anisops species are situated in the Eastern Hemisphere. Other genera, such as Paranisops and Walambi anisops, are located in more restricted areas like Australia, whereas Aphelonecta is found in the Oriental region and Enitharoides in the Neotropical regions15.
3. Development of Notonecta insects:
Aquatic insects are frequently used to evaluate ecosystem health and are vital components of a healthy natural aquatic environment16. The growth of aquatic insects is often linked to the presence of aquatic weeds and an excess of organic matter17. In nursery pond management, heavy fertilization with organic manure before introducing spawn can lead to the emergence of predatory insects. Aquatic predators present a similar threat. In tropical areas, these insects are prevalent for much of the year, especially during and after the rainy season, posing a significant challenge.
4. Predatory efficiency of Notonecta species:
A predator's ability to capture, manage, and consume its prey is greatly affected by the size of the prey relative to the predator. The size ratio between prey and backswimmers likely influences their feeding choices. Backswimmers are known for size-selective predation, consuming a larger share of the largest zooplankton within a species. They prefer larger prey to avoid the challenges associated with capturing and handling smaller prey. As "sit and wait" predators, backswimmers remain suspended in the water column, waiting for prey to approach18. Their specialized binocular-like eyes help them spot and capture prey, and with strong meso-thoracic and pro-thoracic legs, backswimmers can quickly catch and hold live prey, aided by their rapid acceleration. These external feeders use their beaks to pierce their prey, injecting a paralyzing fluid before extracting body fluids19.
The success of aquatic insect predators depends on various factors, such as prey density in the environment, prey size and physiological condition, prey mobility, behavioral adaptations of prey and predators in the same habitat, and the absence of predator detection mechanisms in prey species. Insects can locate prey through different mechanisms, including chemical, tactile, or optical signals, as well as chemically mediated avoidance, a strategy prey use to detect and evade predators. These chemicals, known as semiochemicals, are released by predators into the environment. Prey often uses these substances to recognize the presence of predators and minimize interactions20.
Figure 1: (a) Adult Notonecta sp. (b) Scutellum (c)Vertex and (d) Antenna of Notonecta
Predation of Notonecta spp on Fish:
Backswimmers predominantly consume the spawn and fry stages of commercially valuable fish and tadpoles. Aquatic insects, such as Notonectids and Cybister larvae, frequently found in fish nurseries, are known to prey on the spawn and fry of various culturable fish species. These insects present a considerable threat to fish nurseries in India, where large-scale rearing of Indian major carps, including Catla catla, Labeo rohita, and Cirrhinus mrigala, occurs from spawn to fry21.This was followed by Rohu spawn at 2.19 N/hr, while Catla spawn had the lowest predation rate of 1.38 N/hr at the same density. A decrease in fish survival rate was linked to an increase in Notonecta's predatory efficiency.
The past research22recorded that Notonecta glauca, Acilius sulcatus, Macrodytes marginalis, Anax imperator, and Aeshna uncea destroyed 15 (10.7 mm), 17 (8-17 mm), 14 (21-25 mm), and 51 (10.4 mm) fry, respectively. The past researches23,24 noted that young crayfish are preyed upon by backswimmers. Berezina25 reported that a large population of Notonecta glauca in ponds of about 0.01 ha could kill between 2,500 and 3,500 fish larvae daily. Dahm26 observed that a single adult N. glauca could kill approximately 2.6 fish larvae per day.
Even when younger crayfish are killed by notonectids or resort to cheliped autotomy to escape predators, their individual growth is adversely affected. Yurembam et al.27 indicated that fish, particularly in their larval stages such as spawn, fry, and fingerlings, are vulnerable to aquatic predatory insects (Notonecta, Ranatra, Cybister, Lethocerus, Nepa, Hydrometra, and Belostoma) found in various types of fish ponds, including nursery and stocking areas. The study by Singh et al.28 highlighted the predatory nature of Notonecta spp. in fish ponds, noting that these bugs consume a variety of small creatures such as crustaceans, tadpoles, fish hatchlings, insects, and their larvae. They observed that these highly predatory backswimmers can destroy carp fry measuring 10-13 mm. Gonzalez and Leal12 found that Notonecta spp. exhibited a higher predation rate on fish spawn and fry, tadpoles, and also preyed on other insects.
CONCLUSION:
Backswimmers (Notonecta spp.) are crucial predatory insects found in freshwater environments. Their distinct physical and behavioral traits, such as adept swimming, special mouthparts for piercing and sucking, and advanced prey-detection skills, make them formidable predators. While they play a beneficial role in aquatic ecosystems by controlling mosquito larvae and other invertebrate populations, their predation presents a significant issue for freshwater aquaculture, especially in fish nursery ponds.
Research has shown that Notonecta species can lead to high mortality rates of fish eggs, spawn, fry, and fingerlings, causing notable economic losses during the initial phases of fish seed production. Factors such as prey density, prey size, environmental conditions, and habitat features affect their predatory success. In India and other tropical regions, where Indian major carps are commonly reared in nurseries, backswimmer infestations pose a significant barrier to achieving high fish seed survival rates. Therefore, managing Notonecta populations effectively is crucial for successful aquaculture. Implementing preventive pond management techniques, regular monitoring, removing aquatic weeds, and carefully using selective insecticides can greatly reduce predation while minimizing harm to beneficial aquatic life. Future studies should aim to develop environmentally friendly and species-specific control strategies that maintain the ecological role of backswimmers while safeguarding economically valuable fish stocks.
A thorough understanding of the biology, ecology, distribution, and predatory habits of Notonecta species will aid in better nursery pond management, improved fish seed survival, and sustainable aquaculture growth. This review underscores the need to combine ecological insights with practical management strategies to lessen the negative impacts of predatory aquatic insects in freshwater fish farming systems.
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Received on 13.06.2026 Revised on 29.06.2026 Accepted on 11.07.2026 Published on 14.07.2026 Available online from July 25, 2026 Research J. Science and Tech. 2026; 18(3):279-283. DOI: 10.52711/2349-2988.2026.00039
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