Water Boatman

Water boatman is the common name used for the insects belonging to the true bug family Corixidae. They are also known as Corixids. The name water boatman came from the US due to their boat-like flattened shape. The adult's body can reach up to a length of 3mm-12mm and greyish. The giant water boatman may be of 15-18 mm size maximum. The body is slender and oval. The head is broad and has large eyes with a conical beak. The front legs of the adult Corixids are flattened and short, middle legs are slender in shape, and hind legs have a characteristic oarlike shape. The hind legs are fringed and have tiny hairs, which help in swimming.

They are found in a wide variety of water ecosystems. Water boatman insects are most commonly found in ponds or lakes. However, some species live in brackish water. It is a unique family under the order Hemiptera because they are not predatory. Corixids feed mainly on algae. They have broad beaks, which allows them to swallow solid foods, unlike other true bugs who ingest only liquid.

Taxonomical Classification

The hierarchical taxonomic classification of the water boatman is as follows: -

Kingdom – Animalia

Phylum – Arthropoda

Class – Insecta

Order – Hemiptera 

Sub-order – Heteroptera

Family – Corixidae

Genus: There are almost 33 genera of Corixidae known worldwide.

Species: There are a total of 525 species of water boatman. Of 525 species, 132 species are found in North America. One of the notable species is the lesser water boatman.

Food Habit

Most of the aquatic hemipterans are predatory. However, the true aquatic bugs belonging to the Corixidae family are non-predatory. 

They are the primary consumers in the water ecosystem and feed on aquatic plants and algae. They use their fringed front legs to scoop the algae. They have a broad mouth with straw-like mouthparts. They use the sucking-type mouthparts to inject an enzyme into the plants. These enzymes digest the plants and convert them into easily ingestible fluids. The liquefied material is then sucked through the mouthpart and goes into the digestive tract for further breakdown.

Most of them depend on plants' debris or algae for their food, but some species also feed on small invertebrates. Lesser water boatman is an example of a predatory boatman insect that may feed some small aquatic animal species and aquatic plants.

Distribution

They are found in a wide variety of climatic conditions. North America has a high species richness of water boatmen. There are 123 species of corixids found in North America. They are found in high-altitude places like the Himalayas to the lowest places present in the Death Valley. 

They are primarily found in ponds and lakes where they can cling to some vegetation. Some species also exist in the Brackish waters. 

Corixids are highly attracted to night lights. Most of the species of Water boatman bug is an excellent flier and fly towards the light source during the night.

General Features

The body is oval, elongated and dorsally flattened in shape. The colour of the body varies from black to brown, with lateral cross-lines all over the back of the body. Most of the species are not predatory and eat plant debris or algae. They don't bite humans and are harmless insects to them.

There are three pairs of legs. Two pairs of rear legs are long and robust. One pair of the front legs is short. The front legs are useful for scooping the algae and make it easy to ingest. The hind legs have characteristic oar-like shaped tarsi, which helps in swimming.

The adult's body length varies from 3 mm to 12 mm. They are found floating on the water surface or clinging to the algae. Adults are good fliers and have strong wings. They are generally lighter than water and float on the water or remain attached to some plant debris or algae for support. They move with strong jerking movements.

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Like any other aquatic bug, the water boatman insect also lacks functional gills. They fulfil their oxygen demand by directly taking in air from the atmosphere. They often remain attached to an air pouch or air bubble so that they don't have to swim to the surface frequently for air.

The males and females are morphologically alike. They are dioecious organisms which means that they have separate males and females. However, the males produce a chirping-like sound to attract the females for mating. This process is known as stridulation. 

As we have known from the general features, these boatman bugs are non-predatory and eat the plant materials for survival. The prehensile organ is the scoop-like forelegs. They are short and efficient in scooping out algae and make it easier to eat. The tube-like mouthparts are used to inject an enzyme into the algae for extracellular digestion. These enzymes convert the complex materials into a liquefied substance that is easy to ingest. 

After ingestion, it moves to the digestive tract for a further breakdown of the materials. Digestion is followed by absorption of nutrients and excretion of waste products.

Mechanism of Breathing

The water boatman, due to its lightweight, floats on the water. It may cling to a mass of vegetation at a depth of the water bodies also. 

Like any other aquatic bug, they lack gills too. They come to the surface to breathe in fresh air or breathe through an air layer enveloped around its body and below the wings.

Inspiration of oxygen is carried out from the air bubble enveloped around it. The oxygen which is consumed is replaced by the oxygen dissolved in water by diffusion. The carbon dioxide breathed out by the insect first goes into the air envelope. From here, the carbon dioxide goes out by dissolution into the water.

Life Cycle

The water boatman insect develops into the adult by passing through various developmental stages by incomplete metamorphosis. It takes about six weeks to reach the adult stage from the egg. It acquires the different stages by the process of molting.

There are Three Developmental Stages-

1) Egg –In the summer and spring seasons, the females lay clusters of fertilized eggs on the underwater leaf surfaces or rocks. The eggs remain firmly attached to the surface. The eggs hatch after 1-2 weeks.

2) Nymphs – The nymphs come out after the eggs are hatched. Nymphs somewhat look similar to the adult but lack wings. It goes through five intermediate stages to form instars by the process of molting. 

3) Adults – After molting, the last nymphal stage or instar, the nymphs mature into fully grown winged adults. It takes several weeks to reach the adult stage from the eggs.

Seasonal Adaptations

When the environmental conditions become adverse, they adapt to the environment by hibernating themselves.

Adults hibernate in extreme winters in the mud formed beside the ponds. Sometimes, they even remain active under the ice layers. 

As they are excellent fliers, they fly to larger lakes from smaller water bodies. The more giant lakes do not freeze in the winters, so the water boatman tends to fly to bugger lakes. Spring and summer season is highly suitable for multiplying their generations. Females mostly lay eggs in the summer and spring seasons. 

Ecological Significance

They play a crucial role in the water ecosystems. They act as the connecting link between producers- algae and secondary consumers. The water boatman is the primary consumer. 

As they consume plant debris, small organic matter, and algal matter, they help keep the ponds and lakes clean. There are many water boatman predators of the bug. Frogs, fishes, birds, and higher invertebrates like scorpions and fish are the predators of these species and keep their population under control. They are tiny bugs but have a significant role in maintaining the ecological balance. If the number of Coroxids decreases in the water, then the whole food chain will be disturbed. Many species will start declining due to the absence of food.

Stridulation – A Characteristic Feature of the Water Boatman

The water boatman is dioecious. The males and females are separate but morphologically look similar.

The males make characteristic chirping or squeaking sounds during the mating season. The males have rough edges on the front legs. They rub their forelegs with their heads and produce this unique sound. It is mainly to attract females during mating season. This process of producing sound is known as stridulation. The sound produced by some of the species of water boatman has even bagged world records of highest sound by insects. They can produce the sound of 99 decibels.

Water Boatman and Backswimmers

The backswimmers and water boatman have striking similarities. They look very much alike, and it is often difficult to distinguish them. Backswimmers belong to the family Nectonidae, and water boatman belongs to the family Coroxidae.

Coroxids are harmless to humans, but backswimmers may give a painful bite. Therefore, it is crucial to differentiate between them. The significant difference between these two species is that the Backswimmers are predatory, and water Boatman are generally non-predatory.

Another habitual difference is that the water boatman swims while the dorsal side facing upwards, and Backswimmers swim in an upside-down manner.

Water boatman is an elongated and oval-shaped aquatic bug with a dorsally flattened body belonging to the Coroxidae family. The size ranges from 3mm- 12 mm. They may be black to brown and have parallel cross-lines all over their back.

They are found from the highest elevations like the Himalayas to the lowest parts of the world like the Death Valley. This aquatic bug is mainly found in stagnant water bodies like ponds and lakes. They may also inhabit brackish waters. Water boatman cannot withstand the extreme winter conditions; therefore, he opts for hibernation to escape the low-temperature periods.

There are many water boatman predators like fish, large invertebrates like the scorpion, and frogs. Even humans consume these bugs in some places of Malaysia. 

They breathe through the help of air envelopes around them and below the wings. Also, they may go to the surface to breathe air.

Males have stridulatory organs on their forelegs. They rub their forelegs against the head to produce the characteristic chirping sound to attract the mate. Females lay fertilized eggs in clusters in the spring or summer season. The eggs remain attached to the underwater rocks or vegetation. After going through 3 developmental stages, the eggs convert to mature winged adults after several weeks.