The term “water boatman” refers to a common aquatic insect found in freshwater habitats worldwide, but it is confusing because it encompasses two distinct insect families with dramatically different diets and behaviors. Their feeding habits range from scraping up microscopic organisms to actively hunting small vertebrates. Understanding what these insects eat requires separating these two groups.
Identifying the Two Major Types
The common name “water boatman” applies to two families of insects within the order Hemiptera: Corixidae and Notonectidae. Distinguishing these groups is important, as their ecological roles are opposed.
True Water Boatmen (Corixidae) have a relatively flattened body and swim right-side up, often near the substrate. Their front legs are short and scoop-shaped, which aids in their feeding method. Backswimmers (Notonectidae), by contrast, are easily identified because they swim upside down, with their dorsal side facing the bottom. Their body is convex or triangular, resembling the keel of a boat. They use their long, hair-fringed hind legs like oars to propel themselves rapidly. This difference in swimming posture and physical structure directly correlates with their specialized feeding strategies.
The Diet of True Water Boatmen (Corixidae)
True Water Boatmen (Corixidae) are largely non-predatory, setting them apart from most other aquatic true bugs. Their diet primarily consists of fine organic matter, making them important primary consumers and detritivores. Specific food sources include algae, diatoms, decaying plant matter, and detritus found on the bottom of ponds and streams.
These insects possess specialized mouthparts that facilitate their unique feeding approach. Corixidae have a broad beak, which is unusual for true bugs, allowing them to ingest solid food particles. They use their fringed, scoop-like front legs to stir up fine sediments and microscopic organisms from the substrate.
The scooped material is then ingested and digested. Some species inject enzymes into plant matter to liquefy it before sucking up the resulting fluid. This process establishes their role as recyclers, helping to clean the water environment by breaking down organic debris. The majority rely on this herbivorous and detritivorous diet.
The Diet of Backswimmers (Notonectidae)
Backswimmers (Notonectidae) are active and voracious predators, the complete opposite of True Water Boatmen. They hunt a wide range of aquatic organisms, including mosquito larvae, small aquatic insects, microcrustaceans, small fish, and tadpoles. Their upside-down swimming position allows them to easily detect and ambush prey from below the water surface.
They also routinely prey on terrestrial insects that fall into the water, detecting the vibrations these struggling insects create on the surface tension. Backswimmers use their first and second pairs of legs to grasp and hold their prey firmly. Their feeding is characterized by a sharp, piercing mouthpart, known as a proboscis or beak.
The proboscis is used to pierce the prey’s exoskeleton, after which they inject paralyzing toxins and digestive enzymes. These enzymes liquefy the prey’s internal tissues, allowing the backswimmer to suck out the resulting fluids. Their predatory nature is so effective that they can inflict a painful stab on a human if carelessly handled, a sensation often compared to a bee sting.