Water boatmen are a natural part of most freshwater ecosystems, but their sudden appearance in large numbers in aquatic environments, such as ponds or swimming pools, often signals an imbalance. Managing their population requires correctly identifying the species and implementing long-term habitat modifications. These modifications target their food source and preference for specific water conditions.
Knowing Your Target: Water Boatmen vs. Backswimmers
The term “water boatman” describes two distinct types of aquatic insects, and knowing the difference is the first step toward effective control. True water boatmen belong to the family Corixidae, while the backswimmer, often confused with them, belongs to the family Notonectidae. The distinction is based on their appearance and behavior, particularly how they swim.
Corixidae, the true water boatmen, are generally flattened and swim right-side up, using their long hind legs like oars. They are mostly harmless, feeding primarily on algae, plant detritus, and microscopic organisms. This diet makes them beneficial for controlling algae growth. In contrast, backswimmers (Notonectidae) are easily identified because they swim upside down, with their belly facing the surface.
Backswimmers have a streamlined, convex body shape and are predatory, using sharp, piercing mouthparts to attack other insects, tadpoles, and small fish. Backswimmers can inflict a painful, stinging “bite” on humans if handled, which is actually a stab with their proboscis. Their presence in a pool or pond often indicates that a food source, such as Corixidae or other small insects, is already established.
Controlling the Environment Through Habitat Modification
The most sustainable way to manage water boatmen and backswimmers is to make the aquatic environment less hospitable. This strategy focuses on removing their food and preferred breeding sites. For Corixidae, this means eliminating the algae and organic debris they feed on. For Notonectidae, this means removing the smaller insects they prey upon.
Improving water quality is paramount, focusing on preventing stagnation and boosting dissolved oxygen levels. Installing an aeration system, such as a fountain or a bottom-diffused aerator, disrupts the water surface and promotes the growth of beneficial aerobic bacteria. These bacteria break down organic sludge and excess nutrients that fuel algae growth, thereby starving the Corixidae.
Regular maintenance, including the prompt removal of fallen leaves, grass clippings, and other organic debris, prevents the accumulation of sludge. If constructing or renovating a pond, grade the banks to a steep slope (ideally a 3:1 ratio). Ensuring the water body is at least three feet deep in some areas will discourage the growth of shallow-water vegetation where these insects cling and lay eggs. Utilizing beneficial bacteria products can also help maintain a balanced ecosystem by consuming excess nutrients and organic waste.
For swimming pools, habitat modification centers on chemical balance. Water boatmen are attracted to pools with existing algae growth, even microscopic amounts. Maintaining a proper free chlorine level and utilizing an algaecide removes the primary food source of the Corixidae. This action, in turn, causes the predatory backswimmers to leave in search of food.
Direct Removal Strategies
When a population is established, especially in a pool, direct removal methods provide immediate relief. Physical removal is the simplest and safest approach, particularly for biting backswimmers. Use a fine-mesh skimming net to actively scoop the insects from the surface and sub-surface of the water.
A temporary disruption of the water’s surface tension is a non-chemical method for immediate control in pools. Applying a small amount of a surfactant, such as diluted liquid dish soap or a commercial surface film product, reduces the water’s surface tension. Since both water boatmen and backswimmers rely on surface tension to breathe or rest, this action causes them to sink and drown. This method requires immediate follow-up skimming or vacuuming to remove the dead insects.
Introducing biological controls is a long-term, self-sustaining strategy for natural ponds. Fish species with large mouths, such as bluegill, sunfish, and trout, readily prey upon the immature and adult stages of both insects. Small fish, including minnows, consume the smaller water boatmen, which helps break the food chain that attracts the larger, predatory backswimmers.