Incredible Creatures: In Golden Pond: Giant Water Bugs and Water Boatmen

Giant Water Bug on parking lot.

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Insects are a vital component of the aquatic environment. Some aquatic insects are valuable predators of other insects. And many fish and water birds rely on insects for food. In this months Incredible Creatures we will explore the amazing world of two very different true bugs that live in the water. One is an important source of food for fish, while the other can catch and eat small fish. One plays music, the other has some interesting parental methods. And both are a source of food in some parts of the world. Welcome to the world of giant water bugs and water boatmen.

Bugs are real suckers

To many people the word “bug” refers to any insects. But technically this is not correct. Within the insects, their is a group (order) called Hemiptera which are referred to as the true bugs. Confused? So a ladybug, although an insect, is not a true bug (it is a beetle), but a stink bug is a true bug. So what defines a true bug? One of the features is that they are all real suckers. This doesn’t mean that they will fall for your pranks every time, but that true bugs all have mouthparts like a thin straw for sucking up fluids. They feed on things like other insects and plants, and have developed ways of making a good drink out of these things.

Giant Water Bugs

Giant water bugs are aquatic insects that belong to the family Belostomatidae. They are the largest of the true bugs. There are about 170 species of giant water bugs worldwide, generally divided into 2 groups, or subfamilies. In almost all species the front legs are modified into raptorial appendages used to grab prey. The exception being an African species that eats snails and has normal front legs.

Giant water bugs feed on aquatic invertebrates, snails, crustaceans, amphibians, and can feed on small fish. Some of the largest species have also been found to capture and feed on water snakes. There is a cool YouTube video called “Giant Water Bug Attacks and Kills a Snake” for those who like watching nature in action. They often lie motionless under the water, attached to various objects, where they wait for prey to come near. They then strike, injecting a venomous digestive saliva with their beak (which in true bugs is called a rostrum). They then suck out the liquefied remains.

Some species of giant water bugs can fly, and do so at night. They can be disoriented by artificial sources of light, and end up in areas where they naturally would not occur, such as below lights on roads, parking lots, etc. Although they look intimidating, they will not hurt you, unless possibly you try to handle them and startle them. For humans, the bite from a giant water bug would be painful, but of no medical significance. Occasionally, when encountered by a larger predator, such as a human, they have been known to “play dead” and most species can emit a fluid from their anus.

Giant water bugs show paternal care for their young, where the males are involved in the parenting. In species of the subfamily Belostomatinae, the eggs are typically laid on the male’s wings and carried until they hatch. In the subfamily Lethocerinae, the eggs are laid on emergent vegetation and guarded by the male.

There’s a Bug on my Plate! And it’s tasty!

Giant water bugs are a popular food in parts of southern Asia, such as Vietnam, Thailand, Cambodia, Laos and the Philippines, and can be found for sale in markets. They are often fried or roasted. It is usually the species Lethocerus indicus that is used. The taste of the flight muscles is often compared to sweet scallops or shrimp. The “essence” of the giant water bug is also collected. A pheromone produced by the male to attract the female is harvested by collecting its liquid-producing sacs. That liquid is then placed in small glass containers. It is used by adding drops to dipping sauces or soups. Most of the essence on the market is imitation, and the real stuff fetches a high price.

Giant water bugs are sometimes collected for eating using large floating traps on ponds, set with black lights to attract the bugs. Adults flying at night are attracted to lights during the breeding season.

Water Boatmen

Water boatmen are aquatic true bugs that belong to the family Corixidae. There are about 500 species worldwide. Their two pairs of hindmost legs are long. The last pair of legs have the final segment covered with hairs and is scoop- or oar-shaped, which helps with swimming. Hence the name “water boatman”.  The front pair of legs are short. Some water boatmen species are able to produce a squeaking sound by rubbing the front legs against the head (stridulation). The sound is used to attract mates.

Water boatmen live in slow rivers and ponds, and can sometimes be found in household pools or birdbaths. They have wings, sometimes fly at night, and can be attracted to artificial lights. I sometimes get them coming to the black (ultra violet) collecting light I set up over a sheet in our backyard. The pair in the photo was captured this way. They feed on aquatic plants and algae. But when you only have what looks like a thin straw for mouthparts, you can’t just bite off a chunk of plant. What water boatmen do is first use their straw-like mouthparts to inject enzymes into plants. The enzymes digest the plant material, letting the insect suck the liquified food back through its mouthparts and into its digestive tract.

Water boatmen lay their eggs on submerged plants, sticks, or rocks. In waters without many places to lay their eggs, every bit of available good egg laying site may be covered in eggs. The eggs are food for fish and water birds. And people have figured out ways of harvesting water boatmen eggs for food.

Having Your Cake, and Eating Bugs too!

In Mexico, the eggs of water boatmen are prepared and eaten in a variety of ways. One example is to use a flour made from the eggs to make a cake called hautle. Water boatmen are relatively small aquatic insects. So how would you get enough eggs from these bugs to make an egg cake? These insects are abundant in lakes near Mexico City and other areas. Bundles of rushes that are attractive to egg-laying females are placed in the water, and after some weeks are removed, dried, and beaten on cloths to separate the eggs. The eggs are then cleaned, sifted, and ground into a flour that is used to make the cakes known as hautle.

There are many other types of true bugs that live in or on the water, such as water striders, water treaders, backswimmers, etc. And then there many different types of aquatic beetles, dragonfly and damselfly larvae, mayflies, caddisflies, stoneflies, and many others. Whether predator or prey, eating algae or keeping our game-fish fed, each has their role in helping our waters achieve a gold standard.

Incredible Creatures is a monthly contribution to provide information on some of the common yet often not well known creatures that we share space with in Manitoba and abroad.  

Water Boatmen from black light sheet.