Roach, also known as a cockroach, and a water bug are two distinct species of insects. However, the brownish colour of the two insects creates an element of confusion.
Roach vs Water bug
The difference between a roach and a waterbug is that the size of a cockroach’s antenna is larger than that of a water bug’s antenna. In addition, cockroaches have flat, oval, and slim bodies. On the other hand, a water bug has a large and round body with flattened legs. The size of a cockroach ranges from ½ to 2 inches. In contrast, the size of a water bug ranges from 2 to 4 inches.

A cockroach is an insect with a brownish colour. It belongs to the order Blattodea. Cockroaches have a round body shape. This insect is the most active at night time.
A water bug is an insect with a long and round body. It belongs to the order Hemiptera. They are aquatic insects and usually reside in wet sewers, basements, slow-moving pools, freshwater ponds, and marshes.
Comparison Table
Parameters of Comparison | Roach | Water Bug |
---|---|---|
Definition | Roach is an insect species belonging to the order Blattodea. | Water bug is an insect species belonging to the order Hemiptera. |
Size | ½ inches to 2 inches | 2 to 4 inches |
Habitat | Cockroaches are usually terrestrial animals. | Water bugs are aquatic animals. |
Life Expectancy | 110 to 200 days | up to 365 days |
Body Shape | A roach has a round body shape, body and brownish color. | A water bug has a long, narrow, and round body. |
Diet | A cockroach’s diet may include plant materials, decaying organic matter, meats, starch, sugar, oil, tadpoles, snails and the like. | A water bug’s diet may include tadpoles, small fish, snails, insects, amphibians, and crustaceans. |
Antenna size | The size of a roach’s antenna is larger than that of a water bug. | The size of a water bug’s antenna is smaller than that of a roach. |
What is a Roach?
A roach, commonly called a cockroach, is an insect that belongs to the Blattodea classification. It has a round body shape, body and brownish colour.
Cockroaches don’t prefer hunting. Instead, they scavenge through the garbage. When it comes to temperament, cockroaches are shy.
Some food items of cockroaches include plant materials, decaying organic matter, meats, starch, sugar, oil, tadpoles, snails and the like.
Cockroaches are usually small in size. They put an individual at the risk of E.coli, salmonellosis, and listeriosis. Cockroaches are prey insects and usually come out in the dark.

What is a Water Bug?
A water bug is an insect that belongs to the classification Hemiptera. They are usually 2 to 4 inches in size, which is larger as compared to that of cockroaches.
The life expectancy of a water bug is 365 days. They are aquatic insects and usually reside in wet sewers, basements, slow-moving pools, freshwater ponds, and marshes.
Water bugs are predators. They hunt for their prey. After paralysing their prey with a proboscis, they inject a power liquifying enzyme which enables them to suck out the insides of the insect.
Water bugs usually fly around large lights and in parking lots. Bright light attracts these insects. A water bug’s bite can cause side effects that include vomiting, fever, cramping, breathing difficulties, and swelling.

Main Differences Between Roach and Water Bug
- A roach’s life span ranges from 110 to 200 days. In contrast, a water bug’s life span can go up to 365 days.
- A cockroach’s diet may include plant materials, decaying organic matter, meats, starch, sugar, oil, tadpoles, snails and the like. On the other hand, the diet of a water bug includes tadpoles, small fish, snails, insects, amphibians, and crustaceans.

References
- https://books.google.com/books?hl=en&lr=&id=R7eVRP08kasC&oi=fnd&pg=PP17&dq=cockroaches&ots=80ctfsJRpA&sig=fAN1ML90qDv8NSVyiOJBM2Wdsc0
- https://muse.jhu.edu/article/663671/summary
My name is Piyush Yadav, and I am a physicist passionate about making science more accessible to our readers. You can read more about me on my bio page.