Cockroach or Water Bug? How to Tell the Difference in Montreal

Published April 7, 2026 · Extermination DMP

Someone finds a large brown insect in their bathroom or basement, takes a photo, and texts it to everyone they know with the caption: "IS THIS A COCKROACH?"

Half the time it is. Half the time it is not. And the difference matters — because the treatment, the urgency, and the cost are completely different.

The Three Bugs People Confuse

German Cockroach (the bad one)

Size: 12-15mm (about the size of a penny)
Color: Light brown to tan with two dark parallel stripes behind the head
Where you find them: Kitchen, bathroom, near appliances, in cupboards. Always indoors. They do not survive outside in Montreal.
Behavior: Fast runners. Active at night. If you turn on the kitchen light and see them scatter — that is German cockroaches.
Concern level: HIGH. German cockroaches reproduce rapidly and indicate an established indoor infestation. Professional treatment needed.

Oriental Cockroach (the "water bug")

Size: 25-30mm (about the size of a quarter)
Color: Dark brown to black, shiny
Where you find them: Basements, near drains, in crawl spaces, around water heaters. Sometimes outdoors near foundations.
Behavior: Slower than German cockroaches. Often found near water sources. Strong musty smell.
Concern level: MEDIUM. They indicate a moisture problem. Less rapid reproduction than German cockroaches, but still need professional treatment if recurring.

Ground Beetle (not a cockroach at all)

Size: 15-25mm
Color: Dark brown to black, hard shell
Where you find them: Basements, garages, near exterior doors. They wander in from outside.
Behavior: Slow. Does not run when the light turns on. Often found dead or dying.
Concern level: LOW. Ground beetles are outdoor insects that accidentally enter homes. They do not breed indoors and are not a sign of infestation. Pick it up and toss it outside.

How to Tell Them Apart

The Quick Test

Does it run fast when you turn on the light? → Probably a German cockroach. Is it near water and moving slowly? → Probably an Oriental cockroach (water bug). Is it already dead or barely moving? → Probably a ground beetle.

Body Shape

Cockroaches (both species) have flat, oval bodies that allow them to squeeze into cracks. Ground beetles have rounded, dome-shaped bodies with a hard shell. Pick it up (or poke it) — if the body feels crunchy and hard, it is likely a beetle. Cockroaches feel softer and flatter.

Antennae

Cockroaches have long, thin antennae — often as long as their body. Ground beetles have shorter, thicker antennae.

Wings

German cockroaches have wings but rarely fly. Oriental cockroaches have short wings and cannot fly. Ground beetles have wing covers but also rarely fly. Wings are not the best way to tell them apart, but if the bug flies — it is probably not a cockroach common to Montreal.

Why This Matters

If It Is a German Cockroach

You need professional treatment. German cockroaches do not go away on their own. A single egg case contains 30-40 nymphs, and a female produces 4-8 cases in her lifetime. Do the math — one cockroach becomes hundreds within months.

In an apartment building, you need coordinated treatment across multiple units. Solo treatment of your unit will fail.

Estimated cost: $150-$300 for initial treatment, $300-$600 for a full program with follow-ups.

If It Is an Oriental Cockroach

You need to fix the moisture problem and treat. Oriental cockroaches are associated with damp basements, leaking pipes, and poor drainage. Treating the bugs without fixing the moisture is temporary at best. Estimated cost: $150-$300 plus whatever the plumbing or waterproofing repair costs.

If It Is a Ground Beetle

You need to seal the entry point it used to get in. Check the gap under your basement door, window wells, and foundation cracks. No exterminator needed unless you are seeing them regularly (more than 2-3 per month), which suggests multiple entry points. Estimated cost: $0-$50 (caulk and a door sweep).

Frequently Asked Questions

Can cockroaches survive Montreal winters outdoors?

German cockroaches — no. They are strictly indoor insects and will die outdoors in Canadian winters. Oriental cockroaches can survive in protected outdoor areas (sewer systems, under debris) but are most active from May to October.

I found one cockroach. Is that an infestation?

For German cockroaches — probably yes. They are social insects that live in groups. If you see one, there are more in the walls. For Oriental cockroaches — one may be a stray from a floor drain or sewer access. But monitor closely and check for more over the following week.

Got a pest problem?

Extermination DMP serves Montreal, the South Shore, Laval & the West Island — 24/7.

Call 438-879-5706