Cockroach Infestations in London Ontario: What You Need to Know

If you've seen a cockroach in your London Ontario home or apartment, act quickly. Cockroaches breed fast, spread through shared infrastructure, and become significantly harder to eliminate once a population is established. Here is what you are dealing with and how to approach it.

The Two Species You'll Encounter in London Ontario

German Cockroach (*Blattella germanica*)

This is the one you're most likely dealing with. German cockroaches are the dominant species in Ontario homes, apartments, and restaurants.

Key facts:

• Size: 12–15 mm. Tan to light brown. Two distinctive dark parallel stripes behind the head.
• Origin: They don't come from outside. They arrive through infested furniture, grocery boxes, second-hand appliances, or from an adjacent apartment through shared plumbing.
• Breeding rate: A single female produces an egg case (ootheca) containing 30–40 eggs every 3–4 weeks. One female can produce hundreds of offspring in a year.
• Behaviour: Strictly indoor pests. Prefer warm, humid environments close to food and water — under sinks, behind refrigerators, inside wall voids near plumbing, and inside appliance motor housings.

A daytime sighting almost always means the population is large enough that harborage space is crowded. If you're seeing German cockroaches in the day, the infestation is already significant.

American Cockroach (*Periplaneta americana*)

Larger (35–40 mm), reddish-brown, with a distinctive yellowish figure-eight pattern behind the head. In London Ontario, these typically enter through sewer connections, floor drains, and basement utility areas. They're less common in residential kitchens and more common in basements, laundry rooms, and commercial food-handling facilities.

Finding a single large American cockroach occasionally is a different situation than a German cockroach colony. However, finding multiple or finding them in kitchens warrants investigation.

Why London Homes Get Cockroaches

Older Housing Stock

London's older neighbourhoods — Old East Village, parts of Hamilton Road corridor, some of Argyle — have multi-unit buildings with aging plumbing that creates gaps in pipe chases and shared wall cavities. Cockroaches move freely between units through these pathways.

Grocery and Second-Hand Goods

German cockroaches are almost always introduced, not naturally invading. Egg cases or small nymphs hide in corrugated cardboard boxes, inside appliance motors, and in furniture upholstery. A single infested appliance brought in from a second-hand shop or a donation can start a colony.

Shared Infrastructure in Multi-Unit Buildings

This is the most significant driver of cockroach spread in London's apartment buildings. Plumbing chases, electrical conduits, and gaps around pipe penetrations between units allow cockroaches to move through buildings even when individual units are treated. Treating only the reported unit without addressing adjacent units is why cockroach problems recur.

How They Spread Through a Building

Cockroaches follow warmth, moisture, and food. Within a multi-unit building, this means:

1. Initial introduction in one unit (usually kitchen or bathroom)

2. Population grows until harborage is overcrowded

3. Cockroaches move through pipe chases to adjacent units on the same floor

4. Over weeks, they spread vertically through the same plumbing stack

5. By the time a second tenant reports activity, the infestation spans multiple units

What Treatment Actually Looks Like

What doesn't work:

• Foggers ("bug bombs"): Scatter cockroaches into wall voids without killing the population. They also contribute to insecticide resistance and contaminate surfaces. Do not use them.
• Residual spray barriers: Applied without reaching harborage areas, these kill surface-level cockroaches but not the colony.
• Treating one unit in a multi-unit building: Guarantees re-infestation within weeks.

What works:

1. Gel bait in harborage zones: Applied in cracks, behind appliances, under sinks, inside cabinet hinges. Cockroaches consume the bait and carry it back to the harborage, killing colony members they never directly contact.

2. Insect growth regulators (IGRs): Break the breeding cycle by preventing nymphs from reaching reproductive maturity. Essential for eliminating an established population.

3. Adjacent unit treatment: In apartments, treating the reported unit plus adjacent units (above, below, beside) is standard practice.

4. Follow-up monitoring: Bait stations with monitoring capability confirm whether population is declining and where activity persists.

For landlords and property managers with cockroach activity in their building, a documented treatment program is also relevant to your obligations under the Residential Tenancies Act.

Book a cockroach inspection or learn more about cockroach control for your home or building.