Cockroaches on Oahu: How to Keep Them Out This Wet Season (2026)

You flip on the kitchen light at 10 p.m. and something big and brown bolts under the stove. Or worse, it flies. If you grew up here, you already know the B-52, and you know October is when they start showing up in places they have no business being.

Oahu’s wet season runs from October through April, and every year it brings a predictable wave of cockroach calls from Waipahu to Kailua. This fall has a twist, though. Forecasters are calling for a strong El Niño, which usually means a drier winter for Hawaii. That sounds like good news. For cockroaches, it isn’t, and the reason comes down to water.

Here’s what Oahu homeowners need to know heading into the season.

Know Which Roach You’re Dealing With

According to University of Hawaii CTAHR research, Hawaii is home to 19 species of cockroaches, and eight of them have been found inside Oahu homes. You don’t need to know all eight. You do need to know the difference between the two that cause most of the trouble, because they get in differently and they’re controlled differently.

• American cockroach (the “B-52”). Big, reddish-brown, up to two inches long, and yes, it flies. This one lives outside your house in sewer lines, storm drains, cesspools, green waste piles, and the leaf bases of palms. It comes inside at night through floor drains, weep holes, gaps under doors, and plumbing penetrations.
• German cockroach. Small, tan, with two dark stripes behind the head. This one breeds indoors, in kitchens and bathrooms, behind the fridge, inside cabinet hinges and appliance motors. If you’re seeing small roaches during the day, that usually means the population is already large.
• Brown-banded cockroach. Less common, but it likes the drier, warmer spots up high: inside electronics, ceilings, and picture frames.

The distinction matters. Spraying the kitchen won’t stop B-52s coming up from the sewer, and sealing the doors won’t touch a German cockroach colony that’s already living in your dishwasher.

Wet Season, El Niño, and Why Roaches Come Inside

Last winter was the wettest wet season Hawaii has seen in roughly 30 years. Heavy rain floods outdoor harborage like drains, rock walls, mulch beds, and ground cover, and it pushes American cockroaches toward higher, drier ground. On Oahu, that usually means your garage, your lanai, and your kitchen.

This year the pattern looks different. NOAA’s Climate Prediction Center gives a greater than 90% chance of a very strong El Niño this fall and winter. NOAA’s historical records show roughly a 70% chance of drought during a wet season that follows an El Niño onset, with rainfall running a few inches below normal.

A drier winter doesn’t mean fewer roaches. It means they move for a different reason. Cockroaches can go a month without food but only about a week without water. When the yard dries out, they go looking for moisture, and the most reliable water on any property is inside the house:

• Under kitchen and bathroom sinks, especially with a slow drip
• AC condensate lines and drip pans
• Water heater closets
• Floor drains and shower drains that don’t get used often
• Pet water bowls left out overnight

We’ll still get Kona lows and heavy rain events between dry spells, and each one sends another wave inside. Either way, October is when roach pressure goes up in Honolulu, Pearl City, Aiea, Kapolei, and Ewa Beach. The only thing that changes is what pushes them in.

It’s a Health Issue, Not Just a Gross-Out

Cockroaches are more than an unpleasant surprise in the dark. Their droppings, shed skins, and saliva carry allergens that are a well-documented asthma trigger, especially for keiki. A national survey by the National Institute of Environmental Health Sciences and HUD found cockroach allergen in an estimated 63% of U.S. homes, and the National Pest Management Association reports that figure climbs to 78% to 98% of homes in urban areas.

Oahu’s year-round warmth makes that worse. On the mainland, winter knocks cockroach activity back for a few months. Here, there’s no off-season. Roaches breed continuously, and the allergens build up in kitchens, cabinets, and carpet all year long.

American cockroaches that travel between sewer lines and your countertop can also carry bacteria onto food prep surfaces. That’s reason enough to treat a few nighttime sightings as a signal and not just bad luck.

What Works: A Practical Plan for Oahu Homes

Most of the cockroach control that lasts comes from exclusion and moisture control. Products matter, but they’re only part of the job. Here’s what we recommend to homeowners from Mililani to Hawaii Kai:

1. Seal the way in. Install door sweeps on exterior doors and the garage door. Close gaps around plumbing under sinks with caulk or escutcheon plates. Make sure weep holes and vents have intact screening.
2. Close up your drains. Run water into rarely used floor drains and shower drains weekly so the trap stays full. Cover drains in garages and laundry rooms at night if B-52s keep coming up through them.
3. Fix the drips. A leaky P-trap or a sweating AC line is a water source for an entire colony. Check under every sink this month.
4. Clean up outside. Move green waste, stacked lumber, and mulch at least a couple of feet back from the foundation. Trim palm fronds and dense hedges away from the walls. Keep trash bins sealed and away from doors.
5. Don’t feed them. Wipe down counters at night, store food in sealed containers, and pick up pet food bowls after dinner.

On the professional side, the tools have improved. In 2026 the industry got its first new mode of action for cockroach control in about two decades: a new gel bait with EPA Reduced-Risk status. Modern baits like this go into cracks, crevices, and hinges where cockroaches hide, not out in the open where pets and keiki can reach them. Combined with a targeted exterior perimeter treatment for American cockroaches, this gets results without fogging your whole house.

For German cockroaches, DIY sprays often make things worse. Many repellent sprays scatter the colony deeper into walls and appliances. If you’re seeing small roaches in daylight, that’s the time to bring in a professional.

Get Ahead of Roach Season

We’re Kaulana Pest Control, locally owned and operated, and we treat homes and businesses across Oahu, including Honolulu, Waipahu, Pearl City, Aiea, Mililani, Kapolei, Ewa Beach, Kaneohe, Kailua, and Hawaii Kai. We know which neighborhoods run heavy on B-52s from the storm drains, which older homes have the plumbing gaps they slip through, and how to treat without putting your ohana or pets at risk.

If you’ve started seeing roaches at night, don’t wait for them to settle in for the winter. Request a free inspection and quote and we’ll find where they’re getting in, tell you which species you’re dealing with, and give you a clear plan to stop them.

Malama your home, and it’ll take care of your ohana.