From November to March, our call-out pattern changes completely: cockroaches appearing from floor drains after the first floods, ant columns marching out of saturated gardens into kitchens, rats moving off flooded ground into roof voids. None of this is bad luck — it is physics. Rain fills the drainage network, saturates the soil and floods the burrows, and every displaced pest heads for the nearest dry, warm building. The villas that stay quiet through the wet months are the ones that closed their entry points in October, before the pressure arrived. Here is the exact pre-season routine, in the order we do it.
What the First Rains Actually Do
Three movements happen in the first fortnight of serious rain, and each one targets a different part of the villa. Cockroaches come up: Bali's drains are a cockroach highway all year, but when storm water fills them, the roaches exit through every floor drain, overflow and gully that is not sealed or treated. Ants come in: ground-nesting species abandon waterlogged nests and relocate — often straight into wall cavities and kitchen voids, which is why wet-season ant invasions appear overnight and in force. Rats come up and in: flooded burrows and drains push rodents to higher, drier ground — compost corners, store rooms, ceiling spaces. We explain the full annual cycle in our guide to pest seasonality in Bali; the short version is that the wet season is the one period when all three pressures peak at once.
The October Pest-Proofing Checklist
Clear and treat every drain
Flush floor drains, gullies and yard channels so storm water runs instead of backing up, then have the drain network treated with gel and residual product — this is the core of our cockroach control work and the single highest-impact pre-season job.
Fit or check drain covers and traps
Every floor drain should have a sealed cover or water trap. A dry U-trap is an open door; pour water into rarely used drains weekly so the seal holds.
Seal the pest-sized gaps
Walk the building at dusk with a torch: gaps under external doors, unscreened vents, AC pipe penetrations, broken fly screens. A rat needs 2 cm, a cockroach needs 3 mm. Door brushes, mesh and sealant close most of them in an afternoon.
Close the rodent routes
Cut back branches touching the roof, check roof-void access points, and get bins and compost into sealed containers. If you heard scratching in the ceiling last wet season, book rodent control now — bait and proofing work best before the migration, not during it.
Strip the standing-water nurseries
Plant saucers, blocked gutters, tarps and unused containers become breeding and drinking sites the first week of rain. Empty, invert or remove them — it cuts mosquito and roach pressure around the building at zero cost.
Book a pre-season barrier treatment
A general pest treatment in October — residual perimeter spray, drain gel and baits — intercepts the migration instead of chasing it. Costs are published on our treatment costs page.
Early Warnings: What You See vs What It Means
| What you notice in week one of rain | What it usually means | How urgent |
|---|---|---|
| Cockroaches around floor drains at night | Drain network flooding; untreated drains | Treat drains now — numbers compound weekly |
| Sudden ant trails indoors | Displaced colony relocating into the building | Days — gel baiting works best on fresh trails |
| Scratching in the ceiling at dusk | Rats moved off flooded ground into the roof void | High — nesting and wiring damage follow fast |
| Winged insects swarming lights after rain | Termite or ant swarm from a nearby colony | Photograph and send to us for a free ID |
The common thread: everything on this list is cheap to deal with in the first week and expensive after a month. Send a photo the day you notice it, not after the long weekend.
Why Prevention Beats the Wet-Season Call-Out
A reactive call-out in January treats a population that has already established indoors — and in wet season, reinfestation pressure from outside is constant, so one-off visits fade faster than at any other time of year. A pre-season barrier plus sealed entry points means the rain-driven migration mostly breaks against the outside of your villa. That is why our wet-season recommendation is simple: do the checklist above in October, take one combined treatment before the rains settle in, and switch to a scheduled program if your area floods every year. Villas on monthly programs in flood-prone streets of Canggu and Seminyak are the ones whose owners we do not hear from in January — which is the point.
Get Pest-Proofed Before the Rains
October bookings get done before the migration starts. Send photos of your drains and kitchen — fixed quote the same day.
WhatsApp a Pre-Season Quote