Most people think cockroaches are a summer problem. In Toowoomba, German cockroaches actually peak in winter. Here's why — and how to break the cycle.
The species changes when the temperature drops
Across most of Queensland the big outdoor roaches you see scuttling at night are American or Australian cockroaches. They love warm wet conditions and they're mostly a summer headache.
German cockroaches (Blattella germanica) are different. They're small, light tan, with two dark stripes behind the head, and they live exclusively indoors. They never go outside — which is exactly why a Toowoomba winter is their best season.
Why winter helps them, not us
Toowoomba sits at 700m elevation and gets genuinely cold nights from May to August. Every warm-blooded thing in your kitchen — the back of the fridge, the dishwasher motor, under the toaster, the cavity behind the oven — becomes a tropical microclimate.
German cockroaches breed fastest at 25–33°C. A single female produces 30–40 nymphs every few weeks, and they reach adulthood in about 60 days. In a warm cavity with crumbs and a leaking pipe, a small population becomes a major infestation in a single season.
Where they hide in a Toowoomba kitchen
Behind and underneath the dishwasher (the motor stays warm and there's always moisture).
Inside the cavity at the back of the oven and rangehood.
Inside the hinges of cupboard doors, particularly under the sink.
Inside small appliances — kettles, toasters, coffee machines.
Behind tiled splashbacks where the grout has cracked.
Why surface sprays don't work
Supermarket fly-spray and surface bombs scatter the population. The roaches you can see die — the 80% you can't see push deeper into wall cavities and lay another batch of eggs.
Modern gel baits work in the opposite way. A pea-sized drop placed in the right harborage is eaten by foraging roaches, who carry the active back to the harborage and feed it to the nymphs. One properly placed program collapses the entire colony in 7–14 days.
How to keep them out next winter
Clean behind the appliances — properly, twice a year. Pull the fridge out, vacuum the floor and the coils.
Fix the slow leaks. A German cockroach needs water more than food; a damp under-sink cabinet keeps them going for weeks.
Seal the cracks. Caulk around the splashback, around pipe penetrations and where the kickboard meets the floor.
Be careful with second-hand whitegoods. The single most common way a Toowoomba home picks up German cockroaches is a fridge, microwave or dishwasher from a marketplace listing.