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After Sydney's spring rain: millipedes and centipedes moving indoors
When a spring downpour soaks the garden overnight and the sun comes up hot the next morning, the first indoor sightings often come from the same place: the laundry, the garage, the back door or a ground-floor bathroom. Here is a calm way to work out what you are dealing with and what to do next.
Sydney's spring weather this week is a textbook trigger. Overnight rain soaked garden beds, lawn edges and mulch, and by Saturday morning the temperature was climbing quickly under a clear sky. That combination — wet soil followed by warm, drying conditions — pushes soil-dwelling creatures upward and toward the edges of buildings. Millipedes and centipedes are among the first to show up on door thresholds, in garage corners and along ground-floor skirting boards. They are not feeding on your home, but their arrival tells you something about how moisture and entry points are lining up at the moment.
Why spring rain and heat bring them inside
Millipedes and centipedes live in damp soil, leaf litter, mulch and under rocks. They breathe through their skin, which means they dry out quickly. Heavy rain can push them out of saturated ground. Then, as the sun comes out and the surface begins to dry, they head for the dark, damp places they are adapted to — and the edge of a house, a weep hole, a door gap or a subfloor ventilation grille offers exactly that.
This is why the sightings usually cluster in the day or two after rain, especially when the weather swings from wet to warm. In Sydney's spring, that swing happens regularly: a cold overnight shower followed by a 25 to 30 degree afternoon is enough to start the movement.
Neither millipedes nor centipedes damage structural timber, infest food, or reproduce indoors in large numbers. Most die quickly inside a dry house. They are a seasonal symptom of damp garden edges and entry points, not an established indoor infestation.
Millipede or centipede? A quick way to tell
People often mix the two up, and the difference matters for how concerned you should be. Millipedes are slow, cylindrical, dark-coloured creatures with many tiny legs, two pairs per body segment. They curl into a tight spiral when disturbed. They feed on decaying plant matter and do not bite.
Centipedes are flatter, faster and usually paler brown or yellowish, with one pair of longer legs per segment and prominent antennae. The common house centipede runs quickly across floors and walls. It can bite if handled roughly, though the sting is generally mild and comparable to a bee sting. It is a predator, feeding on other small insects rather than on your home.
- Slow, curly, many short legs, dark body — likely a millipede.
- Fast, flat, long legs and antennae — likely a centipede.
- Found in large numbers on a driveway or path after rain — millipedes on a mass migration.
- Seen singly, darting across a bathroom or laundry floor — usually a centipede hunting for other insects.
Where they are most likely to show up
In Sydney homes, post-rain sightings cluster around ground-floor rooms that share a wall with a garden bed, lawn or retaining wall. Laundries, garages, bathrooms and walk-in robes at the wet end of the house are common spots. You may also find them around external doors, in shed corners, or in a subfloor space if access points are open.
Check door thresholds and weather seals at the back of the house.
Look along skirting boards in laundries and ground-floor bathrooms.
Inspect garage corners and beneath storage shelving.
Check weep holes and subfloor ventilation grilles for obvious gaps or blocked mesh.
Reduce repeat sightings without over-treating
The most effective first step is not a spray. It is reducing the damp garden-edge conditions that are pushing them toward the building. Pull mulch and leaf litter back from the foundation edge so soil is not piled against the wall. Clear leaves from door tracks, weep hole covers and ventilation grilles. Check that downpipes and drains are clear so water does not pool next to the slab.
Inside, sweep or vacuum any you find and dispose of the vacuum bag promptly. Seal obvious gaps under external doors where weather seals are worn. If you use a commercially labelled perimeter spray, apply it only as directed and only around the external threshold — do not rely on repeated indoor spraying to solve a movement problem that is really coming from the garden.
If you are in a strata or rental property, photograph the garden beds, drains and any obvious structural gaps before making material changes. That record helps the property manager or strata committee understand whether drainage or ground-level works are contributing.
When it is worth asking for help
A handful of millipedes or a single centipede after rain is normal and usually settles within a few days as the ground dries. The situations that warrant a closer look are when sightings continue well beyond the post-rain window, when you are finding them in large numbers inside living areas, or when the same damp ground-level conditions keep recreating the problem week after week.
- Sightings continue two weeks after the rain, well beyond the normal movement window.
- You are finding them in multiple rooms or on upper floors, which suggests a different entry route than a ground-floor crawl.
- Garden beds, retaining walls or drains are saturated and directly abut the building.
- You are unsure what insect you are seeing, or bites are occurring in a bedroom or bedding area.
A brief inspection can tell you whether you are looking at a normal post-rain movement or a persistent entry-point and moisture issue that needs a different fix.
SEEING THEM INSIDE AFTER THE RAIN?
Text a photo and the room where you are finding them.
Include your suburb and whether sightings are continuing after the rain.