Coastal Brown Ants in Melbourne
How to recognise the big-headed ant, why it heaps soil between your pavers, and how our team clears a colony that spraying only scatters.
Written by Muzi Tsolakis, Founder and Competency Assessor, Pest Management Victoria. Last reviewed 18 July 2026.
The coastal brown ant, Pheidole megacephala, is the light-brown ant Melbourne households notice by the fine piles of soil it heaps up between pavers and along path edges. It is also called the big-headed ant, after the oversized soldiers that give the colony away, and it is one of the world's more successful invasive ants. Around a home it is both a nuisance and a quiet problem for paving and native wildlife. This guide explains how to recognise the coastal brown ant, why the soil heaps and the trails appear, and how our technicians clear a colony that a surface spray only splits and scatters.
How to identify a coastal brown ant
The coastal brown ant is small and light yellow-brown to reddish-brown, and its most reliable feature is that it comes in two sizes. Species of Pheidole are dimorphic, with two kinds of worker: the small minor workers, around one and a half to two millimetres long with a normal-shaped head, and the major workers, whose head is enormous in proportion to the body and carries heavy mandibles, as the Museums Victoria record for the big-headed ants describes. Those large-headed soldiers are what earn the species the name big-headed ant, and spotting a few among a trail of smaller workers is the quickest confirmation.
The minor workers do most of the foraging while the big-headed majors use their mandibles to crush seeds and defend the nest. As with all ants, the coastal brown ant does no damage to timber; that is the work of termites, a different insect entirely. The concern with this species is its numbers, its habit of moving soil, and the way it pushes other ants out.
Where they nest and why they spread
Coastal brown ants nest in the soil: under pavers and slabs, along foundation edges, beneath pot plants and through garden beds. The tell-tale sign around a Melbourne home is the loose, fine soil they excavate and heap up between pavers, along the mortar lines of brick paving and at the edges of paths and driveways, a little more appearing after every warm spell.
This is a highly successful invasive ant, and it is regarded as a danger to native ants, which it displaces as it spreads through a garden. A single infestation is usually made up of many linked nests rather than one, and the colony readily buds off new nests when it is disturbed. It forages for sweet and protein foods and tends sap-sucking insects such as aphids and scale for their honeydew, which can make those garden pests worse at the same time. The combination of many nests, soil-moving and easy budding is what makes the coastal brown ant harder to clear than a single-nest species.
Why they are a problem around the home
The coastal brown ant brings three practical problems. The first is the soil it deposits: over a season the fine spoil heaped between pavers and along path edges loosens the bedding sand, so paving can settle and lift unevenly and mortar lines wash out. The second is the indoor nuisance, as foragers trail inside for food and water and contaminate benches and stored goods, the same hygiene concern as any household ant. The third is in the garden, where the colony protects aphids and scale for their honeydew and displaces the native ants that would otherwise keep the balance.
None of this threatens the structure of the house, since ants do not eat timber, but a large, spreading coastal brown ant population is a persistent problem that rarely resolves on its own and tends to grow across a property year on year if it is left.
Why spraying scatters the colony
A surface spray is the wrong tool for this ant and usually makes the situation worse. Because a coastal brown ant infestation is many linked nests rather than one, a repellent spray kills a few visible foragers, wipes the trail for a day, and prompts the disturbed nests to bud and split into still more nests spread further across the garden. The queens, sitting safely underground, are never touched.
Clearing coastal brown ants dependably means reaching the queens in those nests, and the reliable way to do that is a baiting program matched to the species. A bait the foragers carry down and share through the linked nests reaches the queens and brood, which is what actually reduces the population, and it is placed on the active trails and nest sites rather than sprayed across them. Getting the bait type and placement right for this particular ant is the part that separates a lasting result from a brief knockdown.
How Protech treats coastal brown ants
Every treatment begins with an inspection to confirm the species by its big-headed soldiers, map the trails and soil heaps, and locate the network of nests around the paving, foundations and garden. From there we run a baiting program matched to what the colony is feeding on, placed on the active runs and nest sites so the foragers carry it down and share it through the linked nests to reach the queens. Because the population is spread across many nests, we plan for the colony to reduce over a few weeks rather than overnight, and a follow-up check confirms the nests are clearing and lets us top up bait where needed.
We also point out the paving, moisture and garden conditions worth addressing so a new population does not simply re-establish, and we explain the work as we go. Our ant work covers ant control for homes and commercial premises across Melbourne, and every general treatment is backed by our pest-free guarantee: if the ants return within the guarantee period, so do we, at no extra charge. If you are seeing fine soil heaped between the pavers and trails of light-brown ants that keep coming back, an inspection maps the nests behind it. Call our Melbourne team on 03 9449 4244 or request a free quote, and you can read our other species guides in the pest library.
Coastal Brown Ants in Melbourne FAQs
What is the ant heaping soil between my pavers?
In Melbourne that is very often the coastal brown ant (Pheidole megacephala), also called the big-headed ant. It nests in the soil under paving and heaps fine excavated spoil up between the pavers and along path edges. A quick way to confirm it is to look for the oversized big-headed soldiers among the smaller workers in a trail.
Why is it called the big-headed ant?
Because the colony has two sizes of worker. The small minor workers do most of the foraging, while the major workers have a head that is enormous in proportion to their body, with heavy mandibles they use to crush seeds and defend the nest. Seeing a few of those big-headed soldiers among a trail of smaller ants is the clearest way to identify the species.
Do coastal brown ants damage paving or the house?
They do not damage the house structure, because ants do not eat timber. They do affect paving: the fine soil they excavate and heap between pavers loosens the bedding sand over a season, so paving can settle and lift unevenly and mortar lines wash out. They are also a garden problem, protecting aphids and scale and displacing native ants.
Why does spraying make coastal brown ants worse?
Because an infestation is many linked nests, not one. A repellent spray kills a few foragers and prompts the disturbed nests to bud and split into more nests spread further across the garden, while the underground queens are never touched. Baiting that the ants carry down to the queens is what actually reduces the population.
How long does it take to clear coastal brown ants?
Because the population is spread across many nests, a baiting program usually reduces it over a few weeks rather than overnight, and a follow-up check confirms the nests are clearing. That is slower than a spray's brief knockdown, but it reaches the queens and gives a lasting result rather than scattering the colony.
Do you guarantee ant treatments?
Yes. Our general pest treatments, including coastal brown ant work, are backed by a pest-free guarantee. If the ants return within the guarantee period we come back and re-treat at no extra charge. We confirm the length of the guarantee period in writing with your quote.
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