The Smell, and What It Means

What it is

Aggregation Pheromone, Mostly

Cockroaches produce aggregation pheromones — chemical signals that tell other cockroaches this is a good place to be. They are deposited in the droppings, which is why harbourages build up a concentration of it over time and why cockroaches return to the same gaps rather than wandering.

That, together with the secretions and the accumulated droppings themselves, is what produces the smell. Descriptions vary: musty, oily, greasy, slightly sweet, like damp cardboard, occasionally like stale almonds. Nobody describes it as pleasant.

What it tells you

It Is About Numbers

This is the part worth holding onto. You do not smell a small cockroach problem. The odour is a function of accumulated droppings and secretions in confined spaces, which takes both time and population.

So noticing it is not a signal that something has just started. It is a signal that there is a substantial, established population somewhere fairly close to where you are standing — usually inside a unit or behind an appliance in that room.

In a food business it is also the signal that a customer might notice, which puts it on a different footing entirely.

Where you notice it

Confined, Warm and Unventilated

It is strongest where air does not move: inside a closed cupboard, particularly under the sink; in the gap behind a fridge when you pull it out; in a cellar; in a cupboard housing a boiler; in a store room; in the void behind kickboards.

People frequently report noticing it on opening a cupboard that has been shut for a while, or on returning to a property after being away, and then not noticing it again. That is your nose adapting rather than the smell going.

If you want to test it, shut the room up for a few hours and come back in from outside.

What it is not

Two Things It Gets Confused With

Damp and mould produce a musty smell too, and so does a dead rodent, though that is unmistakably different once you have met it.

The distinguishing factor is location and company. A cockroach smell is concentrated at a harbourage rather than general to a room, and it arrives with other evidence — droppings, smearing, shed skins. A general musty smell through a whole room with no droppings anywhere is more likely to be damp.

If you are not sure, that is a reasonable thing to ring about. Establishing there is nothing there is a useful outcome too.

Short answers

Cockroach Questions

Going further

Cockroach Guides