Why a Daytime Sighting Matters

The default

They Are Built Not to Be Seen

Cockroaches are nocturnal and thigmotactic. They spend the light hours wedged into the tightest available gap, in contact on both sides, and they emerge in darkness to feed. Left to themselves that is what they do, without exception.

So the normal state of a cockroach infestation is invisible. People live above one for months and see nothing, which is why the first sighting so often comes when somebody goes into the kitchen at two in the morning and puts the light on.

Photographs on this page are for illustration purposes only.

The signal

Overflow, Not Curiosity

When cockroaches are seen in daylight or out in the open, the usual reason is competition. Harbourage space is finite, and as a population grows, individuals — often nymphs, which are lowest in the pecking order — are pushed out into places they would not otherwise choose.

Which is why a daytime sighting is read as a density signal rather than an event. It does not tell you exactly how many there are, but it tells you the population has outgrown its preferred space, and that takes time to happen.

The same logic applies to seeing them in a room away from the kitchen, or up on a worktop in the middle of the day.

The exceptions

Three Times It Means Something Else

Not every daytime sighting is density. Three other causes worth knowing:

• Something disturbed them. Building work, moving an appliance, lifting a floor or a drain being rodded will push them out immediately. If you saw one an hour after the plumber left, that is why.
• A repellent product was applied. Most consumer sprays repel, and a repelled population comes out and moves. This is one of the reasons spraying makes things look worse before it makes them look better, and then does not make them better.
• It arrived today. In a delivery, in cardboard, in a second-hand appliance. A single individual in an otherwise clean property with no droppings anywhere may genuinely be a new arrival.

Which is why the answer to "I saw one" is always "have a look for droppings", rather than a number.

What to do

Before You Clear It Up

Photograph it, next to something for scale. Species and size change the treatment, and a dead cockroach in a bin tells nobody anything.

Then check the four or five likely harbourages in that room with a torch — behind and under the fridge, under the sink, behind the kickboards, the backs of the drawers. What you are looking for is droppings, not more cockroaches.

Do not spray. If there is a population, a repellent scatters it into the structure and into neighbouring units, and that is a harder and more expensive problem than the one you started with.

Short answers

Cockroach Questions

Going further

Cockroach Guides