Reading Droppings and Smear Marks

Droppings

Coffee Grounds, Pepper and Ink

What cockroach droppings look like depends on the size of the insect producing them.

German cockroach droppings are tiny — like coarsely ground black pepper or coffee grounds. Scattered in the places they harbour: the back of a cupboard, along the top edge of a unit, inside the fridge motor housing, in the runners of a drawer.

Oriental and American droppings are bigger and more cylindrical, with blunt ends and visible ridges running along them. Roughly the size of a grain of rice for an American.

The useful distinction from mouse droppings, which people confuse them with constantly: mouse droppings are smooth-sided and tapered to a point at each end. Cockroach droppings of that size have blunt ends and longitudinal ridges. If you can see ridges, it is not a mouse.

Smearing

What It Means and Where It Is

Where there is a lot of moisture, droppings do not stay dry and discrete. They become dark irregular smears and streaks, usually on vertical surfaces, along the edges the insects run, and around harbourage entrances.

That is worth noticing for two reasons. It means the population is large enough and settled enough to produce it, and it means there is water nearby — which is usually the thing keeping the infestation going.

Smearing behind a dishwasher or under a sink alongside a slow leak is one of the commonest findings there is, and fixing the leak does more than most of what else you could do.

Egg cases

The One That Tells You It Is Established

An ootheca is a hard purse-shaped capsule, roughly 8mm for a German and rather larger and darker for the others, with visible ridging along one edge. They are found in the harbourage itself and often stuck to a surface.

Finding empty ones matters more than finding full ones. An empty ootheca, split along its seam, means a generation has already hatched in your building. That moves the problem from "something came in" to "something is breeding", which is a different job.

Leave them where they are and photograph them. They are the best single piece of evidence a technician can be shown.

What else

Shed Skins and the Places to Look

Cockroaches moult repeatedly as they grow, and the shed skins are pale, papery and hollow — recognisably cockroach-shaped but translucent. They collect in harbourages.

The places worth checking, in order of how often they produce something:

• Behind and underneath the fridge, especially the motor compartment
• Under and behind the dishwasher and the washing machine
• The cupboard under the sink, particularly the back corners
• The gap between units, and behind the kickboards
• Inside the runners and the backs of drawers
• Around the boiler and any warm pipework
• Behind a wall-mounted microwave or extractor

A torch and a phone camera held into a gap will show you more than kneeling and squinting.

Short answers

Cockroach Questions

Going further

Cockroach Guides