Cockroaches have a bad reputation. People think of them as dirty creatures that live in filthy environments. This is far from the truth. Cockroaches are quite fastidious - especially with regards to their antennae.
The antennae receive regular cleaning. The cockroach grabs an antenna with a front leg and runs it through its mouth. Researchers have known for a very long time that cockroaches and many other insects clean themselves, but now they also know why. When American cockroaches (Periplaneta americana) were prevented from cleaning their antennae—by gluing their mouth parts together for 24 hours—a shiny, wax-like layer was discovered on the antennae. This layer plugs up the miniscule openings to odour-sensing cells. By measuring the electrical activity in these cells, it became clear that the waxy layer disrupted the perception of food and other odours. This layer is produced continuously; it is probably necessary for the prevention of dehydration. By cleaning the antennae, excess wax is removed and, with it, also dust and other dirt that has clung to it.
Other insects experimentally prevented from keeping themselves clean (houseflies, German cockroaches, and certain kinds of ants) were also plagued with wax accumulation.