Cockroaches: Fact or Fiction

Q: Are albino (white) cockroaches common in infested homes?

A: All newly molted cockroaches are white. Over the next several hours after ecdysis (molt), the wings and body gradually tan and acquire the characteristic color and pattern of the species. Although various mutants, including albino and white-eyed mutants, are occasionally found in lab colonies, they are extremely unlikely to be found outside the lab.

Q: Can female cockroaches reproduce without males?

A: Cockroaches, like many other animals (e.g., chicken), can oviposit unfertilized eggs, and, in most cockroaches, these eggs are inviable. In some cockroaches, however, unfertilized eggs can develop into females only, and parthenogenetic reproduction can be sustained for several generations. Some cockroaches are facultatively parthenogenetic (e.g., American cockroach), and one, Pycnoscelus surinamensis, appears to be an obligatory parthenogen; males are not known in this species.

Q: Do all cockroaches form egg cases?

A: Cockroach eggs are always packaged into oothecae. Some oothecae are thick and hard (American cockroach), some are thin and softer (German cockroach), and some have been reduced to a very thin membranous structure. In the family Blaberidae, a large clutch of eggs is contained within a very thin ootheca, extruded, rotated and withdrawn into the uterus for incubation. One species (Diploptera punctata) does not make an oothecal case at all.


Q: Can all cockroaches walk up walls and upside down on ceilings?

A: Cockroaches use a combination of pretarsal arolia that serve as suction cup-like devices, and tarsal pulvilli, which create friction with surfaces, for upward, downward and upside-down walking. These devices, together with the pretarsal claws, allow cockroaches to grip smooth and rough surfaces. But some cockroaches do not have arolia, severely limiting their ability to walk on smooth surfaces.

Q: Why do cockroaches die on their backs with their legs up?

A: Neurotoxic insecticides cause tremors and muscle spasms, flipping the cockroach on its back. A healthy cockroach can easily right itself, but without muscle coordination, the cockroach dies on its back. Cockroaches exposed to slow-acting insecticides that target respiration (energy production) also can die “face-down,” as they run out of energy without experiencing muscle spasms.

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