Species: Pycnoscelus striatus (Insecta: Blattodea)
Known Range: Malaysia, Sumatra, the Philippines
Size: (Adult) 15 mm long , ~diameter of 10-sen coin
Interviewed: Dr Lim Teck Wyn, biologist
(Photo: Shaharin Yussof )
“CUTE” IS how Teck Wyn describes the cave cockroach, Pycnoscelus striatus. “The nymphs”—the juvenile stage of cockroaches—“are adorable, scurrying sort of things.”
These aren’t the cockroaches that hide in your drains or behind your toilet. Those six-legged members of many Malaysian households are the American cockroach, Periplaneta americana.
While the American cockroach would be happy to share your food, cave cockroaches like Pycnoscelus striatus can’t survive in your house; they need to burrow into guano—bat faeces—and eat it.
Teck Wyn describes them here:
The cave cockroach isn’t a pest, says Teck Wyn. In fact, there are over 4,000 cockroach species, and only a handful intrude into the comfort of our homes.
And cockroaches deserve special praise for their role in caves. Cockroaches keep cave ecosystems running. They munch and grow on guano, and are in turn eaten by predators like spiders and scorpions.
A cockroach meal transfers the nutrients in guano to the rest of the cave residents. Cockroaches also eat dead animals.
A cave would be different without cave cockroaches, says Teck Wyn.
In Malaysia, Pycnoscelus striatus is most studied in the Dark Cave of Batu Caves, Selangor. They once crowded the caves. But after a walkway was built for tourists to explore the Dark Cave in the 1970s, Pycnoscelus striatus numbers there plummeted, says Teck Wyn.
Meanwhile, the American cockroach invaded the Dark Cave in huge numbers. In the 1980s, American cockroaches in the Dark Cave were “so many that you would be repulsed by them”, says Teck Wyn.
Some concerned cave experts even suggested that American cockroaches would eventually displace the native cave cockroach.
Luckily, the American cockroach’s speculated takeover fizzled. Their numbers retreated after Dark Cave caretakers removed the walkway’s lighting and awning in 1989 and 2012, respectively.
The American cockroach are far fewer in number now and confined mostly to the lit areas and near the walkway.
The good news is that Teck Wyn’s early 2019 survey found a healthy population of Pycnoscelus striatus living inside guano throughout the Dark Cave. Teck Wyn says the cave roach also thrived in thick guano in another secluded cave at the top of the hill.
What’s more, he found that the cave cockroach and others like the American cockroach and Australian cockroach like different parts of a cave.
So how does one survey cockroaches? Teck Wyn’s survey technique was quick and absolute—he walked into the guano and, at specific intervals, scooped up some in his hands and looked for cockroaches.
We understand if you are not too keenabout counting cockroaches in your palms. Still, don’t let your disgust of pest cockroaches stop you from appreciating the many beautiful—and important—cockroaches out in the wild.
K.H. Tan. 1970. Reproduction of the cave-roach Pycnosceles striatus. Malayan Nature Journal 23: 168–170.
H.E. McClure et al. 1967. Fauna of the Dark Cave, Batu Caves, Kuala Lumpur, Malaysia. Pacific Insects 9: 399-428.