Ivory Towers: Cockroaches by night

WE GO back to sleep for this week's scientific discovery, with a paper from the Journal of Sleep Research that could offer guidance to anyone troubled by cockroaches, or simply wondering what the gruesome little pests do during the day.

24-hr variation of vigilance in the cockroach Blaberus giganteus is the title of a paper by I Tobler and M Neuner-Jehle of the University of Zurich. 'Our objective,' they explain, 'was to investigate whether sleep-like states occur in the cockroach Blaberus giganteus by applying the methods formerly used for another cockroach species, Leucophaea maderae, and the scorpions, Heterometrus and Pandinus.'

The research fell into two parts: non-intrusive, during which they analysed the activity of cockroaches in motion and the body and antenna position of stationary ones, and intrusive, during which they vibrated or shook the cockroaches to keep them awake.

In the first part, they devised an activity scoring system by defining nine behavioural states of an alert cockroach and four sub-states of one at rest. Its behaviour was logged every minute (or 'one-minute real- time epoch' as the researchers more accurately describe it). The second stage involved shaking peaceful cockroaches to see if they woke up. ('Arousal threshold was measured by latency of behavioural response to a vibration stimulus.')

Several conclusions were drawn from all this. 'This study provides evidence for the existence of a 24-hr variation of vigilance in the cockroach. It further indicates that a 'rest deficit' gives rise to a compensatory response. The data support the notion that sleep-like states are present in these insects.'

But most of all they found that: 'The cockroaches showed a nocturnal behaviour exhibiting a bout of locomotion at dark onset which lasted several hours, and a preference for rest in the light period.' In other words, as anyone from Rentokil could have told them, cockroaches come out when it gets dark.

And if you don't want them to come out at night, shake them vigorously during the day, when their 'compensatory response to the rest deficit' will cut down their nocturnal perambulation.