Again, it depends on the species. In general, gonodactylids are diurnal, squillids are nocturnal and lysiosquillids vary. Most Gonodactylids are strictly diurnal, opening at dawn and closing their cavities before sunset. The same is true of Pseudosquilla and Odontodactylus brevirostris and O. havanensis. O. sycllarus - the peacock - is a puzzle. I frequently watch them with night vision devices and during parts of the lunar cycle they are active at night - usually during a full moon. However, most activity generally occurs during the day.
Hemisquilla ensigera is day active except that it closes for four hours around noon.
Echinosquilla is crepuscular. We only see it at dawn and dusk.
I should stress, however, that there are at least 600+ species of stomatopod and we have studied the behavior of fewer than 100. If you want a good idea of activity, keep the animal in a tank near a window, turn out the lights, and watch it for a few days. Usually they will assume typical field activity in a week or so.
Roy
