I found 60+ alive and approximately 20 dead on the floor of a large warehouse. The day before I hadn't seen any. As I took some of them outside to release them I noticed that after I opened my hand they immediately calmed down. Some propped themselves up on their front two legs opened their shells sideways aprox. 1mm at the aft end. They then emitted a low very quite buzzing sound which could be felt through my hand this kept on for about 5 minutes at which point I set them on the ground outside. If anyone can tell me more about this behavior please do. I have noticed what I think is swarming activity with water boatman also, and know that they too use sound to communicate with others of their species.