[3] With the destruction of its typical habitat and its poor dispersal abilities, it has been listed as being an endangered species in Japan.

As development has reduced these types of habitat, it has taken to living in rice paddies and agricultural water stores.

[5] The male Appasus japonicus initiates courtship in this species by performing a series of up-and-down movements, a "pumping display".

The male carries the eggs and tends them until they hatch; this takes a month or so in the spring but about a week in the warmer waters of summer.

The proboscis is used to stab the prey and then inject it with a toxic saliva, after which the bug sucks out the liquefied contents.