Gelastocoridae most likely Nerthra sp.  This is a tiny bug. Notice the sand grains.    William Archer  Esperance, WA, Australia tells us in his blog: "Toad Bugs are small (between 0.5 - 1 cm or around 1/4" in length) and mostly live near aquatic habitats, but some can live in much drier environments. They belong to the worldwide Gelastocoridae family, which has over 100 species in three genera, but in Australia there is one subfamily (Nerthrinae) with only one genus (Nerthra) containing 21 species. I do not know if I have photographed (above [photo in his blog]) one of more species (I suspect two), but the five in the SW of WA are Nerthra adspersa, N. femoralis, N. hirsuta, N. stali and N. tuberculata, should anyone be interested in following them up.  Despite their small size these bugs are ferocious predators, by ambushing, running down, then pouncing on their invertebrate prey. They grasp their captives in their modified claw-like front legs and then immediately begin to siphon their soft inner tissues. I have seen them hunting ants in this manner (photo center right above), where the bug has been surprisingly fast and agile, with capture happening only a second or two from when the ant was first spotted."