Record of the first expedition to HD 85512 b, candidate for human colonisation.
The helmet camera of the recording team member shows the explorers walking across a plain overgrown by mosslike plants. To the left of the team are boulders, more than manhigh, strewn across the plain, possibly remnants of glacial activity. The camera and the rest of the explorers turn when a flock of sixlegged creatures, resembling miniature tapirs with stubby wings, amble past, taking no notice of the humans.
There is some rustling and a muffled sound, like someone getting bodychecked and the camera turns back. One of the team is missing, Dr. Geoffrey Simmons, exobiologist, simply gone in the three seconds the camera was aimed away. The explorers turn, call out Dr Simmons name and start to spread out, more confused than afraid, some obviously thinking the doctor is playing a prank. It seems he was something of a practical joker.
If you care to zoom in between the boulders, you'll see movement in the leaf litter. That's where it was hidden. It took two more of our people before anyone had realised what was happening.
photo by Coastlander
Tiger beetle larvae are, like the adult beetle, extremely fast predators. They hide in burrows they dig themselves or in tree trunks and wait there for prey to wander by. Then they strike. Watch:
The larva is anchored to the walls of the burrow with spikes on its back and so has enough grip to pull in prey as big as itself. I'm sure those huge jaws help. A bigger version, if we assume that it's just as fast, could absolutely take a hapless explorer in the blink of an eye.
Take a look at the adult beetles - they are no less deadly, but absolutely beautiful.
And speaking of deadly and beautiful, here's another creature capable of snatching prey with astonishing speed, while being completely invisible before and after. The bobbit worm.
image from Wikipedia
Those brownish things beneath the antennae? Those are its jaws and they are perfectly capable of cutting a fish in half.
Bobbit worms are nocturnal creatures and occassionally they find their way into aquariums, where they can wreak havoc undetected for quite a while
Both are great for shaking the group up a bit. There needs to be at least one redshirt NPC there who gets to be the sacrifice, but I think it would work if the group is travelling with a caravan, is part of a bigger explorer team or whatever floats your boat. The sudden disappearance of a travel companion can be solved quickly or it can take a while when the players don't spot the burrow of the beast. Then it can be very creepy because who knows what happened and who is next.
Strange Beasts List