The Icecrawler is an ice-dwelling, almost woodlouse-like quadrupedalien from Glacier Cap North, on Darwin IV. It was first discovered upon the northern glacier itself near the tundra-fields of the Planum Hudson in December 2359, during the First Darwinian Expedition.

Icecrawlers can leave behind many drag marks crisscrossed on areas of the glacier not unlike those of the foothill-dwelling Keeled Sliders. The scale of the tracks and the forelimb strokes are dissimilar, however, and the two species are as well. There will also be innumerable small tunnel openings in the ice cliffs. They occur in clusters but there seems to be no obvious pattern to their distribution.

These creatures can be found on the foreboding expanse of the glacier's surface in large groups (usually 30-odd). From a distance of some 50 kilometers away they might be mistaken for blocks of ice instead of life forms.

Each individual Icecrawler, while found motionless in their winter hibernation, is imbedded in a translucent sac which, in turn, can be frozen to the glacier's surface. These sacs are roughly three meters long, smooth, rigid, and ovoid. They appear to have been in place for some time. Though the sacs are somewhat translucent, it is difficult to discern the shapes of the core-creatures within. Something can sometimes be seen to stir, but scanners of the Expedition have given back only the weakest of signals, most of the scanner beams bouncing off of the strange, impermeable sacs.

Weeks pass and by early arctic spring most Icecrawlers in a group will be gone, leaving only a small number of individuals behind in the same spot. All but one or two of these left-behind individuals will be free of their sacs and their transformation is remarkable.

Instead of the cryptic, featureless ovoids that had at first confounded the Expedition, now appearing are armored creatures busily ingesting their outer sacs. Each positions itself over the discarded and shriveled sac and unseen mouthparts suck the membrane down until eventually nothing remains.

The last one or two individuals in these groups have waited, it seems, to demonstrate the discarding process at a different time. In order to break free of a hibernation sac, the somewhat deflated sac begins to expand. Apparently inflated by the creature's exhalations, the sac grows to startling proportions before bursting, with a comically flatulent roar, in a cloud of frozen vapor. The internal pressure must be considerable; a 20-minute rest, accompanied by much vaporous panting, is evidence of the animal's exertions.

The Icecrawlers fully revealed are almost as enigmatic as they had been in their sacs. No legs or feet or even head are visible; each animal is covered with tightly-joined yet flexible armor plates. With no features to show it is hard to even distinguish head from tail.

As the creatures finish eating their own sacs, they begin to move over the ice with surprising speed, each one leaving an unnaturally slick trail behind. Only their movement gives any clue as to which end is the front. As they move off, there are many straight trails etched into the ice, corresponding, it is assumed, to the many absent Icecrawlers of the group.


The underside of the Icecrawler shows its crescent-shaped mouth, which shaves the ice as it crawls. Both the Icecrawler and the Icedart are believed to be sub-varieties of Darwin IV's air-sifters which find their microscopic nutrients in the frozen water vapor rather than air.

The two-meter-long animals slide their way over the ice in very unpredictable patterns. Their speed, approaching 35 kilometers per hour, seems incredible for an animal with no visible legs or propulsion system. They zigzag across the surface of the glacier. They can head toward a patches of brownish alga-rich ice. When they reach the patch, they slow to a halt. As in the case of their unseen limbs, now at work are their unseen feeding organs as the Icecrawlers begin to graze on the algae, leaving strange scalloped grooves behind them in the ice.

After feeding, they are always on the move, leaving the glacier sculpted by their scalloped feeding tracks and locomotion marks, and littered with their fecal coils.