Shufflebrain

Salamanders are born with the instinct to hunt. As embryos, yellow-white yolk stuffs their stomachs and intestines. Traces of yolk persist into the early larval periods; but within hours after the last molecules of the yolk have been consumed, thus clearing the alimentary canal for a meal, the larva is ready to strike at any prospective quarry. Although feeding is instinctive, behavioral nuances may be imprinted during early encounters with prey. The greater the struggle at the stage when feeding begins, the more finesse the larva seems to show in subsequent attacks. But animals deprived of early attack experiences still hunt later on, only with less elegance and efficiency.[1]

The active nature of the salamander's feeding is apparent in its movements in relation to different kinds of prey. When it is preying on water fleas, daphnia, or brine-shrimp embryos--any creature that jets through the water in jerky little spurts--the salamander larva waits motionlessly, poised until the victim comes close to its snout. Then, snapo! The larva's move is quick, sudden, accurate and deadly. Then it settles down to wait for more!

But with wriggling worms, such as tubifex or their cousins, the milk-white encyhtreas, the salamander's response is quite different. When it first senses a worm, it freezes, hangs suspended in the water like benign debris, or stands stock still at the bottom of the bowl. Moments may pass as it seems to be fixing the location of the worm. Then slowly it turns, usually pausing again, perhaps to recheck the azimuth of the prospective course. Half-walking, half-swimming, it now glides cautiously toward the fated worm. At its destination, it usually pauses once more and carefully, deliberately, moves its head back, forth and around the undulating mass, as though computing the tensor algebra of the quarry's ever-varying geometry.

I have seen this sizing-up stage last thirty or forty seconds, a seeming eternity in the waiting game. The salamander takes one last momentary pause. Then comes the strike. And into it, the salamander throws every bit of its might. The attack is not the "blip," as with brine shrimp or daphnia but a ferocious, violent assault that would knock down a building, if the salamander were the size of a great white shark. It locks the worm in its jaws and hangs on, no matter what escape maneuver the squirming victim tries; and it swallows the worm, live, bit by bit. If the worm is relatively short, it goes down quickly. If not, the process may take minutes, the salamander holding on with such tenacity that it can actually be lifted from the water by the free end of the catch.

Salamander larvae sense their prey in three known ways: sight, touch and sonar--shock-wave detection-- via what is called the lateral line system. The larva has the anatomy for smell, but by all indications it doesn't use this sense until close to metamorphosis into a land animal. It can use its other senses either singly or in any combinations, but it has a very strong predilection for the eyes, when it has them. For example, an animal with only one eye will turn, twist and aim the eye for a good look at a worm before making a strike. Yet an eyeless salamander can use either sonar or touch, or both, to launch a completely successful attack.

The salamander's capacity to endure massive injury has fascinated biologists ever since 1768, when Lazzaro Spallanzani published the fact that salamanders regenerate lost appendages. In larvae, a fully functioning replica replaces an amputated leg or tail in a month to six weeks; in adults, the process may take a year or more. Regeneration occurs again and again following subsequent amputations, as Spallanzani, no less, reported. Other organs and tissues regenerate as well. A severed optic nerve, for example, reestablishes contact with the brain, and the eye eventually can see again. In fact, almost all the salamander's nerve fibers grow back. Following an incision into the brain, new nerve fibers quickly sprout and soon reknit a completely functional patch across the rift.

Larval salamanders are also excellent recipients of tissue and organ transplants. They do possess tissue-rejecting mechanisms, but rejection is very sluggish and inefficient and often fails completely, the foreign graft becoming a permanent part of the host animal.