Free The Flight of the Iguana by David Quammen

greenhouse, and had to lament that “I cannot make the little creature grow well.”
    He needn’t have been hard on himself about that, because the Venus’s flytrap is drastically finicky about its habitat. There is only one species, and that species confines itself to only one native range: a narrow strip of coastal plain in the Carolinas. The flytrap is so sensitive to its own habitat requirements that, even within such a small range, it can survive only in very particular types of terrain. More about this choosiness in a minute.
    Despite its rarity, the Venus’s flytrap is the most famous of carnivorous plants, and we are all roughly familiar (we think) with its general anatomy and behavior. Each leaf is modified to the shape of a leg-hold trap, two semicircular lobes on a hinge, cocked open invitingly but ready to slam shut the instant a trigger is tripped. Right? Along the rim of each lobe protrude those needle-like spines. Maybe they can’t stab an escaping fly, as once thought, but they certainly add to the aura of implacable malice. Right? The inner surfaces of the lobes are cobbled with tiny liquid-filled glands, some of which show a mysterious red coloring, some of which exude a clear nectar. An insect is attracted by the color and smell, lands on or crawls into the open trap, and then—the heart-sinking snap. The insect’s demise is ugly, remorseless, and sudden. Right?
    Well, yes and no. The reality is more complicated and more interesting.
    The flytrap’s anatomy includes a few ingenious features that allow it to measure and taste its potential prey before committing itself to the meal. This plant is no heedless glutton. On the contrary, its behavior is forbearing and judiciously economical.
    First the question of taste. Those reddish glands crowded onto the flytrap’s palate secrete a digestive fluid, a mixture containing weak acid and an enzyme called proteinase, which dismantles animal protein. Once the animal protein has been broken down into soluble fragments, that nutritious solution can be reabsorbed by the plant. But unlike the pitcher plants (which hold a permanent reservoir of digestive fluid, into which victims fall), the flytrap remains dry-mouthed until a morsel of prey has been caught. Furthermore, it isn’t to be fooled by poor substitutes. It responds only to real food. The lobes close on a cricket or a fly—and the proteinaceous saliva begins flowing. The lobes close on a small gobbet of raw beef—here also the saliva begins flowing. The lobes close in reaction to the touch of a glass rod, or the tip of a pencil, or the weight of a pebble fed to it just like the beef—and nothing at all happens. The plant does not waste its time or its juices.
    It isn’t receiving the right signals of chemical feedback. In other words, the pebble tastes wrong. Still dry-mouthed, the flytrap opens its lobes again as soon as possible, resuming the wait for a genuine meal.
    After a false alarm, the plant is ready again in less than twenty-four hours. If the chemical signals are positive and the chamber floods with digestive fluid, on the other hand, five to ten days will pass before the flytrap can reopen. That difference in the expenditure of resources (time and digestive fluid) seems to be why the plant also measures its prospective victims, and proceeds or refrains accordingly. It simply refuses to bother with insects that are too small to be worthwhile.
    The measuring is done in two ways. One is inherent in the structure of the triggering mechanism. On the inner surface of each lobe, among the digestive glands, are three sensitive hairs that serve as trip wires for the trap. Merely touching one hair, though, is not sufficient to spring the trap. At least two distinct touches (upon the same hair or different ones) are required, and those touches must occur no less than about one second nor more than about twenty seconds apart. The hairs themselves are