The Spider and the Wasp

"The Spider and the Wasp" from Scientific American [August 1952]

Alexander Petruckevitch (1875-1964)

A fertilized female tarantula lays from 200 to 400 eggs at a time; thus it is possible for a single tarantula to produce several thousand young. She takes no care of them beyond weaving a cocoon of silk to enclose the eggs. After they hatch, the young walk away, find convenient places in which to dig their burrows and spend the rest of their lives in solitude. The eyesight of tarantulas is poor, being limited to a sensing of change in the intensity of light and to the perception of moving objects. They apparently have little or no sense of hearing, for a hungry tarantula will pay no attention to a loudly chirping cricket placed in its cage unless the insect happens to touch one of its legs.

But all spiders, and especially hairy ones, have an extremely delicate sense of touch. Laboratory experiments prove that tarantulas can distinguish three types of touch: pressure against the body wall, stroking of the body hair, and riffling of certain very fine hairs on the legs called trichobothria. Pressure against the body, by a finger or the end of a pencil, causes the tarantula to move off slowly for a short distance. The touch excites no defensive response unless the approach is from above where the spider can see the motion, in which case it rises on its hind legs, lifts its front legs, opens its fangs and holds this threatening posture as long as the object continues to move.

The entire body of a tarantula, especially its legs, is thickly clothed with hair. Some of it is short and woolly, some long and stiff. Touching this body hair produces one of two distinct reactions. When the spider is hungry, it responds with an immediate and swift attack. At the touch of a cricket’s antennae the tarantula seizes the insect so swiftly that a motion picture taken at the rate of 64 frames per second shows only the result and not the process of capture. But when the spider is not hungry, the stimulation of its hairs merely causes it to shake the touched limb. An insect can walk under its hairy belly unharmed.

The trichobothria, very fine hairs growing from disklike membranes on the legs, are sensitive only to air movement. A light breeze makes them vibrate slowly, without disturbing the common hair. When one blows gently on the trichobothria, the tarantula reacts with a quick jerk of its four front legs. If the front and hind legs are stimulated at the same time, the spider makes a sudden jump. This reaction is quite independent of the state of its appetite.

These three tactile responses—to pressure on the body wall, to moving of the common hair, and to flexing of the trichobothria—are so different from one another that there is no possibility of confusing them. They serve the tarantula adequately for most of its needs and enable it to avoid most annoyances and dangers. But they fail the spider completely when it meets its deadly enemy, the digger wasp Pepsis.

1. The primary purpose of the passage is to:

A) report on controversial new discoveries about spider behavior

B) summarize what is known about the physical and social responses of tarantulas

C) challenge the findings of historic laboratory experiments involving tarantulas

D) discuss the physical adaptations that make tarantulas unique

2. It can most reasonably be inferred from the opening paragraph that tarantulas

A) become apprehensive ad sudden noises.

B) depend on their mothers for nourishment after hatching.

C) must consume insects or millipedes daily.

D) are reclusive by nature.

As used in paragraph 2, "excites" most nearly means

A) enlivens.

B) inflames.

C) stimulates.

D) awakens.

As used in paragraph 4, "independent" most nearly means

A) self-sufficient

B) self-governing

C) impartial

D) regardless