A Hard-Charging Spider Without a Web

A Hard-Charging Spider Without a Web

Illustration by Adelaide Tyrol

If the man in the film who explained, “Honey, I shrunk the kids,” turned his attention to you, and you ended up one centimeter tall and found yourself on the lawn, you would have your work cut out for you. You crouch under a clover leaf trying to comprehend a strange world. Grass blades bend as a young grasshopper—the size of a calf in your present scale—approaches and nibbles a stalk of grass.

An indistinct tapping grows more pronounced as a dark, hairy creature appears, seemingly the size of a bear. It creeps forward, bending around a stone to peer ahead. Seeing the insect, it freezes. Sunlight reflects off iridescent blue-green appendages folded beneath its head, each bearing a needlelike fang. You stare into a pair of huge dome-shaped eyes. Another smaller pair looks out at an angle from each side of the head, a third pair faces straight out to the side, and a tiny fourth light-sensitive pair is almost hidden.

This is a jumping spider, a salticid, a predator that hunts by stealth rather than by spinning a web. Its immense forward-facing eyes, unlike those of all other spiders and insects, form precise telescopic images whose meaning is sent to a large brain.

Oblivious to danger, the grasshopper lazily waves its antennae. The spider is a dozen grasshopper-lengths away, and catlike, it hunches down, rear legs folded underneath as it adjusts itself, moving slightly from side to side. Its large eyes, serving now as rangefinders, gather information about distance. The third pair of legs provides stability while the first two pairs extend out in front. All is quiet. Then, faster than your eye can follow, the spider launches itself with a single prodigious leap, trailing behind a lifeline of silk anchored to the ground. Its furry body lands solidly on the grasshopper. Instantly aroused yet unprepared, the insect’s powerful rear legs are not cocked. Immobilized, it goes nowhere. The spider enfolds it and injects paralyzing venom through twin fangs.

The toxin liquefies the victim’s tissues, and the spider begins feeding, its large stomach pumping rhythmically, drawing nourishment into empty chambers extending into its eight legs.

You creep away. Whether a dream or a spell cast by the man who shrank his kids, you return to your own world, towering over the miniature jungle at your feet.

Each species of jumping spider has a language all its own to communicate with others of its kind. With 4,000 species of salticids worldwide, such distinctions are necessary to avoid living in a veritable Tower of Babel, especially when a male invites a female to bear his young.

Males also “speak” to other males; one will warn another with intimidating body-language as he edges sideways, legs held in formalized position, abdomen bent almost parallel to his adversary, displaying his size and readiness to fight. Held aloft, the under sides of a jumping spider’s front legs may be colored or iridescent, a living billboard ensuring positive identification.

There is no confusion of identity, for one species cannot understand the ceremonial dialect of another, so mistaken mating doesn’t occur.

A courting male’s message is conveyed to a female mostly with his front legs, perhaps adding another pair for emphasis. Acrobatics become a frenetic invitation. He rears back on his hind legs, swaying and lunging and rocking sideways, waving enlarged front legs straight out, semaphoring and zigzagging, up and down, dancing back and forth in ritualized fashion.

As a male prances in front of a female, she watches his posturing intently, answering with slender front legs as the dialog continues. If she is receptive, she still may play hard to get, darting off or engaging in a mock attack, eventually lowering and bending her abdomen toward him. They circle one another in an elegant minuet. Another male of the same species, his huge eyes picking up every signal of the elaborate courtship, avoids conflict and moves away.

Jumping spider territories are extensive and may include tree trunks, rock walls, and open meadows. Being “out on a limb” is no problem; as a salticid leaps into space, thrust forward by hind legs now stretched to the rear, a trailing strand of silk is anchored to the branch and drawn by the spider’s momentum from spinneret glands at the tip of its abdomen. The silk is a safety line in case the spider needs to return to its original perch. If so, it catches the thread with comb-like claws and skims back to the branch it has just left. Otherwise, the lifeline is severed or consumed, because protein in spider silk is not to be wasted.

Catlike jumping spiders, with their brilliant colors, agility and apparent intelligence, are enormously appealing—if only a child doesn’t say, “Hey, Mom, I just shrunk Grandpa!”

Bill Amos of St. Johnsbury, Vt., is a retired biologist and author.

 
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