Feature

Lifestyles of the Small and Hairy

Spiders are remarkably sophisticated creatures...

Dr Simon D Pollard

At the end of the 1958 insect classic The Fly, a scientist, who has swapped heads with a fly, gets stuck in a garden spider's web. As the spider walks across its web towards the struggling insect, the tiny human head cries "help me, help me", in a voice reminiscent of a soon-to-be-retired choir boy. A colleague who hears the screams, puts the insect aside and thinks of his friend's fate. Euthanasia with a rock follows, but regrettably the spider is also killed.

Only on film and in our nightmares are we small enough, or the spiders big enough, to make gardens terrifying. While we sniff flowers, curse weeds and rake leaves, we seldom see spiders as they detain, dismember and devour insects, delude and deceive each other, and are dismantled by other predators. This story looks at gardens from a spider's perspective.

Lean and green, New Zealand lawns are often manicured with the same fastidiousness as a closely cropped beard. In North Canterbury, many lawns are covered with grass-lined, hinged trapdoors, built by trapdoor spiders which live in a silken tube beneath; but, like trolls under a bridge, they listen for victims above.

The spider waits with its front legs poking out from beneath the lid and when an insect walks by, the trapdoor flies open. The spider then explodes out of its burrow, buries its fangs into the prey's body and pulls it down the tube. The remains of victims are periodically discarded in grim rubbish piles next to the trapdoor.

Most trapdoors are too low for lawnmowers and while the grass growing on the lid may get shorn, the spider's home remains intact. I wonder how many trapdoor spiders have interpreted the vibrations from lawnmowers as the "mother of all beetles", optimistically flipped their lids and pounced into oblivion.

If trapdoor spiders resemble trolls, then Supunna picta, a black-and-white hunting spider with orange legs, is definitely the roadrunner of the spider world. In between brief periods of being still it runs frantically over walls and vegetation, as if it is a wind-up toy out of control. It literally runs down its prey, often flies that have paused between flights.

This hyperactive behaviour doesn't stop when it feeds, and like a dog with a soft toy, it pulls the stuffing out of its prey. Dismembered body parts litter its feeding ground and often the prey is in so many pieces it is difficult to know what type of insect it was. It would definitely be a closed coffin at the funeral one of Supunna's victims.

Trolling for Food

Spiders that build webs have more in common with trolls than roadrunners because they wait for their food to come to them. Although spiders do not fly, a lot of their food is derived from insects that can. The evolution of the orb-web, and other webs that act as aerial filters, has allowed spiders to exploit a food source that would otherwise be out of reach.

Webs effectively amplify the size of the spider and provide it with information that would normally be outside the range of its own senses. Just as binoculars extend our visual range, a spider's web extends the range over which the vibrations of an insect can be detected. By adding glue droplets to the silk, prey remain entangled in the web.

The cartwheel-shaped web of the common orb-web spider, Eriophora pustulosa, is seen in gardens throughout New Zealand, with morning dew often hanging from the silken threads, like gigantic globs of glue. At night the web is either remade or repaired, after which time the spider waits for insects to fly into the web and become stuck.

The "spokes" of the web do not have glue droplets and are used as attachment points for the sticky spiralling threads. When an insect is trapped, the spider rushes out and wraps it in a shroud of silk, ensuring the food parcel does not escape. On a busy night, wrapped insects litter the orb-web like gruesome trophies displaying the spider's hunting success.

Tiny Tarzan

Sometimes it is not only the orb-web spider that is listening for an insect crashing into its sticky threads. A tiny two-millimetre spider called Argyrodes antipodiana often lives on the periphery of orb webs, and it also responds to the struggles of trapped prey. Argyrodes is a "kleptoparasite" that steals food caught in the orb-web. Rather than taking minute insects that have been trapped and ignored, it feeds on large prey being eaten by the host Eriophora.

When Argyrodes feels vibrations from a struggling insect, it starts to move across the web. Once Eriophora is feeding, Argyrodes moves right up and steals food from its competitor's mouthparts. Although both spiders have very poor eyesight, the vibrations of the little kleptoparasite moving on the silk are sometimes detected, and it risks being eaten. If it is fast enough, the tiny thief can swing away, like Tarzan, on a silk safety line attached to the outside of the orb web.

Probably the most common web-building spider in New Zealand is Badumna longinquus. Its cobwebs, with a narrowing tubular retreat that disappears into a crevice, line the outside walls of houses throughout New Zealand. Unlike the familiar orb-web, the web of Badumna does not have glue droplets that trap prey. Instead, the spider applies a fine "wool" of threads in a zig-zag pattern between structural threads. Prey become entangled and seal their doom by transmitting their attempts to escape down the line to the spider's retreat.

For over a year, a female Badumna had her web attached to the bathroom basin in my house. When I brushed my teeth a spray of minty foam would land on her web. This must have felt like a flock of small flies arriving, since she would rush out and attack a few bubbles, before retreating to ponder how a bunch of flies could turn into hollow peppermint-flavoured balls.

Both toothpaste and the infamous white-tailed spider Lampona cylindricata can trick Badumna into racing out of its retreat. While being deceived by the former only causes minty breath, the latter ends in death. Lampona catches other spiders by using its legs to mimic the vibrations of struggling prey. When the unsuspecting spider rushes out to dine, it becomes dinner. Recently, when I was driving in the United States, an electronic billboard beside the freeway flashed the message "the family that prays together, stays together". While I should have thought of family values, I actually imagined a family of praying mantises hunting in a group. But, back in the real world, mantids prey alone.

As a praying mantis walked over a shrub in my garden, it reminded me of a graceful Godzilla in a Japanese horror film. It stopped, as if it was a church-going insect, raised its forelegs piously and became motionless. A jumping spider was moving towards it. Although the spider had excellent eyesight, its tiny brain had not registered the green shape of the mantid as anything other than a leaf. When the spider was within reach, the mantid's forelegs changed from a praying stance to a preying one and snatched the spider from the leaf. Like a wilful child dismantling a toy, the mantid pulled the spider's legs off and ate them.

Although thousands of small hairy bodies with unblinking eyes and spindly legs live around us, we usually only catch glimpses of their lives. However, next time you see a spider's web in your garden, take a closer look. There may be somebody in it you recognize.

Dr Simon D Pollard is Curator of Invertebrate Zoology at Canterbury Museum.