The cunning ingenuity of the trapdoor spider

This edited article about the trapdoor spider originally appeared in Look and Learn issue number 110 published on 22 February 1964.

Trapdoor spider (bottom right)

All the 50,000 species of spider are strange creatures, but trapdoor spiders are the strangest of all. Although they spend most of their life underground, their first venture in the world is to travel by air.

A few weeks after a family of spiderlets have hatched out of their eggs and are strong enough to move about, they form up in single file and march off to a tall bush or tree. Then they climb up to the top, throw out some silken threads, and are carried away by the breeze.

Just how far they fly or balloon along in this way depends upon the air currents. Sometimes they travel for many miles, but usually they drop back to earth after a flight of only a few hundred yards.

Spiderlets’ air voyages are a wise precaution by nature to make certain that they have a reasonable chance of growing up. Adult trapdoor spiders are terrible cannibals and most of the youngsters would be eaten by their parents if they did not leave home.

Wherever it may land, the young trapdoor spider immediately sets to work and digs a shaft or tunnel into the ground. It does the job with its own built-in tool: a rake consisting of rows of thin but very strong bristles arranged like the teeth of a comb and growing from the jaws.

As the grains of earth are loosened, the spider spins silk thread round them to make up tiny parcels which it carries some distance away from the tunnel. This prevents wasps, centipedes and other enemies from finding the excavation.

When the tunnel has been dug to the depth of an inch or so, the spider covers the opening with a lid made from grains of earth held together with silk web. The lid has a bevelled edge so that it fits tightly over the hole like the plug of a bath.

Next, silk thread is spun along one edge of the top of the lid. The other ends of the threads are fixed to the ground to make a hinge.

On the underside of the trapdoor, the spider drills two holes. These form handles into which the spider places its legs to pull the door shut.

The holes are also used to lock the door. If an enemy tries to force a way into the burrow, the spider slips its legs through the holes, so bolting the door.

Immediately it has finished the trapdoor the spider digs its tunnel deeper and deeper. As it works its way down, it “plasters” the wall with earth mixed with its saliva. This makes the shaft waterproof.

The “plastered” wall sets hard and smooth and is then “papered” with spider web.

Very often a second tunnel is dug to branch off from the main one.

The second tunnel also has a trapdoor. If an intruder gets past the first door it has to tackle the second before it can reach its quarry.

Sometimes, too, there is a third trapdoor opening on to the surface of the ground. This provides the spider with an escape hatch if the first and second doors are broken down.

Throughout the day the spider sits just outside its closed trapdoor waiting for the insects upon which it feeds. Immediately one comes along, the spider snaps it up, opens the trap and disappears into the tunnel for dinner.

There are more than a hundred species of trapdoor spiders. They range in size from midgets about half-an-inch across to giants bigger than half-a-crown.

All true trapdoor spiders are native to warm climates such as those of Africa, Indonesia, Malaysia and South America.