Trap, Trickery and Tragedy

The trapdoor spider is a medium-sized spider that keeps itself safe by constructing an underground retreat with a cork-like tight fitting door made of soil, vegetation and silk.

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Trapdoor spider; Image source: Wikipedia

Using its powerful jaws, it excavates a vertical shaft about a feet deep, and measuring 1.5 inches in diameter. The walls of this tunnel are lined with a sheet of silk, and the trapdoor is built up using layers of soil and silk

The trapdoor is camouflaged by the layers of leaves and moss around it, and is hinged on one side only with silk! Usually nocturnal, it waits for prey below the shut door by holding the underside using its claws. The spider is so intelligent that it even makes special holes on the inside of the door so that it can get a proper grip.

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Image source: Animal Corner

When insects, other arthropods, or small vertebrates disturb the ‘trip’ lines laid by the spider around its trapdoor, the spider is alerted that a meal is within reach. It detects the prey by vibrations, and when the prey comes close enough, the fierce spider leaps out of its burrow to quickly seize the helpless prey, which is then taken below, through the tunnel. Ingenious!

A hungry individual never leaves its burrow completely, preferring to wait halfway outside.

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The trapdoor, while protecting the inhabitant spider from intruders and enemies, also serves to shield the insect’s burrow from dust and vegetable rubbish.

When a female displays aggressive reactions whenever the male approaches it, the latter can overcome it although it is not precisely known how.
Also, females never travel far from their burrows, especially if they have an egg sac. During this time, the female will capture food and regurgitate (vomit) it to feed her spiderlings.
When predator becomes prey
Spider wasps are known for their behavior of hunting and killing spiders, much larger in size. These wasps are solitary, and use a single spider as a host for feeding their larvae. seek out the burrows and manage to gain entrance.
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Wasp dragging a spider to its nest; Image source: Wikipedia
Upon finding the vulnerable trapdoor spider, the wasp stings it. The venom starts to act, and the spider will eventually paralyze.Some wasps only temporarily paralyze their hosts, which regain activity before being eventually killed.

However, because of the large body size of their prey, these wasps usually  either construct burrows near the site of attack or use the host’s own burrow or tunnel. The paralyzed spider is dragged to where a nest has already been built by other wasps.

Here, a single egg is laid by a female wasp on the abdomen of the immobile spider, and nest or burrow is closed, so that the larva can develop without disruption by other parasites. As a way of deterring predators from their nests, spider wasps assemble dead ants into the outermost chamber. The chemical action prevents intrusion by predators or scavengers.

As for the spider, the worst is yet to come. When the larva hatches, it devours the spider alive. The larva saves vital organs like the heart and the central nervous system for last.By waiting until the final larval instar, it ensures the spider will not decompose before the larva has fully developed.

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Wasp larva gradually eating a spider from the outside in. Image souce: Australian Museum

The spider eventually dies a horrific death.

 

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