Trapdoor spider

Digging door builder

Although called trapdoor spiders, not all of the 50 species of the Ctenizidae family build a hatch to their burrow.

Appearance and characteristics

The jaws are adapted to dig with. Even when very small, these spiders dig a burrow and often provide the entrance with a round, tightly closed door equipped with a hinge of silk. The door is skilfully masked with soil, moss, branches, grass and other adjacent material and is often impossible to detect if it is not open. As the spider grows, the burrow must be widened and the door made larger along the outer edge. If you look closely you can see these door enlargements that are similar to annual rings on a sawn tree trunk.

Feeding and catching

The spider patiently waits in the hole with a pair of legs against the closed door. On the ground outside the door, it has tightened up triple threads that lead into the burrow. When the spider senses vibrations in the threads, it pushes the door open and throws itself over its prey which is killed by a bite of the jaws which are in contact with venomous glands. The poison contains enzymes that dissolve the victim's tissues so that the spider can then suck in the nutritious soup. Despite its kinship with the funnel-web spider, the trapdoor spider's venom is not at all as strong but is sufficient to kill the small insects that are on its menu.

Reproduction

The females stay in their burrow almost all the time. The males visit the burrows of the females prior to mating and usually, strangely enough, avoid being eaten. The females then guard the eggs and feed the young with regurgitated food. Like their relative the funnel-web spider and some other primitive spider species, the trapdoor spiders breathes with two pairs of book lungs. More modern spiders often have a pair of anterior book lungs and a pair of rear tracheas. In several small spider species, the anterior pair of book lungs has also been replaced by tracheas.