KNOXVILLE, Tenn. — Zoo Knoxville welcomed a Critically Endangered Spider tortoise hatchling this week. 

The process takes time. The National Zoo says the tortoise eggs have to incubate for about 220 to 250 days before hatching.

During that time, Zoo Knoxville says the baby has to absorb the yolk before emerging from the egg.

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The critically endangered spider tortoise lives only in Madagascar, where it is the smallest of four native tortoise species, according to the National Zoo. It is named for the web-like pattern of yellow lines on its dark brown or black carapace.

Spider tortoises are also subjected to poaching and illegal collection for the international pet trade.

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Little is known about spider tortoise reproduction. The National Zoo says when the wet season arrives and their dormancy period ends, they begin to look for a mate. Female spider tortoises only lay one egg per clutch, according to experts, so populations cannot quickly recover from a decrease in numbers. 

The Smithsonian's National Zoo said it successfully hatched two spider tortoises in 2015, a remarkable accomplishment given how challenging it is to breed this species.