Keepers at San Diego Zoo are currently looking after 500 Lord Howe Island stick insect eggs in an effort to save the critically endangered bug, often called the 'rarest insect in the world'. The giant bug, also known as a 'tree lobster', was thought extinct after rats invaded the island in the early 20th century.

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But in 2001, scientists happened upon an incredible discovery – a few dozen of the insects on a nearby island. Now conservationists are trying to rebuild the population and save Dryococelus australis from extinction.

San Diego Zoo now has a breeding program of 40 female and 29 male insects, who came from Australia at the beginning of the year.

"We've reached a really important milestone in the Lord Howe Island stick insect breeding project," said associate curator Paige Howorth. "This is the only group of Lord Howe Island stick insects in North America and the fact that they're breeding is a really exciting development."

Howorth said that the San Diego Zoo group is meant to become a "assurance group" to the insect at Melbourne Zoo – "the primary group of animals on the planet".