The brave stick insect from Lord Howe Island crawling on the gloved hand of Kyle Kassel, a keeper at the San Diego Zoo, I had no idea it shouldn’t exist. He ran through Kassel’s hands like a hyperactive dog.
Nicknamed tree locust because some reach 20 centimeters, this insect has also been called “the rarest invertebrate in the world” after it was on the brink of extinction. But there it was, in the Zoo’s McKinney Family Invertebrate Propagation Center, evidence that an effort, led by Australia’s Melbourne Zoo, may be able to pull Lord Howe’s stick insect back from the brink.
Insects receive less attention than their charismatic vertebrate cousins, such as tigers and pandas, but they play critical roles in ecosystems as pollinators, predators, prey, and decomposers. The Lord Howe Island stick insect is not as striking as other members of the order Phasmatodea, but what it lacks in flashy wings or bright colors it makes up for in charm.
Lord Howe Island is located about 600 kilometers east of mainland Australia and was discovered in 1788 by a British naval officer, Henry Lidgbird Ball. Human settlement followed in 1834. In 1918, a trading ship accidentally released stowaway rats, and by 1921 the island’s stick insects had disappeared.
In 1964, a climber discovered a dead one on Ball’s Pyramid, an islet about 23 kilometers southeast of Lord Howe Island. Subsequent efforts to find live stick insects there were unsuccessful until 2001, when a search party found two females in a tea tree. The entire population of tree locusts, about 24 individuals, was clinging to life there.
In 2003, the Lord Howe Island Board, working with the New South Wales Government, sent scientists to collect pairs of Ball’s Pyramid stick insects to give them to experts who could breed them.
“They chose Melbourne Zoo because of our expertise with invertebrates,” said Kate Pearce, who has overseen the zoo’s stick insect program since 2011. The Melbourne team learned how to care for their pair, called Adam and Eve, through testing. and error.
Patrick Honan, Pearce’s predecessor, spent the night with Adam and Eve to monitor their well-being. Eve was reluctant to lay eggs; she ended up “getting pretty bad,” Pearce said. Honan mixed a “magic elixir” of sugar, calcium and ground tea tree leaves, and then poured drops of the concoction into Eva’s mouth. After keepers placed a sand tray in her enclosure, she laid eggs there. Most stick insects drop their eggs from a branch to the ground, but Eva preferred the sand.
These initial efforts paid off, as Melbourne Zoo now maintains a population of around 500 stick insects. In 2017, he brought in another female from Ball’s Pyramid to diversify the gene pool in captivity.
Melbourne sent the San Diego Zoo a batch of eggs in 2012. About 20 percent hatched, but none of the chicks survived. In 2016, Paige Howorth, curator of invertebrates, went to collect more eggs. But that population was not achieved either. A shipment of 600 eggs in 2022 led to the zoo’s current count of at least 400 individuals.
Raising invertebrates is cheaper than raising pandas or tigers, but it’s not easy. Melbourne Zoo grows “several thousand plants just for the stick insects on Lord Howe Island,” Pearce said. Kassel called the phasmids “voracious.”
Starting a population from a few individuals leads to inbreeding. Diseases can also spread quickly in confined spaces. And when kept long enough, the rapid reproduction of many invertebrates allows them to evolve rapidly.. A 2021 study found that Melbourne stick insects have developed smaller eyes and fewer olfactory receptors over timewhich can affect their ability to survive in the wild.
Cristina Venables lives on Lord Howe Island. In addition to caring for a captive colony of stick insects, she is preparing the island for her potential return. Although many of the 445 residents are proud of the native fauna, others are concerned about what life would be like with the insects. “There is no one alive who has lived with phasmids on the island,” Venables said. Therefore, stories about them crawling noisily across rooftops or knocking leaves off trees “can take on a life of their own.”
Venables plans to invite the community to visit their potential new neighbors and even help care for them “so they can see what phasmids are all about.”
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