ENDANGERED SPECIES ESSAY

I’m still here. Don’t let me go. ~Robert Krulwich

Once deemed extinct in Lord Howe Island (LHI), where they are endemic, today only 35 Lord Howe Island Stick insects (Dryococelus australis), are alive in the wild, but not in LHI.

The Lord Howe Island Stick Insect is also called the tree lobster, the name we’ll use in this article. The tree lobster has a massive genome, larger than a human genome by 25%. And yet, this stick insect will only stretch six inches long – large enough to fit on an adult human’s palm.  It’s perhaps both the largest stick insect and the rarest invertebrate in the world.

The tree lobster thrived and is endemic to Lord Howe Island. In 1916 Australian Entomologist Arthur Lea counted 68 of them in the hollow of a single tree on the island. But by the 1920s, all tree lobsters disappeared, and by the 1960s they were declared extinct.

The black rats 

Their disappearance was blamed on black rats (Rattus rattus) that swam from the British ship,  SS Makambo, to LHI when it ran aground in 1918. The rats ate the tree lobsters like candy.

They also decimated five bird species and 12 other invertebrate species. Island inhabitants saw the rats running up and down tree trunks. They spoiled human food and compromised human hygiene.

LHI has some 350 permanent residents. The rodent population in 1918 rose to 300,000 rats and mice. The ratio was roughly  1,000 rodents per human.

This is a story just as much about the decimation of an entire rat population on an island, as it is about the “extinction” and rediscovery of the tree lobster.

Tree lobster rediscovered  – elsewhere

In 1964, a group of climbers navigated Balls Pyramid, a steep, rocky outcrop situated 27.2 km from Lord Howe Island. They found a few stick insect corpses that seemed to be “recently dead”.  They took pictures but left the Pyramid before nightfall.

Ball’s pyramid is very different from Lord Howe’s Island. It’s a steep and tall promontory that juts out vertically from the Tasman sea. It’s hard to climb not just because of its straight-up form, but also because it’s inhabited by barnacles, poisonous centipedes, spiny sea urchins, and other tiny, local wildlife.

Scientists decided in 2001 to find the tree lobsters. Two of them were Australian scientists, David Priddel and Nicholas Carlile. Two others were their assistants. All four rode a boat through shark-infested waters. Upon landing, they climbed 500 feet up.

But all they found were crickets. Upon heading back down, they saw a  melaleuca bush peeping out of a crack. Underneath it was fresh poop from evidently large insects.

Priddle and Carlile returned to the site after nightfall, armed with flashlights and cameras. They found 24 tree lobsters beneath the melaleuca bush, dining on tea. Aside from that, very little is known about tree lobsters in the wild.

However, they took two pairs of insects, both male, and female, to breed them in captivity. The goal was to establish an alternate population if those on Ball’s Pyramid went extinct.

As of now, only 35 adult Lobster Stick Insects live in the wild on Balls Pyramid. Because they only feed on tea, they’re endangered by the possible eradication of their food source by the invasive Morning Glory creeper, Ipomoea cairica. To thwart this, in 2003, the Morning Glory vine was partially removed from Balls Pyramid. A small portion was kept because it helps stabilize the soil of outcrops from steeper slopes.

Another threat is the possible poaching of the tree lobster and its eggs by private collectors, which is why access is restricted on the pyramid. Doing so also protects the habitat.

A third threat is natural disturbances like drought, storms, and landslides that could eradicate the entire tree lobster population in the wild, rendering them extinct within seconds.

These are the reasons why the International Union for the Conservation of Nature (IUCN) rates the tree lobster as Critically Endangered.

By 2017,  35 individuals were seen on Balls Pyramid. Surveys are infrequent because of the abovementioned vulnerabilities of the tree lobster.

Adam and Eve

The tree lobsters were brought to Zoos Victoria for captive breeding with the aim to eventually rewild them. One pair didn’t survive, so the remaining pair were named Adam and Eve by Zoos Victoria. Initially, Eve became critically ill, but the zoo staff successfully enabled her recovery, and she laid 248 eggs. The tree lobsters were fed Moreton Bay figs and alfalfa. The juveniles were given blackberries.

The entire captive population that descended from Adam and Eve numbers more than 14,000 in captivity, in Melbourne Zoo alone. Others are being bred in Bristol Zoo, San Diego Zoo in California, and other zoos and museums around the world.

Today thousands of Lobster Stick Insects exist in zoos and museums around the world. They hope to eventually recolonize Lord Howe Island, the land that’s their natural home.

Genome and differences measured 

There are morphological differences between the Lord Howe Stick Insect before its extinction, and the same insect in Balls Pyramid today. These differences raised questions about whether the two were of the same species.

To settle the issue, Alexander S. Mikheyev et. al. assembled a complete mitochondrial genome from a tree lobster in Balls Pyramid and compared it to a mitochondrial genome from a stick insect museum specimen that lived on Lord Howe’s Island before their extinction.

Results showed less than 1% difference between both genomes, falling within range to be considered the same species. It was safe to say that the tree lobster was no longer extinct.

As for their physical differences, scientists mused it could be due to genetics or the environment. By raising them in captivity, they could observe this insect regularly, and they noticed that it evolved frequently. They believe it was for morphological convergence, meaning, each tree lobster would morph and still remain similar to one another. The morphing of insects is usually an adaptation to a shared environment.

Another possibility is that tree lobsters from Ball’s Pyramid and those from Lord Howe Island both had a shared origin, but the tree lobsters at Ball’s Pyramid were perhaps isolated for a very long time.

How they got to Balls Pyramid

Another question was how they reached the Pyramid. It is the remains of a former, far larger volcano. Now it’s a steep, vertical, rocky cliff that rises 560 meters above sea level.

True, the Pyramid is less than 30 km away from LHI, but this insect can neither fly nor swim, and no land bridge connects them. Scientists theorized that birds may have mistaken them for twigs, and flew them to Balls Pyramid where they built their nests.

There’s a precedent to this theory. Scientists in Japan studying another stick insect species noted that even if birds eat stick insects, the insects’ eggs can pass through the birds’ digestive tracts and hatch. Extrapolating from this, it may be that unborn offspring was “airlifted” to Balls Pyramid, and repopulated there.

Rat story

There’s the hope of rewilding the tree lobster on Lord Howe Island where they truly belong. In fact, the Lord Howe Island Board decided in 2019 to undertake the biggest Rodent Eradication Program (REP) in the world. Strategies included:

  • Eliminating mice and rats simultaneously, to derive the best long-term results from REP.

  • Distribution of rat baits by hand, and setting up bait stations in residential areas.

  • Setting up over 23,000 rat baits inside all buildings, and throughout the island.

  • Dropping 42 tons of poisoned cereal from helicopters on areas highly populated by rats.

  • Dropping by helicopter 22,000 lockable traps that held rat poison over uninhabited, hard-to-reach mountains and forests.

  • Arming worker teams with GPS trackers to log rat movements on their mobile phones.

  • Enlisting the expertise of dozens of scientists.

The task wasn’t easy. There were some 200,000 rats on the island, running up tree trunks, destroying gardens, and disturbing the natural environment. In the end, they killed 300,000 rodents.

Paradise found

The REP was highly successful, and currently, the task is to make sure that there are absolutely no rats left on Lord Howe Island and to ensure that the rodents don’t make a comeback.

In April 2021 an island resident reported that she saw two adult rats on a road. After they were hunted and killed, they discovered that one rodent was male, and the other one was a pregnant female.

Every few months, rat detection dogs inspect the island. The most recently seen rat was caught by a detection dog in August 2021. The goal now is to make sure the rats are gone for good and to ensure that they don’t make a comeback via boats and other means to reach the island.

With the eradication of the rats, new fruit that has never before been seen by residents now grows, and people have photographed hundreds of unfamiliar insects and sent their photos to the Australian Museum. Also, four snail species previously presumed to be extinct have resurfaced.

Hank Bower, World Heritage manager of the Lorde Howe Island Board Environment, has lived on the island for 15 years.  He told the Sydney Morning Herald, “Everything is blooming, all the plants are flowering and we are seeing a carpet of seedlings.”

Ecological importance

In general, stick insects are like gardeners. By feeding on leaves, they prune shrubs, in this way allowing new plants to grow. Their defecation builds up soil nutrients that will enrich succeeding new plants. This activity permits forest recycling.

They also play a vital role as the prey of certain meat-eating amphibians, birds, some mammals, and several reptiles. The latter, by only eating meat, are deprived of necessary nutrients from the sun that plants generate through photosynthesis.

By feeding on plant-eating insects like the tree lobster, these animals are able to absorb the valuable nutrients of the son through this and other insects.

When meat-eaters prey on the tree lobster, they absorb valuable energy and nutrition that is generated by the plants that these insects eat.

In sum, the tree lobster is equally valuable in its diet, and as prey. In the latter case, it links sun-generated energy derived from plants and transposes it to the animals that eat it. In this way, the tree lobster passes the sun’s energy up through the food chain.

It may sound heartless, but according to entomologist Matan Shelomi, insects have no pain receptors, so they can’t feel pain, but irritation. If damaged, they have no emotions, implying that they can’t suffer. So dying isn’t torturous, for them, it’s inconvenient.

We hope Shelomi is right, but there are conflicting beliefs on this. Some studies show that insects have a wider range of emotions than we realize. It’s also suggested that they can feel delight, depression, fear, and respond to pain.

The bottom line is that everybody dies, and in death, a role is played in the well-being of an ecosystem. And in this sense, tree lobsters are no different from all the rest of us.