What’s A Tree Lobster? What’s A Land Lobster?

Lord Howe Stick Insect, Dryococelus australis.
Lord Howe Stick Insect, Dryococelus australis. Source: Hogan (2008)

The Lord Howe stick insect is one of the most famous single insect species. To summarise its story, it is a giant, flightless stick insect that was endemic on Lord Howe Island in the Tasman Sea, 770 km off the coast of Australia. In the 1930s , it was pronounced extinct due to excessive invasive rat predation, despite local accounts documenting them as very common and part of the island’s culture. These black rats (Rattus rattus) were accidentally introduced in 1918 when a ship ran aground on the island, and they also put the Lord Howe Island giant land snails, Placostylus bivaricosus and Gudeocoocha sophiae, at risk.

24 km SW of Lord Howe Island lies a 551 m high spire, Ball’s Pyramid. For decades, rock climbers who visited it reported remains of the insect, and a photograph of it was even taken in 1964, but the New South Wales National Parks and Wildlife Service didn’t allow proper scientific investigation of the place, most likely due to the perceived unlikeliness of anything so spectacular existing there. This situation remained until February 2001, when they gave permission for an expedition led by David Priddel.

Contrary to expectations, the team actually found a tiny remnant population on the rock, bringing the insect whose extirpation we directly caused out of extinction 80 years later (Priddel et al., 2003).

Initially, only three individuals – two adult females and one nymphal female – were found on a precipitous terrace at 65m elevation, on a shrub of the only host plant there, Melaleuca howeana. Another expedition in 2002 discovered 24 individuals dispersed in the same location; of the ten sexed individuals, eight were female.

What happened afterwards is a remarkably success of modern conservation biology, combining fieldwork to understand the insect’s biology, a breeding program in Melbourne Zoo’s Butterfly House that started from one adult pairs and now has thousands of insects, and public education that has made the Lord Howe stick insect a flagship species recognisable to all Australians. Not many insect species have nicknames. You can read all the details about this conservation campaign in Honan (2008).

Anyway, the conservation story isn’t why I am writing this post. A reader wrote in asking about the meaning of “land lobsters” and “tree lobsters”. These are common nicknames for Dryococelus australis, the Lord Howe stick insect, but the reader saw it in reference to another species, Eurycantha horrida.

In fact, “tree lobsters” and “land lobsters” are vernacular names for a specific ecomorph of stick insect, recognised for a long time (e.g. Gurney (1947)). Their generalised characteristics are:

  • Flightless;
  • Flattened body;
  • Robust rather than slender;
  • Highly sexually dimorphic: females have a long ovipositor, and males have very strong hind legs.
Phylogeny of "tree lobsters". Source: Buckley et al. (2009)
Phylogeny of “tree lobsters”. Source: Buckley et al. (2009)

A study by Buckley et al. (2009) conclusively showed that this tree/land lobster habitus holds no phylogenetic meaning. The red branches in their tree, above, show species that were traditionally put together in an “Eurycanthinae” subfamily. While not all Eurycanthinae were tree lobster-like, a lot of them were.

The fact is that the tree lobsters do not end up clustering together as any sort of subfamily, except perhaps in the Trapezaris – Canachus group, and so they are not related to each other. This demolishment of the subfamily came as a slight surprise at the time – the Eurycanthinae, with their restrained biogeography (Guinea to New Caledonia to Oceania) and characteristic tree lobster-like morphology as a special characteristic, have been recognised since the erection of the subfamily by  Brunner von Wattenwyl in 1893. You can even find comprehensive key to species (Zompro, 2001).

Instead, the evolution of this body type occurred multiple times independently. The authors speculate that similar evolutionary pressures led to this: the females all have a long secondary ovipositor to deposit their eggs inside soil; the males use their hind legs as an escape mechanism (not very useful against rats, obviously); the flattened body is very useful for hiding in crevices and other tight spots, just like with cockroaches. Such changes could have occurred with the convergent move to a surface-dwelling lifestyle.

Confusion over such vernacular names is the reason why proper scientific names were invented. What’s a daddy-long-legs? Is it a fly? Is it a pholcid? Is it an opilionid? Who knows? Vernacular names should be phased out of the scientific literature, especially when the species concerned are insects that are not easily distinguishable.

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