Amphibious caterpillars in Hawaii

The Hawaiian Islands are renowned for their unique biota that display a number of bizarre adaptations that do not appear elsewhere in the world. Widely known examples of these include the predacious caterpillars in the genus Eupithecia, and the wekiu bug (Nysius wekiuicola) that lives on Mauna Kea eating insects that are blown to them on the wind.

Recent work by Daniel Rubinoff and Patrick Schmitz have added another example to the list: amphibious caterpillars. In a paper published in March in PNAS they describe the ecology of some recently discovered 12 currently undescribed species of the moth genus Hyposmocoma that are able to develop equally well both in and out of water. Intriguingly, a phylogenetic tree hypothesizing the evolution of these insects suggest that this amphibious trait arose independently at least four times, an unexpected result for a specialised trait such as amphibiousness.

The major driving force for the development of this unique lifestyle in Hawaii is believed to be due primarily to a lack of competition. Hawaii lacks the major aquatic insect orders of the stoneflies, mayflies and caddisflies (the latter two represented by introduced species only), leaving Hawaii's freshwater environments unexploited. Hyposmocoma has stepped into the breech.

In addition to the written paper, the authors have provided movies showing the caterpillars moving in and out of the water. They are provided as supplementary information to the paper and available on the PNAS website here and here. Unfortunately, a David Attenborough documentary this isn't. There is no informative commentary spoken with a British accent, but it is an interesting watch nonetheless.

References:
Rubinoff D, Schmitz P. 2010. Multiple aquatic invasions by an endemic, terrestrial Hawaiian moth radiation. Proceedings of the National Academy of Sciences of the United States of America 107(13):5903-5906

Zimmerman EC. 1957. Insects of Hawaii. Volume 6, Ephemeroptera-Neuroptera-Trichoptera and Supplement to Volumes 1 to 5. University of Hawai'i Press.

Fauna Hawaiiensis

I've always been surprised how hard it's been to find information on the beetles of Hawaii. Due to it being a state of the USA and the fascination for many other aspects of the fauna and flora of the islands I would've thought that it would be very easy to find out pretty much anything about the beetles of the area. This expectation for the most part has not been met.

Lately though, I've been having more luck. The other day I found the Proceedings of the Hawaiian Entomological Society, and today I found the website of Karl Magnacca. He's working on the Drosophila of Hawaii which form a very famous radiation with approximately 600 species found in Hawaii. A big task. He's also taken a number of photos of Hawaiian beetles, and has put online the masterpiece of early Hawaiian biological study: Fauna Hawaiiensis. This ambitious project details the entirety of the animals from Hawaii at that time. Vertebrates, insects, worms, springtails, molluscs: it's all here.

Melicope: Hawaii's export to the Pacific

Over the years, the general consensus has been that islands of the Pacific, and particularly the incredibly isolated archipelago we fondly know as Hawaii have been the passive collectors of fauna and flora that have just happened to have swum, flown, drifted, or been blown onto their fair shores. It's generally been thought to have been a one-way process, that once something has arrived there, it settles down and makes the most of their tropical paradise. Something that those of us stuck in cold climates can relate to very well -- why would you want to leave a place that is extremely amiable and is yours for the taking?

However, recent systematic research on a number of organisms is starting to shake up this tidy story somewhat. It appears that we may have underestimated the ability of these islands to send their biota elsewhere.

The particular paper sparking this post, written by Danica Harbaugh and coauthors, features the shrub Melicope. It's widely distributed across Asia and the South Pacific, but has undergone an "explosive radiation" in Hawaii, with 47 species found in the group. As usual, the authors hypothesised that all Hawaiian species had originated from a single colonisation and formed a monophyletic group restricted to the islands. Data from a number of genes were analysed, and it was found that although it does seem to be the case that all Hawaiian Melicope were derived from a single colonisation, it hasn't remained stuck in the one place. Surprisingly, their data suggested that Hawaii has exported some of their plants to the Marquesas Islands, where they have subsequently speciated.

This data adds to the body of work that suggests that Pacific biogeography is a lot more dynamic and complicated than initially suspected. It is also another example of the very intriguing connection that exists between Hawaii and the Marquesas.

References:
Harbaugh DT, Wagner EI, Allan GJ, Zimmer EA. 2009. The Hawaiian Archipleago is a stepping stone for dispersal in the Pacific: an example from the plant genus Melicope (Rutaceae). Journal of Biogeography 36: 230-241.

Belligerent newcomers and shrinking wings - Carabid Ecology on Maui

To make use of an allusion from literature, things are rotten in the Hawaiian Islands. Like many places, they are being overrun by Argentine ant (Linepithema humile) (Hymenoptera: Formicidae). Coupled with this, they also have a carabid beetle, Trechus obtusus that is running amok over the island of Maui. Stuck in the middle are a number of endemic carabids in the genus Mecyclothorax.

James Liebherr and Paul Krushelnycky have published a paper detailing the plight of the Mecyclothorax over the past seven years, and it makes for interesting reading. In a nutshell: Trechus obtusus was first found on the island of Maui in 1999 (sounds familiar…) and increased dramatically, such that a 4m2 collection of leaf litter in 2001 had 77 beetles in it. The numbers of Mecyclothorax since that time have had a statistically significant decline since then, while T. obtusus numbers remain approximately the same. The presence of ants is also an important predictor in whether or not Mecyclothorax is present in an area or not. The numbers of Mecyclothorax are significantly lower in ant-infested areas, while the abundance T. obtusus is not significantly affected by Argentine ants. It looks grim for Mecyclothorax, but the authors do not seem to express any pessimism about the future of the beetles.

Another interesting aspect about the system is how Trechus obtusus is losing its wings. T. obtusus has two forms - a fully winged (macropterous) form that can fly around, and a short winged (brachypterous) form whose wings reach halfway down the abdomen and is flightless. There has been a very rapid change in the proportion of wing forms in populations of T. obtusus on Maui. In one site, 0% of beetles collected in 2001 had short wings. Four years later, in 2005 15% of beetles collected were brachypterous. At another site the proportions have increased from 0% brachyptery to 18% in three years. This change has a number of possible consequences. It is hoped that the decrease in numbers of flighted individuals will help prevent T. obtusus from spreading to other Hawaiian Islands. However, this does not prevent it from invading through human transportation, which is the most likely way it got to Maui in the first place. Second, the dimorphism of T. obtusus will no doubt help it spread around Maui to a much greater extent, and form more stable populations, than the endemic Mecyclothorax which are exclusively brachypterous.


Wing dimorphism is considered to be determined by a single allele. Individuals with full wings are thought to be homozygous recessive, while shorter wings can be heterozygous or homozygous dominant. While the authors suggest that all of the first beetles to arrive were macropterous (i.e. homozygous recessive), this would seem to indicate that there would be no alleles for brachyptery in the population. The situation here probably suggests that wing size in carabids is slightly more complicated than classical Mendelian genetics, and that more than one allele influences the size of wings in Trechus obtusus.

The influence of Argentine ant on the populations of carabid beetles is also pretty scary. Argentine ant is one of the world's worst invasive ant species and it is established in Hawaii, New Zealand and Australia. It is not found elsewhere in the Pacific. It is one of the species on the Pacific Ant Prevention Plan and it is hoped that it doesn't get established. The carabids elsewhere in the Pacific are not well known, and their response to Argentine ant invasion would probably be similar to the situation in Hawaii.


The globalisation of biodiversity has had a huge impact on native ecosystems. It looks set to continue, despite advances in biosecurity policy and techniques. It looks gloomy, and to an extent it is. However, nature has survived this long, and will continue to get by, though in a slightly more impoverished state. Another aspect of invasions that I haven't looked up yet is the beneficial side, where new organisms enrich and add to the indigenous ecosystem. Does it happen? I don't know, and it's not something you hear about. Maybe an idea for someone?

Liebherr, JK; Krushelnycky PD. 2007.
Unfortunate encounters? Novel interactions of native Mecyclothorax, alien Trechus obtusus (Coleoptera: Carabidae), and Argentine ant (Linepithema humile, Hymenoptera: Formicidae) acress a Hawaiian landscape.
Journal of Insect Conservation 11:61-73