Australian Museum entomologist Dr Chris Reid shares a story of painting rare beetles.
Many of the world’s rarest species are known to be so rare because their entire populations are easily mapped out. For example, on small islands, where the thing occurs nowhere else and it’s easy for an observer to walk around recording specimens. I’m thinking plants, e.g. the coco de mer of the Seychelle Islands, which is a 30m palm tree with the largest seed in the world, or the Komodo dragon of eastern Indonesia, which is 3m long and stands out like a sore thumb in the Flores savannah (presumably observers there are a little cautious).
It’s a little harder with insects. On Lord Howe Island there was once a large black beetle, Promethis sterrha, flightless and feeding at night on green algae on tree trunks. The larva fed on rotting wood. The beetle was collected on the island until 1916. Then rats arrived through the stranding of a supply ship in 1918 and in 10 to 20 years a whole load of different animals went extinct, including several birds and several insects. And Promethis was not seen again on the main island.
However, Lord Howe Island has many small satellite islets or islands or just rocks. Some are large enough to support vegetation and one of these is Blackburn Island, about 300 x 100m of vegetated rock in the middle of the coral reef.
Promethis sterrha was discovered on Blackburn Island in 2001. Because of the small size of the island plus the fact that the species is associated with trees and there are only 14 trees, Promethis sterrha has been listed as critically endangered under NSW government legislation. When a species is listed in that category it becomes the target of research to find out as much about it that will help in developing a recovery program.
Thus I found myself preparing to visit Blackburn to individually mark beetles for ‘mark and recapture’. The method is simple – find a permanent marking technique, which doesn’t have an impact on the health of the beetle, mark everything found on a night, then go out again and try to find the marked specimens, comparing them with the unmarked.
We wanted to know: How many adults were there? How long did they live? Did they move much between trees? But what should I use for marking? I thought paint would be too slow to dry so I consulted with various women colleagues about nail varnish and did some experiments on wing cases of beetles pinned out in the garden.
We have now done this on two trips, with interesting results. The total adult population is 240-400, we recovered several on the second trip with markings that were six months old, and they are generally faithful to trees, even over a six-month period.
I am extremely grateful to those colleagues who sacrificed their nail varnish in the name of science.
