Visit to Nat Hist Mus of London

Rhionaeschna bonariensis, a migrant from South America

The Natural History Museum of London holds some 80 million specimens of botany, zoology, mineralogy and paleontology. In the entomology department, the Insect Division, every curator is responsible for about 1 million or more specimen each. This means that the aim to digitise each and every specimen is a huge task.

Thus, when I asked if I could come to collect some wing samples of migratory species for isotopic analysis, I was told that it would be greatly appreciated if I could combine my work with the digitising work.

When digitising specimens for the museum, the information needed includes a unique number and QR barcode (picture below). QR stands for “quick response” and is a type of barcode that can be scanned and linked to information. With both a number and a QR code, each specimen can have its accompanying data quickly accessed. The picture below is of an exuvia from a downy emerald (Cordulia aenea) “holding” its barcode.

The Odonatas, dragonflies and damselflies, were kept in a collection room in the Darwin Centre of the museum. The room consisted of a long series of compact shelves that can be moved to create space between them using a whinch. On each shelf, there were several cupboards that could be locked and inside them, stacked on drawer rests, archaic looking, wooden trays with glass lids, about 50x70 cm in size.

On the wooden trays, protected under the glass lids, were the dragonfly specimen, pinned to the tray floor. On the pins underneath each specimen were little paper notes, indicating information on species, location, year, collector’s name, who had determined which species it was etc. Often though, very little information was given, and many details were missing. But sometimes, great snippets of history was preserved on those small pieces of papers, and it was absolutely amazing finding them.

Below is a vagrant emperor (Hemianax ephippiger), caught at Quetta (now a city in Pakistan). There is no year given and no information on who collected it, just a date: June 03. On the other hand, the collector has written down an observation made when the dragonfly was caught:

“This species was in thousands at Quetta June 03;

I never saw as many dragonflies anywhere”

Even though the Quetta-specimen did not have a date or a collector name, a second specimen, also caught in Quetta June 3rd had more notes pinned to it. On one of these it said “CG Nurse". Charles George Nurse was an English officer and naturalist stationed in India 1881-1915, and he collected around 3000 insects for the Natural History Museum in Quetta. As the date, species and location is the same, I think it is safe to assume that both these specimen were caught by CG Nurse. As he left India in 1915, they must have been collected before then.

Finding specimen, carefully collecting samples, writing down all the information and cutting out barcodes took quite some time. During my two and a half days at the museum I samples globe skimmers, vagrant emperors, migrant hawkers, four-spotted chasers and Aeshna bonariensis. But I did not have time to look at several more migrant species, so I am hoping to come back later in the autumn.

Aeshna bonariensis (now known as Rhionaeschna bonariensis) is only found in South America, where it aggregates in huge swarms that sweep in just before the Pampero wind. The Pampero occurs over the Pampas of Argentina and Uruguay and it marks the passage of a cold front, often bringing a considerable drop in temperature. In 1912 WH Hudson wrote down is experiences of these “dragonfly storms”:

Aeschna bonariensis Photo: Diego Trillo

“The most common species is the Aeschna bonariensis, the prevailing colour of which is pale blue.

…the really wonderful thing about them all alike is, that they appear only when flying before the southwest wind, called pampero -the wind that blows from the interior of the pampas. The pampero is a dry, cold wind, exceedingly violent. It bursts on the plains very suddenly, and usually lasts only a short time, sometimes not more than ten minutes; it comes irregularly, and at all seasons of the year, but is most frequent in the hot season, and after exceptionally sultry weather.

It is in summer and autumn that the large dragon-flies appear; not with the wind, but -and this is the most curious part of the matter- in advance of it; and in as much as these insects are not seen in the country at other times, and frequently appear in seasons of prolonged drought, when all the marshes and watercourses for many hundreds of miles are dry, they must of course traverse immense distances, flying before the wind at a speed of seventy or eighty miles an hour.

On some occasions they appear almost simultaneously with the wind, going by like a flash, and instantly disappearing from sight. You have scarcely time to see them before the wind strikes you. As a rule, however, they make their appearance from five to fifteen minutes before the wind strikes; and when they are in great numbers the air, to a height of ten or twelve feet above the surface of the ground, is all at once seen to be full of them, rushing past with extraordinary velocity in a north-easterly direction.

In very oppressive weather, and when the swiftly advancing pampero brings no moving mountains of mingled cloud and dust, and is consequently not expected, the sudden apparition of the dragon-fly is a most welcome one, for then an immediate burst of cold wind is confidently looked for. In the expressive vernacular of the gauchos the large dragon-fly is called “hijo del pampero” -son of the south-west wind“

/ William Henry Hudson, 1912, “The Naturalist in La Plata“

Unfortunately, the blue colour that Hudson described, and the beautiful contrast of black present on the abdomen of this species (distinctive of most Aeshnas) disappears when the dragonfly has been dried (as on the picture below). This loss of bright colour is probably one of the reasons why naturalist and people in general, are less interested in collecting dragonflies.