A vagrant timeline

In early March 2023, reports started coming in of vagrant emperor dragonflies spotted along the coast of southern Spain. Now, a month later, they have arrived to the UK!

Vagrant empress (Hemianax ephippiger) by Will Hawkes

There are several interesting questions to answer about this current influx of migrant vagrant emperors. For example: Where are they coming from? Are they relying on winds to spread through Europe? Are there several migratory routes from thier origin into Europe or several origins? It is possible that the influx seen are individuals that emerged from ponds as far away as the Sahel.

Looking at observations reported in to the French citizen science platform Faune France, the progression of the migration can be visualized (see accumulation of observations between March 16th to April 19th by week below).

Progression of observations of vagrant emperors through France (Faune France, www.faune-france.org)

The maps only show reports in France, and thus, it is difficult to know which routes the dragonflies might have taken prior to first being seen in southern France in mid-March.

It is possible that migratory vagrant emperors were flying in through France from the south and also along the northern coast of Spain. However, if one looks closely at the first and second progression maps, covering March 16th to March 23rd, the first observations in western France is from the middle of the country, not from the coast.

Suggested route of migrants, based on progression of reports to Faune France

This suggest that vagrant emperors observed in western France came from the south, and flew west and north-west through the country until they reached the western coastline. The maps above show a suggested spread of the dragonflies northwards through France.

On the maps the difference in altitude are shown in shades of grey, and the observations correspond with darker grey areas, i.e. valleys and lower altitudes. Thus, it appears as when the migrant dragonflies arrived to France from the south, they were split by the central mountain region, the ‘massif centrale’, and flew either west of it along the river Garonne, avoiding the Pyrenees to the south, or east of it, following the Rhône river valley, avoiding the Alps to the east.

Vagrant emperor migration through France, avoiding mountain regions

Since flying across France, there has been sightings of the dragonflies very recently in southern UK, from the Isles of Scilly to Cornwall (Poltesco) and Devon. One of the vagrant emperors that made it to the UK was found dead in a garden pond west of Plymouth April 14th, another one east of Plymouth April 12th.

When plotting the UK sightings (green) on a map together with all of the French sightings (yellow, orange, red), it appears as though the dragonflies started to cross the English channel when they reached the Cherbourg Peninsula:

Observations of vagrant emperors in France (yellow, orange, red) and the UK (green)

Whether crossing the English channel was promted by favourable winds or an inherant behaviour in the dragonflies, ushering them to migrate northwards, is unknown.

It will be very interesting to see how this migratory influx develops, and if the dragonflies continue to press north through the UK and the rest of Europe, and where the northernmost observation will be.