Southern Migrant Hawker (Aeshna affinis) Exuviae Study

I was very fortunate in June when visiting the Southern Migrant Hawker colony at Canvey Island, Essex, to see a few newly emerged individuals still with their exuviae. I was really hoping on this visit to be able to find and collect a few of these exuviae and I was not to be disappointed as I collected 15 exuviae to add to my growing collection. Quite a few others were seen clinging to the reeds throughout my visit. As with all the exuviae I often find, its always nice to know the key features for them but not that much information is out there to identify this species so far but a study by David Chelmick in 2011 published in the Atropos Journal provided an interesting insight into some of the key features required to identify this species exuviae.

 

Southern Migrant Hawker Exuviae (Aeshna affinis) - female

Southern Migrant Hawker Exuviae (Aeshna affinis) - female

 

I have therefore spent a few hours myself using this information to acquaint myself with the features which on inspection, can be quite easily recognised. I will at a later date do a comparison with the very similar exuviae of the Migrant Hawker (Aeshna mixta) to show the similar features. Having read the paper by David Chelmick, the key features noted at this time were the length of the mask and lateral abdominal spines along with the length of the ovipositor in the female and the overall dark appearance of the exuviae. The mask in the Southern Migrant exuviae is quite squarish in shape compared to the longer mask of the Migrant Hawker which was evident on my specimens in my collection but the length was most notable with the Southern Migrant Hawker mask viewed from underneath reaching between the first and second pairs of legs compared to the Migrant Hawker exuviae which reaches beyond the second pair of legs.

 

Southern Migrant Hawker Exuviae (Aeshna affinis) - female showing the mask

Southern Migrant Hawker Exuviae (Aeshna affinis) - male showing the mask NOT reaching past the second pair of legs.

 

The lateral abdominal spines on segment 9 in the Southern Migrant Hawker are slightly shorter than those of the Migrant Hawker but this in some individuals, was quite hard to see although with a hand lens, it was able to not this subtle difference.

 

Southern Migrant Hawker Exuviae (Aeshna affinis) - female showing the proportionately shorter lateral abdominal spines on S9

 

A notable difference seen was the length of the female ovipositor which reaches nearly to the end of S10 whereas the ovipositor in the female Migrant Hawker does not reach beyond S9.

 

Southern Migrant Hawker Exuviae (Aeshna affinis) - female showing the ovipositor reaching at least halfway along S10

 

David also noted that the exuviae observed in 2011 were very dark compared to the lighter coloured Migrant Hawker exuviae. Looking at both species together in my collection would seem to back up this theory with most Southern Migrant Hawker exuviae appearing darker.

 

    Southern Migrant Hawker Exuviae (Aeshna affinis) - female

Southern Migrant Hawker Exuviae (Aeshna affinis) - male underside

 

Its been very interesting spending time studying the exuviae of this still very rare dragonfly in the UK and educating myself but hopefully after this year, there will be plenty more to be seen next year. As the dark evenings start to draw in and more time is spent inside, I will hopefully post a comparison of the Southern Migrant and Migrant Hawker exuviae soon as well as some of the other 'new' exuviae I have collected throughout the season.