Adonis Blue notes from the Shoreham area, Sussex

[Perseus]

Hello,

Adonis Blue
Polyommatus bellargus

The sole foodplant is Horseshoe Vetch (Hippocrepis comosa).
Eggs are laid singly, typically on the underside of terminal leaves of the
foodplant. A preference is shown for small sprigs of foodplant growing in
the turf, rather than large masses of foodplant.
http://www.glaucus.org.uk/Hippocrepis_comosa.html

The requirements of this butterfly are different from the Chalkhill Blue. It
favours a greater variety of Horseshoe Vetch and will lay eggs on plants
eschewed by Chalkhill Blues.

Adur Observations:

The Adonis Blue is very frequent on the Mill Hill lower slopes in both two
broods and is widespread over the downs where its food plant is available.
It is occasional on part of the Lancing Ring meadows (where the land has not been disturbed for 100 years), occasional to frequent on the Anchor Bottom pastures (thought to be vagrants from Beeding Cement Works area in part), occasional to frequent on the verges of the path leading to Southwick Hill from north Southwick, occasional on the Slonk Hill Cutting (road embankment), north Shoreham.

Local History: this butterfly has shown a dramatic post-WWII decline on the Anchor Bottom pastures where it was previously abundant. Agricultural improvement of fertilising the chalkhill and encouraging grasses and elimination of toxic (to livestock) Horseshoe Vetch is thought to be the reason.
It seems to slowly colonise areas of Horseshoe Vetch whereas the Chalkhill Blue does not colonise in the last 35 years.

The book says Adonis Blue colonises short sward. This matches observations locally, but the reason is just as likely as anything to be because Horseshoe Vetch (the food plant) is able to maintain populations in short sward grasslands better than in meadows. However, near Southwick Hill it is found amongst the long grasses on the verges. It does not seem so reliant as the Chalkhill Blue on long grasses for night roosting, but this is just surmise.

On Anchor Bottom the Horseshoe Vetch is so exiguous that no attributes to the appearance of the Adonis Blue with cattle grazing can be concluded. Rather the opposite as cattle destroy Horseshoe Vetch. It is just that Adonis Blues have a greater aptitude for using isolated clumps of Horseshoe Vetch than Chalkhill Blues and they can survive better the inroads of grazing. Horseshoe Vetch survives under low density sheep grazing and changing from sheep to cattle is contra-indicated. It is an open question whether sheep confer advantages over non-grazing on low fertility slopes where the sward remains constantly low and where grasses are not the dominate flora (e.g. Mill Hill lower slopes where the dominant flora is Horseshoe Vetch and other herbs.)

On Horseshoe Vetch land the object is prevent the incursion of scrub.
Livestock fail to make any inroads into this and the scrub has to be removed by Man. On pastures, scrub is removed for various reasons, and this factor alone is responsible for the Adonis Blue Butterfly surviving on pastures.

The Adonis Blue is not a long sward meadow butterfly. Consequently it is absent from most of the Lancing Ring meadows. Its prime area is for low fertility natural chalkhill where the low fertility is responsible for the short sward (e.g. the lower slopes of Mill Hill).

Mill Hill 2007
http://www.glaucus.org.uk/MillHill2007.html
Shoreham Bank 2007
http://www.glaucus.org.uk/VetchTrail2007.htm

Cheers

Andy Horton
glaucus@hotmail.com
Adur Valley Nature Notes (including Shoreham-by-Sea, West Sussex)
http://www.glaucus.org.uk/Adur2005.html
http://www.glaucus.org.uk/Adur2006.html
http://www.glaucus.org.uk/Adur2007.html
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