Saturday, 4 March 2017

Spain 26: Butterflies

Clouded Yellow
By November the number of butterflies on the wing even in Spain. We saw very few most days, but on the trip down to the Ebro Delta we stopped for lunch in a warm spot where we caught up with a few late individuals:

Clouded Yellow Colias croceus
Although the Clouded Yellow is one of the most widespread yellow butterflies in Europe it is only a summer migrant in Britain, as the caterpillars seldom survive the winter. The larval foodplants are various clovers, alfalfa (lucerne) and other low growing members of the Fabaceae, with the adults preferring open flowers such as thistles and dandelions. They often migrate in vast numbers, and in some years they can be quite common in southern England. Arriving around May, they produce one or two generations and in the autumn there may be a reverse migration down to the Mediterranean.

Bergers Clouded Yellow Colias alcafariensis
Berger's Clouded Yellow
This species is a very rare immigrant to Britain, as it is almost entirely resident in its home range of southern and central Europe. It is also somewhat more of a specialist than C.croceus, with the larvae feeding only either on Horseshoe Vetch Hipppocrepis comosa or Crown Vetch Coronilla varia. Even though it reaches northern France as a resident, it appears that it cannot survive the damp of a British winter (it hibernates as a small larva), which explains its absence from the British resident butterfly fauna.

Mazarine Blue Cyaniris semiargus
Mazarine Blue
Sadly, this species is now extinct in the UK, with the last know colony dying out in 1877. The caterpillars feed on clover, which is still widely sown as a fodder crop, but it appears that changing in farming practises or climate, or both, resulted in their extinction. As with other blues, they undoubtedly have a close relationship with ants, but this has been little studied. The larva feeds on the flower heads of Red Clover and hibernates as a young larva. In the south there are several broods each year, with only a single brood in the north of its range or at high altitudes.

Silver-Studded Blue Plebejus argus
Silver-Studded Blue
In the UK this is a declining species with scattered colonies in north Wales and along southern England, especially on lowland heath and coastal dunes. They can use a variety of foodplants for their larvae, including heather, gorse, Common Birds-Foot Trefoil. They overwinter as eggs, with a single brood of adults appearing in July. An important factor in this species ecology is their relationship with black ants – Lasius niger in damp areas and L. alienus in dry areas. The adult female butterfly actively seeks out the ant nests and lays her eggs close to them. When they hatch the caterpillars are immediately picked up by a worker ant and carried to their nest. What happens there is not clear, but they may feed on the roots of plants growing through the nest. As they grow the ants carry them from the outer chambers of the nest to their food plants where they feed at night. The ants do all this in return for sugar secretions produced by the larvae, which also probably produce a range of appeasement compounds to encourage the attendance of the workers. Even when they pupate the ants continue to guard the chrysalis, and when the adults emerge the still-damp adults retain their attractiveness as they climb up grass stems to expand and dry their wings.

Long-Tailed Blue Lampides boeticus
Long-Tailed Blue
We found only a single worn individual of this very widespread and migratory species, which has increasingly reached the UK in recent years. The caterpillars feed inside the seedpods of various Fabaceae, and in Britain often arrive inside imported peas and the like. In southern Europe they seem to use Cytisus or other shrubby plants.

This concludes my survey of the various birds and other wildlife we saw in just a single week in November in north west Spain – I hope readers have enjoyed it.

(images from Wikipedia, Clouded Yellow, Silver-Studded Blue pics my own)

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