Family - PIERIDAE
subfamily - COLIADINAE
Beachy Head, East Sussex ©
In the early
days of English entomology the male of this beautiful insect was
known as the Saffron butterfly, and the female was called the
Spotted Saffron. The name Clouded Yellow was given to it in the 18th
century, and may well have been derived from the expression "cloud
of yellows", as the butterfly migrates to Britain in swarms, and has
often been reported as seen migrating across the English Channel as
a cloud of yellow over the sea. There is a famous account by Rev.
Harrison, who in 1868, at the age of 11 sat on a cliff near
Marazion, Cornwall, and observed "a yellow patch out at sea, which
as it came nearer showed itself to be composed of thousands of
Clouded Yellows, which approached flying close over the water,
rising and falling over every wave till they reached the cliffs,
when I was surrounded by clouds of Colias
( crocea ) which settled on every
Clouded Yellow is an abundant and widespread butterfly in North
Africa and the Mediterranean region, from where it migrates
north-wards each year.
Migrations usually follow the same route, starting in north Africa
and then heading north through Spain and France, with the bulk of
migrants entering Britain along the coast of Dorset. Smaller numbers
migrate across from Tunisia to Italy, then east around the Alps,
entering Britain via Kent, Essex and Suffolk.
Numbers arriving in
the UK vary from year to year. In some years no more than a couple
of dozen are recorded, but about once every decade
much larger numbers arrive, the most famous invasion occuring in
1947. Then, as quoted by CB Williams in his book Insect Migration, a
Mr Blake, aboard a ship in the English Channel in October of that
year, recorded that "for many miles he saw Clouded Yellows over the
sea". He estimated that "the flight was on a front of about 50
miles, and that there must have been well over a hundred thousand
butterflies taking part".
first wave of immigrants usually arrives in southern England in
early May and produces a new generation of butterflies that emerge
in July and August. These are often supplemented by a second wave of
immigrants - the progeny of butterflies that bred in France, which
may arrive at any time during the summer. In very warm summers there
may be a further UK-bred generation emerging in September, October
or even November. There is evidence that butterflies emerging in
central and northern England may sometimes undertake a return
female, Beachy Head, East Sussex ©
very mild winters e.g. 2006-2007 the Clouded Yellow can successfully
over-winter in the larval stage at certain sites along the coasts of
Dorset, Hampshire and the Isle of Wight. Consequently a small number
of adults may emerge as early as February. Normally however the
species perishes with the onset of winter.
Clouded Yellows of both sexes normally have deep
yellow uppersides with broad black margins, but the females have a
row of pale yellow spots within the margins. About 5% of females are
of a paler whitish ground colour. These are known as var.
helice, and are commonly mistaken for
females of the very much rarer Pale Clouded Yellow and Berger's
Clouded Yellow. In both of the latter species however the upperside
is a beautiful primrose yellow, and the hindwing borders are much
In Europe there are no less than 12
Colias species, several of which are
difficult to tell apart in the field. Identification is further
confused by the presence of sterile hybrids ( e.g.
erate x crocea
) in areas where the distribution range of the species overlaps.
The name crocea replaces the earlier
name croceus which is regarded as
The migratory nature of the Clouded Yellow means that it can be
encountered in almost any habitat. It penetrates well inland, and
can be found as far north as the Outer Hebrides. The highest numbers
however occur along the southern counties of England, particularly
in Devon, Dorset, East Sussex and on the Isle of Wight.
Hampshire generally receives fewer Clouded Yellows than these
counties, probably because many migrants are diverted around the
Isle of Wight coast to Dorset or Sussex.
male, Beachy Head, East Sussex ©
butterflies breed in a wide range of habitats including
cultivated lucerne fields, clover-rich farm headlands, steep
well-drained chalk and limestone grasslands, abandoned quarries,
road and rail embankments - anywhere in fact where the foodplants
grow in profusion in a warm dry habitat.
Colias crocea, freshly emerged male,
Beachy Head, East Sussex ©
butterfly is multi-brooded in warmer parts of it's
range, but in Britain it normally produces only a single generation,
emerging in July and August - the progeny of adults that migrated
northward from the continent in May or June. In particularly warm
summers there is often a partial 2nd brood that emerges in October.
These late emerging adults and any resulting eggs or caterpillars
normally perish in early winter, but at a couple of sites on the south
coast caterpillars occasionally overwinter successfully, producing a
few adults in February or March.
eggs are laid singly or occasionally in two's or three's, on the upper
surface of leaflets of red clover Trifolium
pratense, lucerne Medicago sativa,
horseshoe vetch Hippocrepis comosa,
bird's foot trefoil Lotus corniculatus,
sainfoin Onobrychis viciifolia, kidney
vetch Anthyllis vulneraria, or black
medick Medicago lupulina. They are pale
yellow at first, quickly turning to pink and finally to orange. They
hatch after about 7 - 10 days.
Clouded Yellow larvae are rough
textured, dark green in colour, with a pale yellow lateral stripe and
orange dashes between the spiracles. They feed diurnally on the leaves
of the foodplants.
hatching in May and June feed up and become fully grown within about 3
weeks but those of the 2nd brood feed very and usually perish with the
arrival of the first frosts in early November. In warmer regions of
Europe they continue to feed during the winter months, and do not
enter a state of diapause.
The pupae are yellowish green,
marked on the wing cases and abdomen with tiny black dots. They are
extremely difficult to find in the wild, attached by the cremaster and
a fine silk girdle to stems of the foodplants or other nearby plants.
The adults emerge after about 18 days.
male, Beachy Head, East Sussex ©
fly very rapidly and purposefully, migrating in
search of breeding sites, stopping for a day or two to refuel at
Once they discover a suitable area with
an abundance of the larval foodplants they tend to remain for several
Colias crocea, male at roost, Cissbury
Ring, West Sussex ©
On warm summer days they spend long
periods flying restlessly from flower to flower, nectaring at small
scabious, field scabious, devil's bit scabious, knapweeds, cat's ear,
stemless thistles, mouse-ear hawkweed, marjoram, clovers, trefoils and
When feeding they remain extremely alert,
and rarely settle for more than 3-4 seconds at a time. A minor and
temporary drop in temperature however is sufficient to invoke a
resting phase when they settle in rabbit scrapes or other depressions
where they may remain stationary for several minutes.
sunny mornings males
patrol back and forth over the breeding
sites, exhibiting a regular cycle of nectaring, resting and searching
for potential mates. Females are nearly always mated prior to their
maiden flight. I often find copulated pairs in which the females still
have limp wings and have clearly only just emerged. The butterflies
remain joined for about 1-2 hours during which time they usually
remain stationary, hidden among grasses. Nevertheless if disturbed
they readily take flight, with the male carrying the female. Normally
they resettle nearby among herbage, or on bushes, but I have known
them to fly up to land high in the tree tops.
Colias crocea ( female on right ), Beachy
Head, East Sussex ©
In October 2009 at Beachy
Head in Sussex I watched a male pounce on a freshly emerged resting
female. He danced around her, then landed behind her and tried to walk
into the gap between her almost-closed wings. She then outspread her
wings and raised her abdomen, which the male tried to pull down with
his forelegs. Within a couple of seconds he realised he was onto a
loser and flew off. The female then flapped her still-limp wings a
couple of times and then held them half open for another couple of
seconds. Then she closed her wings and remained stationary to complete
the wing drying process. I was very interested in the fact that she
rejected the male, even though she had clearly only just emerged. She
may possibly have already mated with another male, immediately after
emergence. Alternatively she may simply have not been ready to accept
the male's advances until wing drying was complete.
Clouded Yellow, female rejecting male by raising abdomen to prevent
late afternoon both sexes seek roosting sites. Sometimes they spend
the night beneath bramble leaves or other foliage, but normally they
tuck themselves away among grasses. If a large number of Clouded
Yellows are present at a site, they often roost in pairs, or even in
Colias crocea at roost, Beachy Head, East