Migrant species
The remaining species on the Essex list are found only as a result of immigrations from abroad.
They may breed here in most years but cannot survive as resident species. The red admiral and pain-
ted lady breed in most years but the clouded yellows appear in numbers only infrequently. The other
migrant species are no more than rare and unusual vagrants. Fears had been expressed that habitat
changes abroad had ended for ever the massive immigrations of the regular migrants such as occurred
in 1949. The influx of huge numbers of these three species in the hot summer of 1983 suggests that
favourable climatic conditions are more important than the habitat changes. But the occassional
'good' year for migrant butterflies should not hide the fact that very large numbers of our resident
species have declined dramatically and Essex has an even more impoverished fauna than at any time
in the past.
Recolonisations and reintroductions
The recolonisation by the speckled wood has already been described. No other species lost to
Essex has yet recolonised as a breeding species except by deliberate reintroduction. The recent scat-
tered sightings of adults of the wood white and all the violet-feeding fritillaries (except the small pearl-
bordered) suggest that a natural recolonisation by some of these species may be a possibility if the
increasing frequency of coppicing makes Essex woods suitable for them. The sightings are concen-
trated in summers which were 'good' butterfly years for many species: implying that they arrived here
naturally rather than by release of captive bred specimens.
The same cannot be said of the sighting of the purple emperor in Epping Forest. A specimen
released by one of the many lepidopterists in the London area seems a more probable explanation than
immigration from a distant colony or the undetected survival of a colony since Victorian times.
The very recent detection of the brown hairstreak as a breeding species in Epping Forest is another
mystery. Undetected survival of a colony is certainly possible with such secretive species as
hairstreaks. On the other hand, deliberate introductions, in other counties, of the ecologically similar
black hairstreak have been very successful (Heath et al). So an unrecorded successful introduction
may explain the Epping Forest brown hairstreaks.
The only case where it is known that introductions enabled the species to recolonise Essex is the
heath fritillary. It was introduced into woods in the Southend area in the 1920s and 1930s and
survived as a breeding species until the early 1970s. Now a second phase of reintroduction is under-
way in another wood (an Essex Naturalists' Trust reserve) where its larval foodplant is still abundant.
Adults reintroduced in 1984 produced a generation of butterflies in 1985 - so the first phase of the
reintroduction has succeeded.
Of the many explanations put forward for the decline in butterflies, the fragmentation of suitable
habitats and their separation by wide tracts of unsuitable farmland habitats, seems likely to be a major
factor for those species which tend to exist as localised colonies and not to disperse widely in the adult
state (Heath et al.). Whereas, in the past, chance local extinctions could be made good by species
dispersing along hedgerows from nearby colonies, this cannot occur when the remaining colonies are
few and far between. In these cases deliberate reintroductions may be the only way of ensuring the
survival of the species. The introductions may need to be repeated if local extinctions recur: the rein-
troductions would be judged successful if the species established itself and increased for a few years
even if it then declined again. Experiments outside Essex suggest that the following species, at least,
are easy to reintroduce to suitable habitats: silver-studded blue, marbled white, marsh fritillary and
wood white. It is my view that the conservation bodies in Essex would do well to extend their carefully
monitored reintroductions to these species and also, perhaps, to some of the violet-feeding fritillaries.
Not only might such experiments increase the diversity of resident species in Essex but the experi-
ments could go a long way to answering the riddles as to why these species declined in the first
place.
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