Segment 1 — The Cold Open

Segment 2 — The Good Intention

The English race of the Large Copper, Lycaena dispar dispar, had disappeared by 1851 after centuries of fen drainage for agriculture. By the early twentieth century only fragments of wetland remained in eastern England. Capt. E.B. Purefoy, an experienced lepidopterist, decided that the newly discovered Dutch race Lycaena dispar batavus offered a chance to return the butterfly to one of those fragments. Woodwalton Fen, a small National Trust reserve in Huntingdonshire, still held pockets of suitable vegetation. Purefoy and the reserve managers believed that preparing the site with its larval foodplant would let a self-sustaining colony establish itself inside the protected boundary. The plan reflected the best available knowledge: the butterfly’s extinction had been caused by habitat loss, so targeted habitat restoration plus fresh stock should reverse it.

The fenland drainage that removed the original English population had begun in the seventeenth century with the cutting of large straight channels and the installation of wind-powered pumps. By the nineteenth century steam engines accelerated the lowering of water levels across hundreds of square miles, converting peat soils into arable fields. Purefoy therefore worked with a landscape whose hydrology had already been altered for more than two hundred years. He could see that the remaining fragments were small, yet he also knew that the Dutch race had evolved in similar, if not identical, wetland conditions. The decision to proceed rested on the assumption that a carefully chosen reserve could be made sufficient if the missing plant was restored.

Segment 3 — The Implementation

In 1927 Purefoy released twenty-five males and thirteen females of the Dutch race at Woodwalton Fen after the reserve had been planted with great water dock. The following year more than one thousand adults were counted on the wing, a result that appeared to confirm the approach. Learn Butterflies records that the early numbers encouraged everyone involved. The reserve staff continued modest management, keeping the foodplant abundant inside the fen’s existing ditches and pools. No one at the time expected that the colony would require repeated human intervention simply to persist.

The planting itself involved setting out hundreds of young Rumex hydrolapathum plants along the wetter margins of the reserve’s internal waterways. Purefoy chose locations where the peat remained saturated for most of the year, matching the conditions he had observed in Dutch colonies. The 1928 count of over one thousand adults therefore represented roughly twenty-seven times the number of founders, an apparent multiplication that suggested the restored foodplant and the protected status of the fen were together sufficient. Wardens recorded the presence of eggs and larvae on the dock leaves that same season, reinforcing the sense that the cycle had closed.

Segment 4 — The Unintended Consequences

The land beyond Woodwalton Fen’s boundaries had been progressively drained for arable farming since the seventeenth century. Each new pump and ditch lowered the regional water table, pulling moisture out of the reserve through the peat. Great water dock, which needs consistently wet conditions, became harder to maintain in sufficient density. Duffey’s studies and the records kept at the reserve show that natural recruitment soon fell below replacement levels. Wardens responded by rearing butterflies in a greenhouse and releasing batches of adults each summer, a practice that continued for decades. Larvae were also caged on selected plants to protect them from flooding or drought. These measures kept a visible population alive, yet the colony never became independent of the annual supplements. By the late 1960s a major flood further damaged the foodplant stands, prompting another round of captive rearing after 1969. The surrounding agricultural drainage continued unchanged, so the hydrological deficit grew rather than shrank. The second- and third-order effects were cumulative: each year of lowered water table reduced the area of suitable dock, which in turn increased the proportion of the population that had to be artificially supported. Without that support the numbers would have collapsed far earlier than the early 1990s, when the last supplemented adults were seen.

The peat itself compounded the difficulty. Once drained from the outside, the organic soil began to oxidise and subside, lowering the surface of the reserve relative to the surrounding fields and making it even harder for water to remain at the level the dock required. Every additional pump installed on neighbouring farms increased the gradient, drawing water through the peat more rapidly. The wardens’ greenhouse rearing therefore addressed only the symptom—the shortage of adult butterflies—while the underlying shortage of suitable larval habitat continued to widen. Caging larvae protected individuals from immediate weather extremes, yet it could not expand the total area of dock that stayed wet long enough for the caterpillars to complete their development. The arithmetic of the intervention thus shifted year by year: more adults had to be reared to compensate for fewer naturally occurring plants.

Segment 5 — The Aftermath

After the final sightings in 1994 and 1995 the formal reintroduction programme at Woodwalton Fen ended. The site remained a National Nature Reserve, but managers accepted that a viable Large Copper population could not be sustained without restoring the wider fen hydrology. The Great Fen project, now under way, aims to re-wet large areas of former farmland between Woodwalton and Holme Fen, using clay bunds and controlled water levels to recreate the conditions the butterfly once required. No new releases have occurred while the landscape-scale work continues. The original 1927 effort therefore stands as a sixty-year demonstration that protecting a single fragment is not enough when the surrounding drainage regime remains unaltered.

The project’s current phase involves purchasing arable land and installing impermeable barriers so that winter rainfall can be retained rather than pumped away. These measures address the same water-table gradient that had steadily reduced the area of great water dock inside the original reserve. Until the restored blocks reach a sufficient size and wetness, however, any reintroduced butterflies would face the same constraints that forced the earlier programme into perpetual supplementation.

Segment 6 — The Lesson

Purefoy and the Woodwalton wardens treated the reserve boundary as the decisive limit of their intervention; the result was a population that existed only inside annual budgets for captive rearing. Any plan that sets a fixed geographical perimeter must also secure the water regime across that perimeter, or the foodplant itself will disappear. When the next reintroduction is considered, the test will be whether the Great Fen’s restored water table can support great water dock without constant human rescue. The same question faces every recovery project that begins inside a remnant habitat ringed by intensified land use.

Sources

• learnbutterflies.com — Large Copper
• dispar.org — dispar
• ukbutterflies.co.uk — Large Copper - Lycaena dispar
• archive.org — HISTORY OF ESTABLISHMENT ATTEMPTS WITH THE LARGE COPPER BUTTERFLY LYCAENA DISPAR (HAWORTH) (LEP.: LYCAENIDAE)
• sciencedirect.com — The re-establishment of the large copper butterfly Lycaena dispar batava obth. on Woodwalton Fen National Nature Reserve, Cambridgeshire, England, 1969–73
• conservationevidence.com — Re-establishment of the large copper butterfly Lycaena dispar batava on Woodwalton Fen National Nature Reserve, Cambridgeshire, England
• conservationevidence.com — Ecological studies on the large copper butterfly Lycaena dispar (Haw.) batavus (Obth.) at Woodwalton Fen National Nature Reserve, Huntingdonshire
• greatfen.org.uk — Woodwalton Fen

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