Marsh Fritillary Project Update

Earlier this year, INCC took a huge step toward securing the future of a fragile marsh fritillary butterfly population in South Wales.

In February, staff and volunteers collected 80 caterpillars from the wild to start Wales’ first marsh fritillary captive rearing programme. Between 10 and 20 wild caterpillars were taken from five donor sites in Rhondda Cynon Taff and Caerphilly.

The caterpillars were then taken to rearing pens at their new homes, including at the National Botanic Garden of Wales (NBGW). Different sites are used for rearing so that the overall risk to the caterpillars and project can be reduced.

In March, the project came across its first major hurdle. Parasitoid wasps Cotesia melitaearum were discovered in the rearing pens. The wasp is likely to be even rarer in Wales than the marsh fritillary. This is because the butterfly is the wasps only host species in Wales. Although harmful to the caterpillars and the project, the presence of the parasitoid wasp is a sign that the marsh fritillary populations at the donor sites is robust enough to support the two species.

The adult wasp first lays its egg in a marsh fritillary caterpillar in the autumn. The egg hatches and the larva slowly eats away at the caterpillar from the inside, leaving the caterpillars’ vital organs until last. In March, the wasp larva burst through the caterpillar and starts to create a silk woven cocoon, where it eventually transforms into an adult to start the process all over again. Once discovered in the rearing pens, the wasp cocoons were moved and released back to the donor sites.

The marsh fritillary caterpillars fed on a diet of devil’s-bit scabious and honeysuckle up until the middle of April when they started to pupate. Marsh fritillary pupa are small, beautifully patterned pupa and well camouflaged to blend into their marshy grassland habitat.

In just a few short months the caterpillars and pupa have experienced drought, sub-zero temperatures, parasitoid wasps and gale force winds. But, on the 7th May 2021, we had our first adult butterfly emerge from its chrysalis.

Its only the start of the project and the future will involve a lot more rearing, habitat restoration, research and monitoring. INCC has been lucky with all its support for the project, not least from our Student Placement, Katie Ritchie who is based at the NBGW. Katie has been responsible for looking after the caterpillars and ensuring that they are safe and have enough devil’s-bit scabious. Student Placement Blog: Katie Ritchie – Initiative for Nature Conservation Cymru.

To help with the future delivery of the project, INCC has employed a part-time Species Officer, Vaughn Matthews. Vaughn will be helping with the captive rearing process as well as developing research and working with partners to help restore marshy grassland habitat in the landscape.

There is still lots to do over the coming months and years to help safeguard the marsh fritillary in South Wales. Thank you for all the support and we look forward to providing you with more updates along the way.