Marsh Fritillary Project Update December 2023

It’s over a year since our last update on the Marsh Fritillary population reinforcement project and a lot has happened since then, both on Llantrisant Common and in the rearing pens at the National Botanic Gardens. In the last update we were just about to embark on the release of the next batches of caterpillars on the common. INCC staff and volunteers carefully collected caterpillars from the Devil’s-bit Scabious plants in the rearing pens and transferred them to small pens ready for transport to the Common.

The reinforcement project is part of a wider landscape strategy aimed at getting more areas of habitat in the wider countryside into good condition for Marsh Fritillaries and other species.

Part of this strategy is to get suitable management onto areas of marshy grassland (ideally cattle grazing). The aim of this is to get the structure of the habitat right (not too long, not too short) but in some cases the sites need a helping hand if they don’t have good numbers of Devil’s-bit Scabious.

One such site in Rhondda Cynon Taff was visited in late 2022 with staff and students from Bridgend College. We planted out hundreds of Scabious plug plants in the hope that they would establish and start to make the site habitable for Marsh Fritillaries. We visited it again in late summer 2023 to find the Scabious doing well and the habitat structure improving too.

Ellyn collecting caterpillars from rearing pen.

Thermal image of basking caterpillars.

Late autumn and winter is traditionally a quiet period for the project as the caterpillars have entered hibernation both in the rearing pens and out on the common. They create a dense web down low in tussocky vegetation (or in the provided hay in the rearing pens) and stay there until the first sunny days of early spring.

Caterpillars will emerge to bask early in the next year – usually around late February/early March but if the sun is strong enough, they will emerge earlier to bask on vegetation. This year the first ones we saw in the rearing pens were at the end of January and we began to see more and more in the pens and then on the Common in the next few weeks.

More of these caterpillars were released through the spring as we wanted to empty the pens in order to remove the risk of the remaining individuals becoming inbred. They were placed in areas of good habitat that hadn’t had any caterpillars released in them to date.

Marsh Fritillary caterpillars in spring.

As the summer progressed INCC staff and volunteers visited the Common regularly to monitor the distribution of the butterflies. It’s still a thrill to see the fledgling population spreading slowly across the Common.

Volunteers releasing caterpillars at Llantrisant Common.

The final caterpillars were released in July 2023, shortly after this, Carys Romney, along with children from the local primary school began collecting Scabious seeds from nearby sites, as last year. These seeds have been taken to Bridgend College to be grown on in their Horticulture department, with students using different growing conditions to assess the best ways to optimise the amount of Scabious. This will again be used to populate the rearing pens as well as enhancing marshy grassland habitat in the area.

Schoolchildren collecting Scabious seeds.

Scabious seedlings flourishing at Bridgend College.

Larval web surveys were undertaken in early September to see how well they were doing and how far they had spread. Again we had over 100 larval webs, slightly down on the previous year but still a great result; the weather has led to a poor year for insects generally.

Marsh Fritillary larval web at Llantrisant Common.

Larval webs found at Llantrisant Common in 2023.

At the time of writing (December 2023) INCC are currently putting in a licence application to collect another cohort of caterpillars for the next couple of years’ captive breeding. If successful, we’ll be assessing which sites have populations resilient enough to allow collection of a small number of caterpillars in March 2024.

Again, without the support of funders, volunteers, project partners and local schoolchildren and college students we wouldn’t have been able to get to this point, so thank you for your continued support.

2 thoughts on “Marsh Fritillary Project Update December 2023

  1. This is a truly inspirational and heartening project. We are currently trying to improve habitat at West Cross Common (Gower Peninsula) to make the site more favourable for Marsh Fritillaries. I am planning on growing devils bit scabious on my allotment from locally collected seed, to increase numbers of the flower on the common. I will be interested to find out the most successful method of raising new plants from seed

    1. Hi Laura,
      Thanks very much for your kind words. Great to hear about your project at West Cross too. We’ve found DBS pretty easy to grow to be honest. We tend to sow it relatively densely in peat-free compost initially. We keep them in a polytunnel and then prick out the seedlings once they start to look cramped. Once they’re a bit stronger we either grow them outside or inside (I’m not sure which is best but probably outside so that they get used to real conditions) in trays, then eventually pots as they start to get a bit bigger. Keeping them from drying out at any point is one of the key things (unsurprisingly!). We usually then plant them out as small plug plants. I hope that helps – let us know if you have any issues or if you’d like to visit our polytunnel in the Amman Valley – you could have a chat with our volunteer that does most of the rearing. Best wishes, Vaughn

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