Key Findings
My research revealed that three main habitat factors significantly influence where marsh fritillary butterflies thrive: ground temperature, bush cover, and ground moisture. Additionally, precipitation strongly correlates with larval nest abundance, highlighting how climate affects different life stages of this vulnerable species.
Population Dynamics Between Life Stages
One surprising finding was that counting larval nests in fall doesn’t reliably predict how many adult butterflies will emerge the following summer. This contradicts some previous studies but aligns with research showing high winter mortality among larvae. The harsh winter conditions and the larvae’s limited ability to move to better locations likely explain why initial nest counts don’t translate directly to adult numbers.
However, the reverse relationship proved much stronger: higher adult populations in summer consistently led to more larval nests in fall. This makes intuitive sense, as more breeding adults naturally produce more offspring, and this relationship is measured over just a few months rather than across the challenging winter period
Climate Impacts on Different Life Stages
Summer Precipitation Effects
Precipitation during summer months significantly boosted larval nest abundance but had no apparent effect on adult butterfly populations. This difference reflects the distinct needs of each life stage:
Larvae depend entirely on their host plant (Devil’s-bit scabious) for both food and shelter, and precipitation increases both the abundance and size of these plants
Adults have more flexible diets, feeding on various nectar sources like Bloody cranes-bill, Common blue daisy, and Tormentil
This flexibility likely evolved because the host plant doesn’t flower during the butterfly’s May-June flight period. The 2018 drought in Sweden dramatically illustrated this connection, when extremely low precipitation caused a 60% loss of host plants across the landscape, leading to significant population declines.
Habitat Preferences Across Life Stages
Ground Temperature: The Critical Factor
Peak ground temperature was the strongest predictor of habitat use for both larvae and adults, though adults showed greater sensitivity:
Adults: 54.8% increase in abundance per 1°C temperature rise
Larvae: 28% increase in abundance per 1°C temperature rise
For adults, adequate warmth is essential for flight, feeding, and reproduction. For larvae, warmer conditions accelerate development and improve survival rates from egg to larval stage.
Bush Cover: Finding the Right Balance
Both life stages benefited from moderate bush cover:
Adults: 4.1% increase per unit of bush cover
Larvae: 2.4% increase per unit of bush cover
This vegetation provides adults with necessary shelter while maintaining enough open space for basking and host plant access. For larvae, moderate bush cover creates optimal microclimates for their host plants while ensuring females can locate suitable egg-laying sites.
Previous research confirms that extreme vegetation heights are problematic: areas too open leave host plants isolated and vulnerable, while areas too dense make host plants difficult to find and reduce sunlight access.
Ground Moisture: Moderate Levels Preferred
Ground moisture had moderate effects on spatial distribution, with slightly stronger impacts on larvae. This connects to the precipitation-host plant relationship, as optimal moisture levels support healthy host plant populations without encouraging competing vegetation that might outcompete the butterflies’ preferred plants.
Conservation Implications
Habitat Management Strategies
- Maintain diverse vegetation structure with moderate bush cover
- Prevent excessive woody encroachment through appropriate grazing or cutting
- Preserve open areas that allow ground-level heating
- Consider microhabitat conditions rather than just broad landscape features