Who visits forest bramble flowers, and when? What camera traps reveal about pollinators in the woods

A bumblebee on a bramble flower

by Bonneau-Chloup et al.

Forest understories are the scene of everyday interactions between plants and insects, yet we know surprisingly little about who visits forest flowers, when they do it, and if they are sensitive to the very local microclimate. Most pollinator research focuses on open meadows or crops, leaving forest flower-visitor communities largely overlooked, even though forests host some specialized insects and may represent a refuge for more generalist wild pollinators in increasingly farmed or urbanised landscapes.

To fill this gap, we set up a non-invasive video monitoring system on bramble flowers (Rubus fruticosus agg., a common forest-edge shrub) across four patches of the Fontainebleau forest, near Paris. Over 369 hours of footage, we recorded every insect that visited the flowers, day and night, without ever touching or trapping a single one.

We counted 3,636 visits from 17 different types of visitors. Ants turned out to be the most frequent guests, accounting for nearly half of all visits, followed by ordinary flies, then bees, hoverflies, and moths/butterflies together. Each group had its own daily rhythm: most insects were busiest from late morning to late afternoon, but ants were more active at dusk and dawn, and some flies and hoverflies showed two separate activity peaks in a single day. A few visitors, including some beetles and grasshoppers, lingered on a single flower for over an hour, while bumblebees and hoverflies typically stayed just a few seconds. Interestingly, sunlight and temperature had only a limited effect on which insects showed up, flies and ants were less active in bright light, and flies also foraged faster as it got warmer, but most other visitors carried on regardless of the microclimate.

Overall, our results suggest that forest flower visitors avoid competing with each other mainly by using the flowers at different times of day. Beyond the ecological findings, this study shows that filming brambles with cameras is a simple, low-cost, and environmental-friendly way to study forest flower visitors, one that can run continuously, day and night, and could be used to track forest pollinator communities more widely in the future.

 

Read the scientific article in JPE here!