Preferences and Rates of Feeding in Ariolimax columbianus and Arion rufus

Abstract

Arion rufus was recently introduced from Europe to the Pacific Northwest and may compete for resources with the native banana slug Ariolimax columbianus. I conducted feeding trials with the plants pathfinder (Adenocaulon bicolor), sword fern (Polystichum munitum), lichen (Usnea sp.), and store-bought white button mushrooms (Agaricus bisporus) to observe how similar the feeding preferences were across species, which were more closely analyzed by size class, source population (Douglas-fir forest or grassland), and color morph for Arion rufus. The white button mushrooms were preferred to the other three food choices across all the different source populations. Mushrooms are typically scarce in both the Douglas-fir and grassland habitats so I found this data interesting and compared oven-dried mushrooms and reverse-osmosis water soaked lichen. All the populations preferred the soaked lichen, which may indicate a preference towards texture and moisture rather than a food preference. I observed the effects of temperature on feeding rates among the different source populations. Arion rufus consumed spinach leaves at the same rate across the three temperature treatments (4°C, 10°C, and 20°C); however, the large Ariolimax columbianus may be consuming the least at 10°C. This surprising result suggests that the slugs did not have their typical nighttime feeding temperature as their optimal temperature, nor did they increase feeding rate continually with increasing temperature.