Are snails and slugs normally active only when it's warm and humid? Until recently, my answer to that question would have been a confident "Yes". But thanks to the recent data I've gathered, starting out with some chance observations on a cold morning in Turkey back in October, my current answer would be "They can also be active when it's cold and humid".
Of course, "cold" is a highly relative feeling, mostly dictated by our human sensations. What feels cold to me might be rather comfortable to a snail, if they have roughly equivalent sensations. So to avoid ambiguity, let us dispense with feelings and, instead, set 10 °C as an arbitrary boundary for "coldness". I am interested in the activities of snails and slugs below 10 °C.
Following the light rain we had last nite, I went out around 8 o'clock to check up on the local slugs.
To my surprise and delight–my favorite animals never cease to surprise and delight me–slugs were at it. A particular section of the sidewalk along a forested area was teeming with a particular species that I believe was Deroceras reticulatum.
The temperature right above the wet concrete sidewalk was about 7 °C (the upper number is the relative humidity, which was 100%).
In the nearby woods, the native philomycids were scouring the trunks of the beech trees.
At that location, where I visited slightly earlier, the air temperature was around 8 °C.
Megan Paustian and I are still arguing about the identity of the latter species. Is it Megapallifera mutabilis or Philomycus carolinianus? But that's beside the point. Last nite's observations show that slug activity doesn't cease at temperatures down to about 7 °C.
How far down the temperature needs to go before it gets too cold for the slugs to go crawling? Hopefully, we will find out.