Parelaphostrongylus tenuis (brainworm) is a nematode that infects the brain of the white-tailed deer (Odocoileus virginianus). Although the nematode doesn’t usually cause any apparent illness in deer, there is quite a bit of interest in its life history and transmission, because it can also infect caribou, reindeer, sheep, goats, etc., often leading to the death of those animals.
I have some interest in P. tenuis because terrestrial gastropods are the intermediate hosts of the nematode’s larvae. The nematode larvae are found in deer feces and the snails are believed to get infected with the larvae when they crawl over the feces. Presumably, the nematodes pass on to the deer or the other animals when they ingest infected snails accidentally during browsing (I don’t think the deer or the other susceptible animals eat snails intentionally).
Terrestrial gastropods don’t seem to mind to supplement their diets with feces whenever the opportunity arises (for example, read this post and also this one). So, expectedly, several studies have examined the consumption of deer feces by snails. The most recent study that I am aware of is by Garvon & Bird, published in 2005. (Again, I haven’t been that interested in this subject to have spent time searching for more recent papers.)
Garvon & Bird provide a brief review of the previous reports in the literature: one study claimed that the snails were repelled by fresh deer feces, but not weathered ones, while another study claimed that snails were repelled by deer feces containing P. tenuis larvae. The results of Garvon & Bird introduce further confusion. They found that the snail Anguispira alternata was attracted to fresh deer feces whether or not they contained P. tenuis larvae, although the snails seemed to prefer larvae-free feces to those containing larvae.
All of this popped in my mind late yesterday afternoon when I was passing by some deer poop in the woods. So I stopped to investigate.
But my poking around with a stick produced no snails. Perhaps I will have better luck in the spring and the summer.
Garvon, J.M. & Bird, J. 2005. Attraction of the land snail Anguispira alternata to fresh faeces of white-tailed deer: implications in the transmission of Parelaphostrongylus tenuis. Canadian Journal of Zoology 83:358–362.