The dusky slug, Arion subfuscus, feasting on the fruit of a Virginia creeper (Centennial Woods, Burlington)

Slugs on the prowl

Note: this post is the answer to a natural history quiz I posted to my instagram account. Follow me to get weekly natural history quizzes.

Question: One species is eating another. What are the two species in the above photo?

If you thought the fruit was a “Grape” you were both right and wrong. The fruit – technically a berry – belongs to Virginia creeper, Parthenocissus quinquefolia, which though not technically a grape (genus: Vitis) is in the grape family (Vitaceae). The berries of both grapes (Vitis spp.) and Virginia creeper ripen in the fall, at which point they start getting plucked from the vine by migrating birds (e.g. catbirds) and some winter residents (e.g. cardinals). Like the seeds of many other berry-producing plants, the seeds of Virginia creeper have significantly higher germination rates if they’ve passed through the gut of a vertebrate. The stomach acids help the seed break dormancy by breaking down the seed coat, exposing the seed to water, sunlight, and oxygen, all of which are essential for growth of the seedling.

Unfortunately for the parent vine, not all Virginia creeper berries make it down the gullet of a vertebrate. Some getting blown to the ground by strong winds (like we had last week), others are knocked off by squirrels, while many just shrivel on the vine. For many of those that fall to the ground, the sweet part of the berry is slowly nibbled apart by invertebrates, leaving the seeds bereft of a dark windy trip through a digestive tract. Without the seeds passing through a digestive tract, the plant’s chances of passing its genes on to a subsequent generation are slim. Here, a dusky slug, Arion subfuscus, is thwarting the plans of Virginia creeper.

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