Nettles are commonly found growing near the banks of Pennypack Creek. At least two varieties are found here. Wood Nettles (Laportea canadensis) have broader flat leaves, while the Stinging Nettle (Urtica dioica) has narrower leaves. Both prefer wet environments and tend to grow along Creek Road near the stream banks. Like other plants which flourish in the Pennypack Preserve they are deer-resistant. In this case, deer are deterred from eating them by an extensive cover of stinging hairs over the stalk and stems. People are similarly deterred from touching them. However, despite these defenses, nettles are not immune from predators. Amber snails are able to climb the stalk, seemingly oblivious to the stinging hairs, and feed on the nettle leaves.
So far, I have only seen these snails on wood nettles. Amber snails (probably Succinea ovalis), similar to the nettles they feed on, love moisture and tend also to be found close to the water. The name apparently comes from the appearance of their translucent brown shells, similar to amber. Nettles are apparently appealing food to a number of snail species.
Further down the trail I saw some Wood Nettle plants which looked like someone had dropped green pearls on the leaves.
At first I thought they might be eggs, but they were hard and firmly attached to the leaf. In fact, these are insect galls. While we typically think of galls from gall wasps, these are from a small fly, the gall midge (probably Dasineura investita). The gall midge lays eggs on the leaf, typically over a vein. This initiates a reaction from the leaf which forms a protective coating around the egg or larva. The larva lives in the gall where it receives some protection until it matures and leaves the gall. Unless superabundant, the galls are otherwise not harmful to the leaf. This species of gall midge apparently prefers nettles as its host. Galls can be seen on numerous other leaf types in Pennypack Preserve. Wasps are the more common source. The appearance of the gall seems to be specific both to the host species and the insect which produces it.
1 thought on “Wood Nettle Ecology”
Spectacular merger of text and images to tell a story quickly and effectively.
Wonderful job!