Thursday, September 22, 2011

S is for Snakeroot

One of the plants blooming profusely at the moment is White Snakeroot (Ageratina altissima). Snakeroot is comfortable in a variety of habitats, from thick shade to partial sun. It is especially at home in open woods and thickets, but I have also seen it growing in more open areas. Snakeroot produces clusters of small white flowers on long stems. Its leaves are vaguely heart-shaped and roughly toothed. Snakeroot is one of many species that were formerly grouped in genus Eupatorium, so you may occasionally see its scientific name given as Eupatorium rugosum in older publications.

Snakeroot seems to be much unloved. Part of the reason is its weediness; it often grows in dense patches, spreads rapidly, and can take over an area if left unchecked. While I appreciate the beauty of its white flowers, the large, rough leaves might not be aesthetically appealing to everyone. Another reason for its poor reputation may be its toxicity. White Snakeroot produces tremetol, a toxin that produces severe intestinal distress if it is ingested. In the 19th century, tremetol often poisoned humans who had consumed milk from cows that had eaten snakeroot, a disease known as milk sickness.

Despite its bad reputation, not every animal is harmed by the plant's toxins. Many insects find snakeroot useful for food. According to the HOSTS database, five species of moths have been recorded using White Snakeroot as a larval hostplant. They are Clymene Moth (Haploa clymene), a leaf blotch miner moth (Leucospilapteryx venustella), Hitched Arches (Melanchra adjuncta), Ailanthus Silkmoth (Samia cynthia), and another silkworm moth (Samia walkeri).

Besides that, many insects use snakeroot for nectar, like this Asian Tiger Mosquito (Aedes albopictus). I have also seen various bees and hoverflies nectaring at snakeroot, but I cannot find an image from my files.

Others just rest on its leaves, like this picture-winged fly (Delphinia picta).

Yesterday I found something I had not noticed before in the snakeroot patches in the backyard. Many snakeroot plants had long lines of tiny aphids up and down the stems. Of course, where there are aphids, there are likely to be ants, so there were also many ants walking up and down the stems to tend to the aphids. Thanks to Alex Wild for identifying these as winter ants (Prenolepis imparis). Click through the photo above to see more of the ants.

There was a particularly dense cluster of aphids near the top of the plant, and there were ants along with them. This cluster was harder to photograph because the flower head was in the way. While snakeroot may be nutritious to some insects, I still would not suggest eating it yourself. However, unless there is a risk of accidental ingestion (by a pet or small child, for example), it may be worth leaving some snakeroot in place for insects to use.