It was fitting that during my visit to the Wells National Estuarine Research Reserve at Laudholm in Maine, on the weekend just before Halloween, that one of my new discoveries was a phenomenon called witches’ brooms. With many of the leaves blown down by the storm we had the day before, these clustered growths were easy to see, and were apparent on several highbush blueberry and honeysuckle shrubs. The “witches’ brooms” are abnormal growths on the branches of the shrubs, forming into dense clusters of stems. The name derives from the fact that this mass of twigs and stems has a broom-like appearance (see photos below).

But what causes witches’ brooms? From what I can gather, they are a sign of stress in the plant. However, depending on the species of plant being affected, the specific cause of the stress may vary. In blueberries, for example, witches’ brooms are caused by a rust fungus (Pucciniastrum goeppertianum), which also affects balsam fir trees. This fungus, spends a part of its life on highbush and lowbush blueberry bushes, and the other part of its life on fir trees. However, both hosts must be present for P. goeppertianum to survive, and spores are be transmitted back and forth between the two host species. Spores from fir trees can be carried by the wind, infecting nearby blueberry bushes. The fungal growth on the blueberry bushes is perennial and systemic and can persist in the plant for years. Conversely, each spring, spores are produced on the witches’ broom on the blueberry bushes that can in turn infect nearby balsam fir trees. Although there is some indication that the fungal infection will weaken the plant over time, the plants I saw with witches’ brooms appeared to be relatively healthy otherwise.

The other surprising thing I noticed during my walk around the Wells Reserve was a slug eating a mushroom. The slug is a fairly common species in New England (most likely Arion subfuscus), so nothing surprising there. And I’ve definitely noticed bites taken out of various mushrooms I’ve come across recently, so something must be eating them. But somehow I had assumed it was mice, squirrels or some other small animal with teeth and the ability to actually “take a bite”. But then I found this little guy enjoying his lunch. Slugs do not possess any of the mouthparts we normally think of (i.e. teeth, mandibles, etc.). Instead, they have a specialized organ common to all mollusks, a radula. This finely toothed radula allows slugs, and other mollusks, to scrape away at their food.

It seems fairly well documented that slugs eat mushrooms, but it is also clear that there is still much to learn. (Click here to read an interesting paper titled What We Don’t Know About Slugs and Mushrooms!) There are numerous references to our friend Arion subfuscus and its mycophagy habits.