Mullein Weevils

As anticipated, Julia and I have been filling our front yard with fruit trees and a vegetable garden, and letting most of the remaining lawn grow into a meadow–not out of laziness but from a desire to turn this sterile mini-landscape into habitat for something. Already, the monotonous carpet of green has given way to an ever-shifting array of flowers, attracting multitudes of nectar- and pollen-seeking bees, flies, and butterflies. The taller plants provide cover for toads and all sorts of insects and spiders, as well as perches for damselflies and dragonflies like this calico pennant (Libellulidae: Celithemis elisa) that showed up yesterday.

Every additional species of plant that is allowed to grow, whether a native wildflower or a European “weed,” further increases the diversity of our yard by providing food for its own suite of host-specific insects. For the most part, the native plants do a better job of this, but even this meadow dominated by European plants is a tremendous improvement over closely cut grass.

In the above photo, the yellow flowers are common cinquefoil (Potentilla simplex). I collected some cinquefoil leaf mines here when we first came to look at the house last May, and the adult agromyzid flies emerged four months later, after we had moved in. The white flowers are lesser stitchwort (Stellaria graminea), the presumed host of this chickweed geometer. The big rosette in the middle of the photo is common mullein (Verbascum thapsus), and it’s just beginning to send up what will be a tall stalk covered with yellow flowers. When I peeked down into the center of the rosette yesterday, I found it covered with little brown weevils.

I’m a sucker for weevils in general, but I thought these furry ones were particularly adorable.

Can you spot the female in this pile?

I had never seen these weevils before, but I had a hunch they were connected with something I saw while walking along a trail in Vermont in early August, 2005. A downy woodpecker was pecking open the seed pods on a mullein stalk, and whatever it was finding in there was exciting enough that it let me get within a few feet of it as I watched it forage. Every stalk nearby had similar ragged feeding holes opened up in many of the pods.

After the woodpecker had left, I opened up one of the intact pods and found a weevil pupa inside.

I later learned that the larvae of Rhinusa tetra (Curculionidae; formerly Gymnetron tetrum) develop inside the seed pods of common mullein and pupate there when they have finished feeding. A quick check of online photos of this species seems to confirm that this is the weevil currently congregating on the mullein in my yard. I looked at the other mullein rosettes there, and a few others I came across at work today, and every one of them was similarly covered with these weevils.