Willow Pinecone Gall

What is this interesting botanical object, you may ask? A fuzzy pinecone growing on the end of a branch? My research revealed one of nature's curious and complex wonders.

They aren't pinecones, but rather the protective homes of the Willow Pinecone Gall Midge (Rhabdophaga strobiloides) - a type of gnat/fly that relies on willows for its home. The adult gall-midge lays its egg on the tip of a willow branch as the buds begin to swell in the early spring. The egg and larva that hatches, release a chemical that tricks the growing willow leaves into forming a structure that looks superficially like a pinecone made of overlapping leaves. As the larva feeds, the bud ceases to develop, but the willow plant still directs nutrients to the tissues. Biologists working at the University of Michigan Biological Station at Pellston, Michigan found that somehow the gall-midge manipulates the willow to provide resources from other places in the plant to the gall for them to continue to feed and survive. The larva continues to feed and grow. Once winter sets in, the larva is encased in the cone structure - protected from predators, but not from the cold. The larva aren't freeze tolerant. Instead, they rely on extreme supercooling - the process of lowering liquid temperatures to below the freezing point without becoming a solid. How do they do this? Overwintering willow gall larva can contain as much as fifty percent glycerol, historically used in cars as anti-freeze. At some point in the spring, the larva will pupate and the adult gall-midge will emerge. They don't have mouthparts to chew their way out of the gall. Instead, they simply push and squeeze between the overlapping leaves of the gall and fly away.