The beautiful bright red berries of American holly attract many fascinating feathered friends such as mocking birds, blue jays, and cardinals to a winter feast. The berries provide a nutritious meal and, in return, the birds distribute the holly to new places by depositing seeds in their droppings. While photographing the native holly leaf miner
that we met in an earlier episode of Bug of the Week, I spotted several holly berries distinctly green rather than scarlet red. Inside these fruits, were tiny yellow maggots, the larvae of the holly berry midge. In the spring when hollies were in bloom, the adult holly berry midge, a small mosquito-like fly, deposited eggs into the developing fruit of the holly. These eggs hatched into larvae that fed within the berry. During the past growing season, the maggots consumed tissue of the fleshy fruit. In winter, larval development slows, but when the warmth of spring returns, these maggots will complete development and become pupae from which emerge small midges that mate and deposit eggs into the developing berries, thereby completing the cycle of life.
For a small maggot, life in a holly berry is precarious. Its fate is tied to a red berry that advertises, "eat me" and hungry birds and squirrels happily oblige. These frugivores could literally eat the holly berry midge out of house and home. However, the larva of the holly berry midge has a neat trick to lessen its risks of disappearing down the gullet of a bird along with its fruity home. Berries infested by the holly berry midge fail to turn red as do normal holly berries. The midge and an associated fungus prevent the formation of bright red pigments by the berry. Infested berries remain green all winter. Through a series of detailed observations, researches found that green holly berries were much less likely to be eaten by squirrels and birds than red berries on the same tree. By preventing the berry from turning red and avoiding the attention of fruit eating critters, holly berry midge has found a way to enhance its chances for survival. So as you decorate your home with boughs of holly and you spy a green berry, you will understand why green is good for the clever holly berry midge.
The interesting article “Selective Avoidance by Vertebrate Frugivores of Green Holly Berries Infested with a Cecidomyiid Fly (Diptera: Cecidomyiidae)” by Vera Krischik, Eric S. McCloud and John A. Davidson was used as a resource for this episode.