Congratulations to “mariagianferrari,” who came the closest to solving the Mystery Photo when she correctly guessed that the missing bark was the result of a partnership between an insect and a Yellow-bellied Sapsucker (Sphyrapicus varius). The sapsucker arrived first and pecked the vertical rows of rectangular holes in the trunk of the tree in order to obtain sap as well as the insects that the sap attracts. (Usually these holes are not harmful, but a tree may die if the holes are extensive enough to girdle the trunk or stem.)
The second visitor whose sign is apparent between the sapsucker holes is the European, or Giant, Hornet (Vespa crabro). This large (3/4″ – 1 ½ “) member of the vespid family was introduced to the U.S. about 200 years ago. Overwintering queens begin new colonies in the spring and the 200-400 workers of a colony then forage for insects including crickets, grasshoppers, large flies and caterpillars to feed to the larvae.
In addition, the workers collect cellulose from tree bark and decaying wood to expand their paper nest, which is what has occurred between the sapsucker holes, effectively girdling the apple tree. The nutritious sap that this collecting exposes is also consumed by the hornets. We don’t often witness this activity because most of it occurs at night.
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If you find a football-size (or larger), gray, papery structure attached to the branches of a tree or shrub, you’ve probably discovered the nest of a bald-faced hornet. (The only other hornets that build a similar nest are aerial hornets, and their nests usually have wider strips, and less of a scalloped appearance than those of bald-faced hornets.) This structure is actually a nursery, filled with several horizontal layers of hexagonal cells, in which eggs are laid and larvae are raised. These horizontal layers are surrounded by a multi-layered envelope, which, like the cells, is made of masticated wood fiber from weathered wood such as fence posts and hornet saliva. The different colors reflect the different sources of wood that have been used. Although only the queen bald-faced hornet survives over winter (in a rotting log or other protected spot), the workers do not die until freezing temperatures have really set in, so wait for another month before approaching a nest!