By Joyce Fry

One recent winter day, my partner, Joyce, and I were birding around our property in northern Franklin County.  Joyce, the ever-alert land manager, noticed quite a bit of woodpecker damage to one of the black willow (Salix nigra) trees that line the pond. Woodpeckers apparently had detected the presence of insect larvae or pupae within its branches and trunk. Arguably, this find is a double-edged sword.  On the one hand, the denizen woodpeckers, of which our local area is home to seven species in the winter, have been well fed; on the other, the damage is an indication that the tree is stressed. Predominately, insects attack stressed trees and plants, which under duress, will emanate volatile chemicals. Perhaps the drought we experienced last August-September (2022), contributed to an insect attack by inducing stress in this tree.    

 According to entomologist and wildlife expert, Douglas Tallamy, Salix species are host trees for wood-boring beetles, and clearwing moths, both of which lay their eggs on the bark of their host tree.  When the whitish, hairless, round-headed clearwing moth larva emerges from its egg, it crawls around looking for access points beneath the bark. It tunnels while feeding, excreting brown frass (fecal material) from the bark as it goes. When its pupal phase is completed, the clearwing adult moth emerges, leaving an empty, brown exoskeleton protruding from the bark.  

Another possible culprit for the insect attack on our black willow tree is a wood-boring beetle, possibly the metallic wood-boring beetle, known as a flat-head beetle as a larva. Female wood-boring beetles lay their eggs in crevices or wounds in the bark.  The whitish, legless flat-headed larva chew through the egg, directly into the phloem layer, feeding on starch and other compounds, the cambium layer, destroying growth cells, and through to the sapwood (xylem), where the conduits for water and minerals reside. They may girdle the trunk or branches with their winding tunnels, leaving packed, brown frass behind.

Both insects inflict much damage during the larval stage of their life cycles.  You may see dieback on or thinning of branches or crown, cankers, calluses, cracked bark, and weakened or broken limbs.  Eventually, the tree may not be healthy enough to play host in the spring to the myriad butterfly species to which Salix have been known to host.  These species include comma, viceroy, red-spotted purple, mourning cloak, and hairstreak.  Salix is second only to Quercus (oak) as host to the most Lepidopteran species. You’ll find S. nigra, S. sericea (silky willow), and S. interior (sandbar willow), all native willow species in Kentucky, along streams, in wetlands, wet bottomlands and floodplains, and along the shores of lakes and ponds.

Joyce’s observation of woodpeckers feeding on wood-boring insect larvae feeding on Salix nigra illustrates an interesting ecological phenomenon known as “Resource Partitioning.” Resource partitioning can be defined as “the division of limited resources by species to reduce competition in an ecological niche.”  In this case, there is obvious pileated woodpecker damage on the lower, larger-diameter tree trunk, while downy woodpecker damage can be observed on its much smaller branches. The pileated, our largest woodpecker, excavated a relatively large hole characteristically rectangular in shape, but with rounded corners, while the downy, our smallest woodpecker, essentially just splintered the branches during its hunt for insect larvae.

This one little observation of damage to a black willow tells a never-ending story of nature’s connectivity and renewal, even in the face of death. The beetles feast to reproduce; the woodpeckers dine on them and reproduce; the black willow will be reduced eventually to frass, soggy wood and sawdust, dropping its branches into the pond; they become food and refugia for aquatic invertebrates; invertebrates become food for frogs, salamanders, and crayfish; they, in turn, provide sustenance for the occasional mink, racoon, and snapping turtle…...to be continued!