Common Damage Characteristics
Nut Damage | Kernel | Frass | Webbing | Boring | Feeding Behavior | Other |
| Deep Chewing into kernel. | White, often a lot. | Yes, often a lot. | Yes, into kernel. | Larvae feed in groups. Many per kernel. | Shells of heavily infested nuts appear oily. | |
| Deep Chewing into kernel. | Frass at point of entry into the husk. | Very little. | Yes, into husk and kernel. | Single larva feeds per kernel. | N/A | |
| Tunnels chewed into the kernel. | No | No | No | Ants feed in groups. | N/A | |
| Early season infestations may cause shriveled/ Late season infestations do little kernel damage. | No | No | Yes, into the husk. | Larvae feed in groups. Many larvae per husk. | Husks are blackened and shell is stained black. Husks cannot be removed cleanly from shell. | |
| One side of the nutmeat darkened and shriveled. | N/A | N/A | N/A | N/A | One side of husk darkened and shriveled. Husks can be removed cleanly from shell. |
Flowering
Walnuts are monecious, which means that the male and female flowers are on the same tree. Because of this, walnuts are self-pollinating and require no bees. After pollination in the winter, the male flower (catkin) falls off.
Pests
Husk Fly (Rhagoletis completa)
Adult female Husk Fly pierces the husk of the walnut and deposits eggs. After hatching, the maggots feed inside the husk, turning it very soft and black