I was collecting some Black Walnut leaves for the Luna Moth Caterpillars I am raising (that’s another story!) and I came across what I thought was mold. After taking a closer look – they are caterpillars! A lot of them! Turns out I think they are Hickory Tussock Moth Caterpillars and will only eat the leaves from black walnut, pecan, hickory and butternut. They can cause mass destruction and if they eat too much earlier in the season, they could cause permanent damage to the tree, even killing it. Most research says to kill them but I will keep my eye open for more masses and spare them for now. I have only seen this one patch.