This is a black walnut tree. My brother noticed them while we were in the backyard. I have other trees that are not black walnut and do not see these bugs on them.
They are red with a black head. Their bodies have ridges on them. It's hard to tell because they are so small. Closer to a large grain of salt, or small piece of rice.
Update: This is from Northeastern Oklahoma area. They have since disappeared. I'm not sure if the heat got to them or they turned into something else or what.
This is a stab in the dark...Scarlet Malachite Beetle larvae. The size wasn't specified but red larvae with black head should be rare...ish? Scarlet Malachite
It would help if you told us where you are situated. However, they are likely to be cardinal beetles, possibly larvae feeding under the tree bark. Totally harmless cardinal beetles
Although I think stormy has a point about the odds of finding more red larva with black heads, I discovered another larva possibility: the walnut caterpillar (Datana integerrima), which seems to be a considerable walnut pest; so, I thought it might be likely.
