Comparing Prionus and Ergates
Although Prionus and Ergates are both large beetles that look very similar, you can tell them apart by examining the spines located behind the head, on the forward part of the thorax.
Prionus has three spines on each side of the pronotum, while Ergates has numerous small spines. Please see the photos.
Ergates. Spiny wood borer has numerous small spines on the pronotum