Grubs often end up with black spots commonly called "black spot disease." The spots are, however, a symptom resulting from various ills. The black markings are formed by a buildup of melanin and are akin to a scar or a scab. Causes include bacterial infections, bites from certain nematodes and mites, malnutrition, and damage caused by other larvae or the keeper. If numerous spots are seen, the first step is to check and replace the substrate. Larvae that have been poorly kept and fed often end up growing damage spots. so improvements in substrate can be too late. However, most rhinocerous beetles and flower beetles can recover from black spots and become strong, healthy adults. Unfortunately, even just one or two black spots on a stag, jewel, scarab and darkling beetle larvare are usually a death sentence.
