They seem everywhere this spring: mite-damaged aloes ranging from dwarf cultivars to tree 'Hercules'. The microscopic pests (Eriophyes aloines) are not insects but spider relatives. They cause deformed flowers, a bubbly fringe on leaf edges, and orange-and-green growths where leaves meet stems.
Google "aloe mite treatment," "aloe mite prevention," "aloe gall" or "aloe cancer" and you'll discover that distinguished experts, landscape designers, succulent societies and growers, and even federal agencies are aware of the problem. Yet they don't agree on what to do about it. Environmentally-unfriendly chemicals supposedly help to some extent, but are expensive, come with cautions, and aren't allowed in certain states (like California).
Mites, protected within galls, are impervious to topical pesticides. To protect rare and valuable specimens, aloe growers and collectors may apply a preventive systemic---a miticide that's taken up into the tissues of the plant via the roots---but it has to be applied before there's evidence that it's needed.
Here's what to do: At first sign, excise affected tissues and bag them for the trash (do not put them in green waste). If an infestation is severe, dispose of the entire plant. After all, it's a breeding ground. Even if you don't mind the galls, do get rid of them before the pests inside them find your neighbors' aloes...or mine. [Update: See expert Duke Benadom's comment below.]
Mites inject a chemical that causes cancerous growth. They produce as many as eight generations a year, and each female lays 80 eggs a month. Mites travel via water, wind, garden tools, and people who find bizarre formations fascinating.
It's not the end of the world. These photos, taken in my own garden, show two different aloes six weeks after gall-removal surgery. I simply used a sharp knife to slice the plants well below any signs of infestation.
Other Pests and Problems
Lush green growth after winter rains means that insects of every kind---indeed, the entire food chain---are proliferating. Find out "What's Wrong with My Succulent?" and what to do about it on my website, my YouTube channel, pages 76-77 of Succulents Simplified and 137-142 of Designing with Succulents.