1. By far the most prolific invader, is a false chinch bug of the family Lygaeidae, Nysius niger.
2. Also in large numbers is a green stink bug (Pentatomidae) possibly a species of Chlorochroa (credit to Doug Yanega) and potentially C. uhleri.
3. Lastly, a small green plant bug (Miridae), probably Lygus elisus.
So what do these insects have in common? It turns out that each and every single one of these insects will happily feed on mustards (Brassicaceae). As excellently summarized in a previous blog post by Sarah O. Neill, Brassica tournefortii, or Sahara mustard, is an extremely invasive mustard plant that has become widespread throughout the Southwest. In areas where this mustard has been introduced, it outcompetes native plants leading to a much less diverse community of desert plants for herbivorous insects to graze on. The near monoculture of this invasive weed in some areas of the desert combined with a relatively warm and wet winter season may very well have lead to this remarkable swarm of these three herbivorous true bugs.
Ok, what about the bites and boils? Apart from having a straw-like beak for a mouth one other thing that all true bugs have is paired scent glands. The glands will release a smelly odor when the bug is crushed or otherwise disturbed. Some of the chemicals in these secretions may be skin irritants, particularly for species of Chlorochroa. These bugs may also use their piercing-sucking mouthparts adventitiously to pierce and suck water from your skin in cases of severe dehydration or maybe just when the bug is confused and thinks you look and smell like a plant. Another theory (again...credit to Doug Yanega) is that the bugs are carrying (or are filled with) oils from their mustard host which themselves are irritants.
What should be done? Maybe nature will take of it herself. . .