Moving down the list in alphabetical order: Hemileuca marcata is usually considered a subspecies of hera. H. marcellaria has just dropped out of use as a species name. H. marillia is still found as the name of a species in Mexico, but it's not been studied as a distinct species.
The few sources that have anything to say about it, beyond including it on checklists, say that it's very similar to H. lex. This has been recognized from the beginning. Dyar, who described marillia in 1911, said it might turn out to be a subspecies or even a variety of lex.
The Mexican government may be lumping marillia and mania together with lex. Marillia appears on some checklists but does not rate a separate entry in Mexican museums or university libraries today.
When the top 20 search results for a species include a post that appeared at this web site, a decade ago, and what that post had to say about marillia was:
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Hemileuca marillia Dyar, 1911A formal scientific bulletin described this species as "known only from a single specimen found in La Paz, Lower California."
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...you know the state of the science is very poor. The Internet has now been enriched with a copy of Dyar's original description of the species, which disclosed that he knew it from study of four museum specimens, two male and two female.
Dyar descried marillia as distinguished by its "rosy" color. Upper fore wings and bodies varied from "rosy brown" to pink. Hind wings were brown. The few photos I found, of museum pieces, show a persistence of rosy color in some specimens while others fade to gray; they look very similar to mania. The wing span ranged from a little over 2 inches to about 2.5 inches.
Dyar also mentioned a species he called H. dukinfieldi. What became of that one I have yet to learn. It appears neither on the earliest lists nor on any recent ones.
The early stages of marillia's life have never been documented.
Mention should, however, be made of an early twentieth century US government pamphlet that included marillia as probably yet another subspecies of the draaded "New Mexico Range Caterpillar," Hemileuca oliviae, which apparently went through a local population explosion about a hundred years ago. What needs to be kept in mind, as one reads this historic document, is that the writers knew nothing at all about the early stages of most of the twelve species they included under this English name. All the Hemileucas are similar in some ways, and to know the caterpillars is to loathe them, but the writers' fears of this species seem unrealistic today.
Their primary concern was that "Range caterpillars" ate grass and would poison sheep or cattle who inadvertently consumed them. The writers resisted another exaggerated fear, that "Range caterpillars" would be a serious pest on grain crops. They were not, even during the population explosion. The desert sand could become hot enough to kill caterpillars crawling on it in the afternoon, the writers explained, and as the sand heated up the caterpillars would try to climb up anything they could reach to take their siesta, so they might be a nuisance in a grain field, but they didn't eat any plant that was cultivated for grain crops.
However, the writers observed, "Range caterpillars" were basically, well, stingingworms. They are not a cute, lovable species like Woolly Bears or tent caterpillars. According to the writers, all twelve species, most of which the writers admittedly had never seen, shared the same repulsive character traits. They were "wasteful eaters," biting off more grass than they even tried to eat, swallowing ore grass than they digested--bits of undigested grass, still green, were visible in their frass. They chomped vigorously at the tough semi-desert grasses they ate, their jaws making "an audible click." They were large, about two and a half inches lng, with bristles making them as thick as a man's finger and a tendency to look even bigger than they were. They seemed, and this raises eyebrows because it's not observed under normal conditions, to quarrel and fight with one another, two caterpillars trying to sting each other by pushing their upper sides against each other, but to be unable to do each other any harm. When picked up in the fingers, they would squirm vigorously, trying to sting the researcher's hand as badly as possible. The writers thought that stingingworms had voluntary control of the venom sacs at the bases of their bristles, which remains unclear today. They were unaware of anyone's having a serious reaction to being stung, though; they wrote guilelessly that if the caterpillars stung sensitive skin, as it might be the inner surface of the elbow, the inflammation might last an hour or two. Worst of all, during the population explosion one had to walk carefully to avoid stepping on the little menaces.
Really, if a person's boots were sturdy enough, why would one want not to step on stingingworms? I suppose the idea was that cowboys didn't always take off their boots when they came indoors. During a population explosion like the one described, the public-spirited thing to do would have been to crush as many caterpillars as possible with sticks.
The writers might have been uncomfortably aware that this early population explosion had been produced by trying to "control" the caterpillars with poison sprays. Theoretically that's certainly possible, though nobody seems to be admitting having done it. They did not recommend spraying anything, but found hope in the large percentage of stingingworms they had found being parasitized. Internal parasites have remained the most effective check on Hemileuca populations unto this day.
So, does or did marilia live on grass and present a risk of food poisoning for cattle? Does it sting in an aggressive, intentional way, or merely turn its bristles out when it curls up and plays dead? What, in fact, does it eat? Nobody seems to know. The writers of the 1918 document simply assumed that it was the same sort of thing as oliviae. What we've learned about the Hemileucas since then is that the differences among the types that look like separate species is produced by the caterpillars eating different food in different climates. Marillia seems to be another desert dweller that at least has a healthy instinct to stay away from humans, probably the most likable quality a Hemileuca can have.
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