from Why We Eat What We Eat, p. 33:
...But the most dramatic pre-Hispanic culinary contribution of the maguey to modern Mexican gastronomic life is entomological: the worms that infest the plants' thick pointed leaves and its roots. Sahagun mentioned both: "There are some worms they call meocuili, which means maguey worms. They are very white and they grow in the magueys; the cut a hole and go inside, eating and sending out their excrement through the hole by which they entered. They are very good to eat." (11.13.81)
These worms (really larvae) are also known as palomillas de maguey (maguey squabs), champolocos, meocuilines, pecahs, or scientifically, Aegiale (Acentrocneme) hesperiaris...
Worms harvesters (I paraphrase the account in Teresa Castello Yturbide's magnificent and sometimes terrifying Presencia de la comida Prehispanica...Banamex, 1986) poke about among the maguey's lower leaves, looking for the telltale worms tunnels at the base of the leaves near the outer edges. Working very carefuly with a machete so as not to disembowel the worms unwittingly, they cut open the leaf. To extract the worms whole, they use hooks formed by cutting thin strips from the edge of a maguey leaf. They remove all of its spines except for one at the end of the strips. This they form into the hooks they use to catch the worms by the head. To store the worms they make pouches with the skin of a tender new maguey leaf that looks like parchment and is called mixiote. (It gives its name, synecdochically, to a dish made of chunks of marinated meat wrapped in mixiote pouches and steamed).
To cook the worms, people sometimes just put a whole gusano-filled mixiote over coals or hot ashes, or they might just put the worms directly on a bakestone (comal) until they swell and stiffen, turning golden brown and crunchy. And this is not some quaint acccount of a long-forgotten practice. Castello Yturbide nonchalantly mentions that maguey worms can be obtained in April in the market of San Juan in Mexico City, on Wednesdays in Actopan, or Mondays in Ixmuquilpan..., or in farm hamlets around Mexico City.