I believe Beth is talking about the monarchs not being able to "zip" their proboscis together - something that they normally do soon after emergence. The proboscis is actually a paired structure that must be zipped together to form a tube through which the monarchs will feed. No zip = no tube = no drink...try cutting a straw lengthwise and see if you can still enjoy your favorite beverage
This defect is not unheard of and it is most often associated with diseased or parasitized individuals. I would recommend a thorough cleaning/disinfecting of your rearing equipment with a 10% bleach solution. You should also consider isolating your larvae which will help reduce the spread of disease.
Hope this helps!
FYI - additional information about the monarch proboscis is available at