According to "The Bhikkhus' Rules: A Guide for Laypeople" by Bhikkhu Ariyesako:
The Buddha suggested that the basic source of food for bhikkhus was that received on the morning alms round (pi.n.dapaata). This daily dependence on alms food reminds both the bhikkhus and the lay devotees of their interdependence and prevents the bhikkhu from becoming too isolated from the lay community. He 'meets' them every day and eats the food that they share with him. Several important rules are concerned with this as well as a major section of the Sekhiya Training rules.
On this page, āraññika dhutaṅga refers to:
"the one who has the habit to dwell in a country side lodging remote from villages", that is to say the one who lives remote from inhabited areas.
And the ukkaṭṭha āraññika, the noble practitioner of the āraññika dhutaṅga is defined as:
The bhikkhu who is a noble practitioner of the āraññika dhutaṅga is resolved to dwell and dwell into a forest monastery (remote from inhabited areas) a all the time, during the three seasons of the year that are summer (from March to June), the monsoon (approximately from July to October) and winter (approximately from November to February).
The "The Bhikkhus' Rules: A Guide for Laypeople" also states:
In the Buddha's time some ladies were ambushed and raped on their way to give food to bhikkhus living in a dangerous jungle area. Their family criticized the bhikkhus for not warning them of the hazards. If lay people intend to give food to a bhikkhu(s) in such a danger zone then they must announce that to the bhikkhu(s) beforehand so that the bhikkhu(s) has a chance to warn them or reduce the threat.
The rule can be summarized: "Eating an unannounced gift of staple or non-staple food, after accepting it in a dangerous wilderness abode when one is not ill is [an offence of Acknowledgement.]" (Paatidesaniya 4; BMC p.488)
So, how does an ukkaṭṭha āraññika get his food? Only from lay people who dare enter the potentially dangerous forest area to give them food or can they eat food that they can find in the forest like fruits?
If they eat fruits etc. in the forest, wouldn't that be a violation of another rule requiring the monk to get his food from alms?
Here, I assume that an ukkaṭṭha āraññika does not go to inhabited areas for alms, by the very definition of "ukkaṭṭha āraññika".