def update_limits(self):
        """
        Poll 'Service Limits' check results from Trusted Advisor, if possible.
        Iterate over all :py:class:`~.AwsLimit` objects for the given services
        and update their limits from TA if present in TA checks.

        :param services: dict of service name (string) to
          :py:class:`~._AwsService` objects
        :type services: dict
        """
        if self.limits_updated:
            logger.debug('Already polled TA; skipping update')
            return
        self.connect()
        ta_results = self._poll()
        self._update_services(ta_results)
        self.limits_updated = True