I do not want to double post so the link below will point you to the relevant text for this topic. The TL;DR is that the DHT21 type sensors will not reliably work outside in any place that regularly sees relative humidity above 60%. That makes it a poor choice for the inside of a warm bee hive.

The SHT21 from Sensirion and the HDC1080 from TI seem to be good value sensors that have successfully passed our testing at humidities in the 95-99% range.

See the full description at:

Environment Monitor Station Log - Humidity Sensors