Bumble bee wax melts between 34º - 40º C (93º - 104º F) compared to the 62º - 66º C (143º - 151º F) melting temperature for honey bee wax. According to the books, bumble bees mix pollen with their wax to improve its strength.
http://www.fao.org/docrep/w0076e/w0076e12.htm