Check the type of tires it has. The link below should help. If the tires are meant for dry cruising, they’ll be terrible in the wet.
Check also your tire pressure. If it’s too high, you’ll spin easily.
lastly, jack up the back end, spin the wheels by hand, and see if you have a dragging brake. A dragging brake on one wheel will cause ready spinning of the other wheel.
http://www.tirerack.com/tires/tiretech/techpage.jsp?techid=33