I got stung by a dirt dobber and my arm feels numb.

Here'sTheDirtOnThis. The venom of mud daubers consist of chemicals that function in subduing and paralyzing other insects and spiders used as food for their larvae. They produce their effect on the nervous system of the prey and have little effect on humans aside from causing minor, temporary pain,sometimes more severe. But there is no info regarding your symptom.If it gets worse or is still there tomorrow, see a doc.
Watch. You may be having an allergic reaction. Take diphenhydramine now and every 4 hours. See your Doctor with any worsening. You could get an infection too. Take this seriously. You can have a terrible reaction! .