What insect bite leaves a welt?
Almost all insect bites or stings leave welts, if they have the horsepower to break the skin. If it's not a chemical blend they inject to make feeding easier, their saliva can also cause a localised allergic reaction. The bite should be expected to increase for a few hours, and then decrease in size and effect in 1-2 days, although some stay longer. Unless the bite expands, changes color, or you experience rashes or shortness of breath (allergic effects), you're pretty safe. However, any allergic reactions -- and especially difficulty in breathing -- mean it's time to call for help.