Insect bites from various insects, but mosquitos in particular, can cause bruising or dark spots to emerge, as reported by Mayo Clinic. Topical treatments containing cortisone are normally prescribed to relieve the itching sensation and redness, while bio oil is typically recommended to help heal the bruising.
The bruising or itching from insect bites and stings will normally clear up by itself and can be treated at home. Insect bites and stings are normally accompanied with many other symptoms, according to the NHS. In some rare cases, patients can expect nausea, vomiting, sweating, weakness or even an allergic reaction.