Is there an insect bite that causes bruising?

Yes: Certain insects, when they sting or bite, actually inject an anticoagulant material into the area so the blood flows to them more easily. This can lead to leaving a bruise in the area after the bite/sting. Best thing is cold compress or even ice pack initially, then after a few days switch to warm packs to help bruise resolve.

Agree w Dr. Maes: Insects whose bites or stings may cause bruising include: Horseflies, Deer flies, mosquitoes, wasps, bees, scorpions, Black Widow spiders, Hobo Spiders, Brown Recluse Spiders, ticks. In some, this can evolve into more sinister lesions.