Brown recluse spider- these spiders are usually found in areas in your home where there is low traffic. Many people who are bitten cannot figure out where the bite may have taken place.
The spiders venom can cause severe progressive tissue destruction leading severe potentially deforming areas of tissue death that can go from the skin to the deeper layers of muscle. Fortunately, most people and animals develop smaller more manageable lesions.
It can be very difficult confirm in an affected pet whether any lesion is due to a venomous bite or sting..but a spontaneous expanding lesion that is usually somewhat circular is very suggestive of a venom.
Treatment varies with severity and progression of the bite wound area and can be very simple or very drawn out if massive tissue damage takes place.
Best prevention is to be cautious and perhaps when entering areas and rooms that are less frequented and wear gloves and long sleeves and pants with socks and shoes when cleaning or moving things around in these areas.