3 to 4 inches long fat brown hairless red spots and yellow spots prickly to touch what is it?? (Ontario, Canada)
Your photo is of the Imperial moth caterpillar.
These are found in eastern US, Ontario and Quebec.
This is one of the silkmoth (Saturniidae family) caterpillars…most get very large … rather spectacular in color and size!
This caterpillar feeds on leaves of Bald Cypress, basswood, birch, cedar, elm, hickory, Honeylocust, maple, oak, pine, Sassafras, Sweetgum, sycamore, walnut. It may be heading to find a place in the soil to pupate for the winter.
Adult moths do not feed and do come to lights at night.