large round body!,dark brown with light brown speks along its body, big face almost looks like its wearing a mask with huge eyes!
Your photo clearly looks like the elephant hawk moth caterpillar, except it is supposedly only found in British Columbia? Did you find it in Windsor?
There are a couple other sphinx moth caterpillars that look a little like it, specifically the tersa sphinx caterpillar, but also, maybe, the gaudy sphinx (tho this is mostly a southern sp)?
These and your caterpillar have a thick area behind the head that can swell if disturbed, making it look like a snake. This is suppose to scare birds away. The elephant hawk caterpillar has two pairs of “eyes” in this thick area while the tersa and the gaudy only show one major pair.
Elephant hawk moth caterpillars feed on willowherb (Epilobium), bedstraw (Galium), calla, impatiens, and sometimes fuchsias. Tersa caterpillars feed on plants in the Madder family which includes, madder, bedstraw, buttonbush, pentas, buttonweed, etc. Gaudy caterpillars feed on plants in the grape family, and Christmasbush eupatorium.
The sphinx moth caterpillars are also called hornworms since they have a tail (horn on the rear end). Some of these caterpillars lose the tail during the last molt, resulting in an eye-spot where the tail was. When the caterpillars are brown like yours they are probably close to pupating. They tend to start traveling around looking for a soft soil area to dig in and form a pupa. They would overwinter as pupa underground.
The Sphinx moth family has moths that have a triangle shape when they are at rest – most with the shape of a fighter jet. The moths feed on nectar using a long tubed mouthpart called a proboscis that works like a straw. Many moths of this family feed at dusk.
Could you please tell us more about where you found it? what was it eating? how big? what plants were around?