This is an early instar of the caterpillar which will eventually grow to about 9cm! This one was quite small. It is also called Elm Sphinx as its main food is elm,though it will feed on basswood too. Both trees are abundant at the conservation area. The name 'four-horned' comes from the two pairs of 'tufts' near the head (which is on the left side in this photo). The so-called horn on the other end is a feature of sphinx caterpillars.