The Louisiana fox squirrel,Sciurus niger ludovicianus Custis (SKY-your-us NIGH-jer loo-doh-vee-kee-AYE-nus;"shade-tail black [of] Louisiana") is the only mammal Custis observed that is now credited to him, although he was the first to observe three distinct species of squirrels — a division not recognized by other naturalists until the middle of the twentieth century — and provided an accurate, if much abbreviated, description of this one.1 This mammal's generic name, Sciurus, indicates the use of its tail for shade when resting.
Certainly Custis did not go into as much detail in any of his descriptions as Lewis almost routinely did. As Professor Flores points out, Custis was not an experienced field naturalist, and his published summary of his observations, as edited by Nicholas King, was essentially worthless.1
The fox squirrel is the largest of the tree squirrel species, reaching an average maximum length of 27 inches. Its underfur is black on the upper part of its body, but the coarse guard hairs being tricolored, especially in the northern part of its geographical range, may give its coat a grizzled effect. Its ears, cheeks, throat and underparts are typically reddish-yellow or yellowish-brown, or buff. The characteristically long, reddish bushy tail from which the fox squirrel takes its common name, is obscured in this photo.
1. Dan Flores, Jefferson & Southwestern Exploration: the Freeman & Custis Accounts of the Red River Expedition of 1806, (Norman: University of Oklahoma Press, 1984), 228-29 and note 87