QUESTION: Bob, I've emailed this photo to see if you might know what's growing on the poor doe. I took the photo while out driving in Potter County, Pennsylvania. I thought about putting this doe down, but wasn't sure what a warden would do once I reported it. - Jeff H.
ANSWER: While I can't be certain without examining the animal, the gross lesion on this deer appears to be something called a cutaneous fibroma - essentially a benign tumor or wart believed to be caused by a papillomavirus, which would likely be transmitted by a blood-sucking insect.
Fibromas are typically dark gray or black, though they might occasionally be un-pigmented, tan or white.
However, fibromas might show more red, particularly if they are scratched and bleeding. Abrasion could also result in secondary infection, which might be the case with this deer.
Fibromas are more common in younger deer. The initial infection stimulates an immune system response in the host deer, and eventually the fibromas cease growing, then dry up and go away. If this is the case, the deer should survive and be just fine.
Larger fibromas can affect a deer's health if the growths are large and interfere with sight, breathing, eating or escaping danger.
As for putting any animal down, you did the wise thing by not taking matters into your own hands. It's always best to consult your local game warden before taking action. Be sure to add the number of your closest fish & game office to your phone's address book so you can contact them quickly. Better safe than sorry.