When I was a kid and had just moved to Florida, my mom starts yelling for me to "come here and see this!" It was a great big blob of bird shit on the lemon tree in our back yard.
I'm all, "yeah, that's a big blob of bird poop alright." Then she poked it and the devil's face came out from under it's ass. Bright red and pointy horns.
It was an orange dog caterpillar or Giant Swallowtail. Papilio cresphontes.


Those weird things that they stick out are apparently also some sort of scent gland and give off a strong citrusy smell.