This is a nymph of some species of Hemiptera, or true bug.
Specifically, this appears to be the nymph stage of a wheel bug (Arilus cristatus) or some other species in the family Reduviidae.
Source: David Larson
Source: Debbie Roos 2005
Here is a picture of an adult (with name-sake dorsal wheel):
Source: Donald W. Hall
You'll notice that the nymph is quite different looking:
Nymphs have been described in detail by Readio (1927). Smaller nymphs are bright red with black marks. The last instar nymphs are darker. Nymphs lack the "wheel" or crest. For a diagnostic key to identify nymphs of the family Reduviidae to genus (including Arilus), see Fracker and Usinger (1949). [Source].
- If you're truly interested in accurately IDing to genus/species, you might check out Fracker & Usinger 1949$^1$, Herring & Ashlock 1971$^2$, or papers that cite their work.
You can find more information about A. cristatus here.
Fracker S.B. & Usinger, R.L. 1949. The generic identification of Nearctic reduviid nymphs (Hemiptera). Annals of the Entomological Society of America 42: 273-278.
Herring, J.L. & Ashlock, P.D. 1971. A Key to the Nymphs of the Families of Hemiptera (Heteroptera) of America North of Mexico. Florida Entomologist 54: 207-212.