Viceroy butterflies look like monarchs to the untrained observer. How can you be sure which species you're seeing?

Wings
The coloring and pattern of monarch and viceroy wings look nearly identical. However, a viceroy has a black line crossing the postmedian hindwing.

Size
Viceroys are smaller than monarchs, although this size difference may be difficult to see in the field. Comparing wingspans:

• Viceroy: 2 1/2 - 3 3/8 inches (6.3 - 8.6 cm).
• Monarch: 3 3/8 - 4 7/8 inches (8.6 - 12.4 cm).

Flight
Viceroy flight is faster and more erratic. Monarch flight is float-like in comparison, with its characteristic "flap, flap, glide" pattern.

Timing
Viceroys do not migrate. They overwinter as 1st or 2nd instar larvae, rolled up in a leaf of their host plant (willow or poplar). In the spring, the larvae need about 15 days to complete the life cycle and become a butterfly. They must develop through the remaining instars (approximately 5 days) and the chrysalis stage (at least 10 days).

• You will not see an adult viceroy where you live until about 15 days after willow or poplar leaves have emerged.

The rate of viceroy development will depend on spring temperatures. Temperatures control how early leaf-out occurs, how quickly the leaves grow, how quickly the caterpillars grow, the chysalis develops and the adult butterfly emerges. Development proceeds more slowly in cooler temperatures and more quickly in warmer temperatures.

Location
Whether viceroy adults have time to develop before monarchs reach you depends on your distance from Mexico. For example, in Minnesota the first monarchs typically arrive by late May but adult viceroys don't usually complete development until June. Whereas in the northeastern United States, monarchs don't usually arrive until mid to late June but adult viceroys typically emerge by late May.