ACT Science Test - Practice Test 2 — Flashcards

Questions below are based on the following information.

The monarch butterfly (Danaus plexippus) migrates south for the winter. In the early fall, the butterflies leave their habitats in United States and Canada and make their journey to sites in central Mexico. In early spring, the butterflies make a return trip to their original habitats across the United States and Canada. This feat, covering up to 4,500 miles, is one of the longest insect migrations in the world. Because of the length of the trip, no single butterfly makes the entire journey. It can take up to five generations of butterfly to travel to and from the wintering sites. Entomologists have proposed three main theories for how the butterflies manage to migrate with such exceptional precision on an annual basis.

Geographical Features Theory:
Monarch butterflies use large geographic landmarks to navigate to central Mexico. These features include large mountain ranges, rivers, lakes, and oceans. Butterflies often roost transiently at these large landmarks during their trip.

Sun Compass Theory:
Monarch butterflies use the location of the sun to orient themselves along the north/south axis. The location of the sun in the sky varies with the time of day and season. Using an internal circadian clock, the butterflies “know” how to orient themselves based on the sun’s location at a given time and season.

Magnetic Compass Theory:
Monarch butterflies have magnetic-sensitive cells in their antennae that orient them along the magnetic north/south axis. During the fall, these cells point them south, and during the spring, they point north. In this manner, the butterflies always have a reliable way to navigate.