Detecting magnetic fields A magnetic field is invisible, but it can be detected using a magnetic compass. A compass contains a small bar magnet on a pivot so that it can rotate.

More information: Samuel A. Shively-Moore et al, Monarch butterflies (Danaus plexippus) only use magnetic cues for migratory directionality with orientation re-calibrated by coldness, PLOS One (2025).

Biologists find captive sharks can sense magnetic fields. Finding adds evidence sharks use an internal compass to navigate across oceans. CBC News · Posted: Dec 15, 2004 1:35 PM EST | Last ...

(Marjorie Miller/Associated Press) A new study suggests that monarch butterflies use an internal magnetic compass to help navigate on their annual 2,000-mile migrations to central Mexico.