Fall monarch butterflies steer south by the sun, and under cloud they fall back on a magnetic compass that still needs light to work, though not a view of the sun itself. A group at the University of Cincinnati asked whether the summer generations that push the species north each year use one too, and clamped wild-caught monarchs head-down inside a Helmholtz coil that reproduced the local geomagnetic field to see which way each turned as it righted itself. The butterflies righted themselves but picked no direction, and heat did not switch a compass on. Heat did something else: after two days at 35 °C, under a quarter completed the trial, and just under two-thirds managed it after two days back at normal temperature.
A summer-generation monarch on the breeding grounds, with a caterpillar on the stem at right. These are the butterflies the study tested, not the fall migrants that fly to Mexico. Photo: naturelibrarian via Wikimedia Commons.
Exposure note:The coil reproduced the field the butterflies already live in rather than a shifted or cancelled one, so the trial asked whether they read the natural field, not whether an altered field could steer them. Light in the box was diffused and non-directional and carried the ultraviolet component that elicits magnetic orientation in monarchs, leaving the field as the only directional cue.
Quotes
"Monarchs performed negative gravitaxis but showed no additional northward orientation using gravity cues regardless of their treatment, indicating that summer monarchs do not use magnetic cues for orientation, nor does temperature induce a magnetic response."
— Shively-Moore et al., Insects
"In our results, introducing long-term exposure to high temperatures reduced the number of instances where they righted themselves, while short-term exposure to high temperatures had no effect on the behavior of summer monarchs when compared to the control group."
— Shively-Moore et al., Insects
"Although summer monarchs do not use a magnetic compass to orient in later summer generations, the role of other cues is still unknown in their northward range expansion."
— Shively-Moore et al., Insects
Exposure
"In the righting response orientation trials, butterflies were placed inside a Helmholtz coil system that allowed us to control the magnetic field that the butterflies would experience during the trials."
— Shively-Moore et al., Insects, Materials and Methods
"The coils were used to keep the magnetic field consistent with that of the surrounding area and aligned with the local geomagnetic conditions (Cincinnati, OH, USA; 39.134° N, 84.517° W)."
— Shively-Moore et al., Insects, Materials and Methods
Location
📍 United States
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Summer Eastern North American Monarchs Do Not Use Magnetic Field for Directionality but Extreme Heat Alters Righting Behavior
Shively-Moore SA, Chathuprabha BGC, Guerra PA, Matter SF
(2026)
InsectsJournal Level 1ⓘ
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