Two separate systems that have to work together
Seasonal migration in insects depends on inherited timing: circadian and photoperiodic clocks trigger developmental and behavioral changes, including correct flight orientation during long-distance migration [1]. Separately, migrants appear to use an internal compass sense to assess direction during long journeys [5]. These are different jobs. The seasonal clock decides that autumn is the time to head south; the compass decides which way south is at any given moment.
The two systems meet in the sun compass. Because the sun's position shifts through the day, a compass that simply flew at a fixed angle to the sun would drift off course. A time-compensated compass uses the insect's internal clock to correct for that shift, and circadian clocks in the antennae have been shown to allow autumn migrants to time-compensate their sun compass [1].
The antennae as the clock behind the correction
The clearest evidence for the time-compensation mechanism comes from monarch butterflies. Antennal circadian clocks coordinate sun compass orientation during the fall migration, and butterflies whose antennae were removed showed disoriented flight behavior [4]. That result ties a specific piece of anatomy to the correction step: without the antennal clock, the sun compass no longer holds a steady heading.
The same study notes that a similar process may extend to other insects such as bees and ants [4], but that is presented as a possibility rather than a demonstrated generality. For monarchs, the link between antennal clocks and compass orientation is direct.
How seasonal cues feed into the compass
Seasonal change does not just switch migration on; it also shapes the orientation the compass produces. In monarch butterflies, the direction of travel changes with the seasons, and the butterflies start their northward spring migration under seasonal cues, with sun-based information integrated into directed flight behavior [2]. In other words, the inherited seasonal program sets the target direction, and the sun compass executes it.
The neuronal mechanisms underlying sun compass orientation are an active area of study, and genetic factors behind migration are being identified [3]. That work is about how the compass is built and wired, not about whether it exists; the behavioral evidence for sun compass orientation in migrants is already established.
Why the combination matters over thousands of kilometers
Long-distance migration can span thousands of kilometers, and insects high in the air are hard to observe directly, which is why systematic observation of flight behavior at altitude matters for understanding how migrants steer [3]. The picture that emerges is a division of labor: inherited seasonal timing sets when and roughly where to go, and a clock-corrected sun compass keeps the heading accurate as the day wears on [1][4].
What remains less settled is how widely the antennal-clock mechanism applies beyond monarchs, and how sun cues are combined with other sensory information in the brain [2][4]. Those are open questions about mechanism and generality, not about whether inherited timing and time-compensated sun compass orientation both contribute to insect migration.
Sources used in this answer
Keeping time without a spine: what can the insect clock teach us about seasonal adaptation?
Insect circadian and photoperiodic clocks govern seasonal behaviors including diapause and correct flight orientation during long-distance migration, and circadian clocks in the antennae allow autumn migrants to time-compensate their sun compass.
Neural coding of different visual cues in the monarch butterfly sun compass
Monarch butterflies change travel direction with the seasons and begin northward spring migration under seasonal cues, with sun-based celestial information integrated into directed flight behavior.
Long‐range seasonal migration in insects: mechanisms, evolutionary drivers and ecological consequences
Long-distance seasonal insect migration involves sun compass orientation and genetic mechanisms, and understanding it requires systematic observation of flight behavior high in the air.
Antennal circadian clocks coordinate sun compass orientation in migratory monarch butterflies
Antennal circadian clocks coordinate sun compass orientation during fall migration in monarch butterflies, and removing the antennae disorients flight behavior.
Riders on the wind: the aeroecology of insect migrants
Insect migrants undertaking long-distance seasonal journeys appear to use an internal compass sense to assess direction.