Southern France — Provence, the Mediterranean coast, and much of the south — gets genuinely hot in summer, with the same heatstroke risks as anywhere in southern Europe. Watch for heavy panting, drooling or lethargy, keep walks to early morning or evening, and never leave a pet in a parked car, even briefly.
Ticks are common across rural and wooded parts of France, particularly in spring and autumn, and carry some of the same risks as elsewhere in Europe. Check your pet's regular tick prevention is current before travelling, and check coat and paws after a walk through long grass or woodland, especially in regions with significant forest cover.
The processionary caterpillar hazard, covered in its own article in this section, is specific enough and serious enough to warrant separate attention — it's a different kind of risk from heat or ticks, and worth reading on its own rather than folding into general outdoor safety advice.