Monarchs usually arrive in Mexico by the 1 November Day of the Dead holiday. Legend says their arrival signifies the returning of the spirits of the dead.
Millions of monarch butterflies are making their annual migration from North America to Mexico, although its wintering grounds have dropped to around one-third of last year's levels due to illegal logging, experts said on Monday.
Mexico has clamped down on illegal logging, but officials say the number of personnel guarding a butterfly reserve west of Mexico City has been cut from 180 to 25, as part of a government austerity programme.
Environmentalists and officials still expect a strong turnout this year however, in part because of a 2018 population rebound.
The butterflies make the 5,472-kilometre migration journey from the United States and Canada each year and then return northward, although no single butterfly lives to make the round trip.
Monarchs usually arrive in Mexico by the 1 November Day of the Dead holiday. Legend says their arrival signifies the returning of the spirits of the dead.