1. Migration Routes

There are three migration routes:

1. From the west of the Rockies to Southern California and Baja.

2. From Florida towards Yucatan – exactly where they hibernate is still not known.

3. From South East Canada and North East USA to the hibernating area in the Western Sierra Madre Mountains of Michoacan, Mexico. Approximately one hundred million migrate this five thousand kilometres every year.

The Mexican monarch migration is the longest of any known insect.

It was a mystery until 1975 exactly where these butterflies migrated. A Canadian discovered the location after a systematic search that had started in 1938.

2. Life Cycle

There are four stages in a Monarch’s life:

1. The egg – these are laid on the underside of the leaves of the milkweed plant. After a week a caterpillar emerges.

2. The pupa (caterpillar) – after about three weeks of feeding on Asclepias or Milkweed it looks for a suitable branch in which to form a chrysalis.

3. The chrysalis - after two weeks inside the chrysalis the caterpillar is transformed into a butterfly and flies away.

4. The butterfly – the mature adult may live as long as nine months.

It takes between five to eight weeks to complete the cycle. However, different generations take different times. Thus it is possible for a migrating adult to live for up to nine months (but most live only a few months).

3. In the North

During their stay in the north, three to five generations of butterflies develop. The last of these, which are born during September and October, is the generation that will travel south.

Monarch populations can either stay in the northern nursing sites and breed or continue their journey south.

4. Migrating South

The arrival of the butterflies in the hibernation areas starts at the end of October.

For long distances they make use of air currents to glide rather than fly. They prefer following green valleys and try to avoid hills and mountains.

They fly at an average of 13 miles an hour as high as 160 feet over flat ground and up to 30 feet above hills and mountains.

5. Hibernation In The Mexican Reserves

There are five conservation areas. To be effective each area needs to be at least ten square kilometres with a minimum of about four hundred mature trees per hectare.

Approximately seven to twenty million butterflies arrive in each of the five sites.

Tourists are only allowed to visit two of the sites: Campario and Chincha.

For the hibernation sites they prefer southern and south-eastern slopes near streams.

The hibernating areas are between 2,800 and 3,300 metres above sea level.

During sunny days thousands of butterflies will fly around the forest clearings.

In the winter sites most hibernate, i.e. stay in a deep sleep slowly consuming their reserves.

Some become active and feed on nectar and local flowers in order to recover lost energy.

They prefer to nest in the middle of trees where they are more protected from the weather and the temperature is more stable. They form large clumps to conserve heat and energy.

Sometimes adverse weather conditions such as high wind, heavy rain or snow causes thousands to die. When this happens the forest floor becomes an orange carpet.

Towards the end of February and until they migrate their principal activity is mating.

6. Migrating North

During March huge groups of butterflies rise up like clouds looking for air currents. They form huge orange rivers as they start north.

The females leave millions of eggs on their way north, mainly in the Central and South Eastern USA.

The caterpillars need milkweed to feed on. The availability of these sites is therefore imperative for their survival.

7. Predators and Self Defence

The caterpillar’s colour indicates to predators that it is toxic and has an unpleasant taste.

If eaten the toxins induce vomiting and a rapid rise in heart rate followed by cardiac arrest.

Although they are toxic to most animals some birds are immune to the toxins and thrive on them. There are two forest birds in the Reserves which eat them: Phecticus Melanocephalus and Icterus Galbula.