Eileen Tiller, of Paraparaumu, asks :-

Do butterflies have memories? I notice that monarch butterflies hover over the exact spot in my garden where a swan plant used to grow.

Samantha Botting, a zoologist in charge of the Tropical Forest at Otago Museum, responded.

I can assure you that they do.

In 2008 a study was done in America which proved that butterflies remember things they learn as a caterpillar. They revealed that caterpillars which learned to avoid certain odours (as they got an electric shock if they crawled into areas which had the odour) retained this learned behaviour to the same odours when they emerged as a butterfly.

Therefore, if the monarchs in your garden were caterpillars on the swan plants that were there it is feasible they remember the plants location.

However, a monarch’s life cycle on average from egg to butterfly is between 5-9 weeks and they spend 2-4 weeks as a butterfly. Consequently, if your swan plants have been absent from your garden for longer there are must be other reasons than memory as to why they are hanging around.

One reason could be that monarchs are known to migrate extraordinary lengths. There is not much data on their migrations in New Zealand, however, there is some on American populations’. In September millions of monarchs begin a yearlong, 3-5 generation, migration from North America, through Texas and as far as the Gulf of Mexico. The whole migration spans over 4000kms and the butterflies that make it home are the grandchildren, or the great-grandchildren, or the great-great-grandchildren of the monarchs which left a year earlier. This relates to your scenario because the descendant monarchs are known to return to the exact same plant which their ancestors flew off from at the start of the migration. So potentially, you were witnessing migrating monarchs’ trying to find a swan plant which they were born with an innate ability find.