Imagine you are going on a journey. The route you will take is one you have never travelled before, and it will take several lifetimes to get there. In fact, you will never arrive: only your grandchildren will see the destination, and only their grandchildren will finally arrive back at home. Between you, you and your progeny will cross an ocean and a desert, and your path will span the distance between the tropics and the arctic circle. You are very likely to be eaten. You may well join the 27 club, but in the 27th day of your life, not the 27th year. If this sounds daunting, be reassured of two things. You will have companions: on a good year, tens of millions of them. Beside this, you will be immortalised in literature.
Who are you? A Painted Lady butterfly (Vanessa cardui) – one of the species celebrated in Isabella Tree’s celebrated book Wilding. This May, Painted Ladies have been seen on Home Farm, Ambios’ rewilding site. This species is particularly good at helping us to see the world through an ecologist’s eyes, for a number of reasons.
Firstly, as with many butterflies, they have specific dietary requirements and a strong connection to a particular species of plant. Painted Lady caterpillars feed on Creeping Thistle, one of the first “weeds” to colonise the nutrient-rich soils of retired agricultural land. Isabella Tree relates how over the course of two years, swathes and swathes of Creeping Thistle covered a good portion of the estate she and her husband were trying to re-wild. In 2009, they were saved from this farmer’s nightmare by the arrival of a swarm of Painted Ladies that descended on the thistle and reduced it to rags.
Secondly, the number of Painted Ladies in the world can vary wildly from year to year. Normally arrivals to the UK number somewhere in the region of a million. In boom years however, such as 2009, it can be over ten times this many. What is a good year for butterflies is a bad year for Creeping Thistle, as females can lay about 500 eggs over their short lifespan, many of which will hatch into caterpillars that munch the thistle down. This army of invertebrates keeps the thistle in check. Such top-down, knock-on effects are known as “trophic cascades”. In the 21st century, ecologists are paying them increased attention.
Thirdly, as illustrated in the intro, Painted Lady butterflies are an example of a species whose migration cycle is longer than its lifespan. A caterpillar hatched in sub-Saharan Africa may metamorphose into an adult that flies a leg of the journey before landing in the Atlas Mountains of Morocco, there to lay eggs which will give rise to a new generation that takes on the next leg northwards into Europe. In this manner, some individuals may even make it as far as Iceland. A round trip from Africa to Europe and back takes about six generations. Painted ladies are also found in America where they make an equivalent multigenerational trip between Mexico and Canada. With a brain the size of a pinhead and no (known) way of passing knowledge on to their larvae, it is an enigma how they manage this feat. Research suggests that the butterflies navigate with the help of a solar compass found in their antennae. But how do they know what route to follow in the first place? We must assume that the journey is somehow encoded in their DNA.
So keep an eye out for this live-fast, die-young nomad next time you are out on a walk. The adults can be distinguished from the many other brown-and-orange butterflies at large in the fields by looking at the upper wingtips: you should see a constellation of white dots within a triangular black blob. Enjoy them while they’re here. In a month’s time they may be a thousand miles away.
✍Nick Trapp – Ambios Nature Conservation Trainee (Spring 2022)
???? Image by Adina Voicu from Pixabay
