2020

Will there be a Painted Lady Butterfly Boom This Year?

With the start of warmer weather, we are lucky to spot many beautiful diurnal butterflies or the real butterflies more and more often. The richest family of diurnal butterflies in terms of the number of species is Vanessa cardui, which is commonly known as the painted lady. Latvia is home to almost sixty species of this butterfly family, which can also be found in the forest. Painted ladies feed mainly on the nectar of nectar fruit flowers, which means that they are pollinators.

Did you notice that last year, there were significantly more Vanessa cardui butterflies in Latvia than usual? Last year, for a few months in a row, they could be seen nearly everywhere. Wherever there were flowers blooming, they were there. It should be noted that this boom of Nymphalinae butterflies in Latvia was because of the strikingly massive presence of only one species of this butterfly family – the Vanessa cardui.

If you take a closer look at a painted lady butterfly, you will notice that it is difficult to mix it up with any other butterfly species, but at first glance, it may resemble a scarce tortoiseshell or large tortoiseshell, or a comma butterfly, but it most closely resembles the small tortoiseshell.

Vanessa cardui is not characterized by sex dimorphism; which means that males of this species do not differ externally from females.

Painted ladies are migrants

Vanessa cardui cannot resist cold. Even accidentally caught in the “clutches” of negative temperatures, adult members of this species die very soon, they are unable to hibernate in Latvia (and neither elsewhere in the relatively cool part of Europe). Therefore, this species migrates. Painted ladies make massive seasonal flights: in autumn from north to south, and in spring in the opposite direction. It is needless to explain why the first representatives of these insects never appear in Latvia in early spring, but are to be spotted much later, usually in May. They travel to us mainly from North Africa, the Canary Islands and the warm areas of Europe.

Vanessa cardui begin their spring movement from warmer countries to the north in March, April. Before migration, they gather in roosts. After flying hundreds or even thousands of kilometres, the first travellers usually reach Latvia already in May; however, the greatest parts of travellers arrive here only in June. The arrival of migrants continues also later in summer.

During their trip, most of Vanessa cardui suffer a lot; hitting along various obstacles and trying to pull away from the beaks of birds, the scales covering the body are shattered, and the wings are torn apart. As time goes on, the outlines of the wings of these insect become more and more dull.

The next generation – the “needled” larvae

When the specimens that arrived on time mate, a new generation of Vanessa cardui develops in Latvia. Butterflies reproduce only once in their lifetime. All adult males die eventually after mating and females after laying eggs. Their offspring – the “needled” larvae – can be seen here mainly in July.

Vanessa cardui larvae feed on the green parts of various herbaceous plants; however, thorny plants dominate their menu. Offspring of these insects are keen on different plants of Cynthia family, especially thistles.

The larvae eat, grow, reach a certain size and then they nestle their cocoons. At the end of summer, young butterflies hatch from larvae, which can then be observed in Latvia flying around flowers together with some of the old immigrants that have not died yet. The young specimens usually can be easily distinguished among the old ones, because their wings are still undamaged and very bright in colour.

In autumn, the new generation of Vanessa cardui gradually gather in roosts to leave – slowly moving further and further southwards. Their departure from Latvia takes place more actively in September. In 2019, the period of Vanessa cardui mass flight ended at the end of September, but the last specimens were to be seen here as late as in October.

Most butterflies spend two to three months on their way to the warm lands and arrive there in late autumn, when the vegetation for their future larvae grows generously in these areas.

The reproductive process does not stop: two or three generations change in the warm lands by the beginning of the spring migration. Each spring, the young southerners travel to colder countries, including Latvia.

The first bright-winged immigrants have already been spotted

The number of Vanessa cardui arriving in Latvia tends to fluctuate considerably from year to year.

The fact that they came to us in striking numbers last year means that a year before, adults of this species had good breeding conditions in the south, larvae had very favourable feeding conditions, and cocoons – favourable survival conditions. It is also possible that Vanessa cardui came to us in larger quantities than usual, because the conditions in Europe were especially suitable for their migration in the spring, for example, there was a long lasting tailwind.

This year, a number of natural processes were postponed in spring, some are still delayed. For the time being, there seems to be a bit of a delay in the mass arrival of Vanessa cardui. By the way, there are years when these insects do not come to us at all… However, this will not be the case this year, since some bright-winged immigrants have already been noticed in Latvia.