If you're a keen vegetable gardener, you will most definitely recognise the black-spotted yellow caterpillars chomping away at your cabbage and kale crops. This is the caterpillar of the Cabbage white butterfly, Pieris brassicae, and although the white fluttering butterfly is a beautiful sight in the garden, the caterpillars can cause quite a bit of destruction to your vegetable patch.
Pieris brassicae is widespread in Europe and in some parts of Asia and was introduced into South Africa from Europe. The butterfly has settled in the Western Cape
Female butterflies lay yellow bottle-shaped eggs in clusters of 40-100 on Brassica crops. Prior to hatching, the yellow eggs turn bright orange. When the hairy, black-spotted yellow caterpillars emerge they feed in groups, gnawing the surface of the leaves.
Photo by @NatsGard3n
As the caterpillars mature, they feed in smaller groups (4-6 individuals) and eventually feed individually. These little guys can turn lush leaves into skeletons in just a few days.
One would think these clusters of young caterpillars are a buffet for birds, however, birds tend to avoid them due to the distasteful mustard oils the caterpillars obtain through the host plants.
Photo by @NatsGard3n
Caterpillars mature between 26-29 days, after which they pupate as a chrysalis on a plant or on walls or other structures. Butterflies emerge from the chrysalis with their beautiful grey-dusted white wings, in search of food and the perfect food source for the next generation. There are usually 2-3 generations per year.
Lifecycle of the Cabbage white. Photos by @NatsGard3n and @ArneStander.
The butterflies are attracted to blue and purple flowers and can commonly be seen on Salvias, Buddlejas and Lavender.
Community gardener @NatsGard3n started a very exciting experiment about two weeks ago. After discovering a cluster of the yellow eggs on her cauliflower, curiosity kicked in and Natalie decided to leave a few eggs on one leaf on one cauliflower plant to see what happens.
"We can only enjoy the butterflies if we allow some caterpillars." - Natalie
After the eggs hatched, the caterpillars started chewing their way to maturity. Currently, on day 15, there are now about 130 caterpillars, measuring roughly 15mm.
If you're 'eggspectant' to see how the experiment plays out be sure to give @NatsGard3n a follow or check out the posts below.
If you are not too keen on donating a plant or two to these caterpillars, entomologist @ArneStander lists a few preventative measures to protect your Brassica crops from being devoured, below.
How do I get rid of them?
- Management includes the planting of nasturtiums (Tropaeolum majus) near cabbages, as caterpillars also target them. This can help with monitoring and control strategies.
- Small developing cabbage plants should be protected, as they are more affected compared to more mature plants.
- Nets can be used to cover the younger cabbages - this will prevent adult female butterflies from scattering their eggs on the surfaces of leaves.
- Inspect your crops regularly. The young caterpillars that feed as a group are easier to remove than the more mature caterpillars which feed individually. You can simply hand-pick them and kill them or throw them in a container filled with water. A few drops of dishwashing liquid also reduces the water surface tension and will allow caterpillars to sink and drown.
- Natural enemies of the caterpillars include parasitoid wasps such as Pteromalus puparum (Pteromalidae) and Apanteles sp. (Braconidae).