All butterflies, however beautiful, have a caterpillar stage in their life cycle that involves the ingestion of plant material. That’s the bad news. The good news is that pretty much every butterfly and moth has specific plants that it lays its eggs on and that the larvae (caterpillars) will eat. So if you have caterpillars on your kale they are unlikely to eat your other garden plants.
In fact, to be honest, most caterpillars have evolved to eat wild or native plants in the UK such as nettles, because there are more of them than our overbred and alien garden plants. That said there is one type of caterpillar that most gardeners dread; the cabbage white. It’s not correctly called a cabbage white, but because its favourite host plant for laying eggs are cabbages and because the adults are white, it has acquired this name.
Cabbage white butterflies are still butterflies and great garden pollinators. Remember that butterflies of all types make up the complex tapestry of nature and have a place in the fragile food chain.
The second batch of bad news is that there are two types of cabbage white and the chances are you have both in your garden. There is a large white (Pieris brassicae) and a small white (Pieris rapae). To make matters worse there is also a cabbage moth (Mamestra brassicae) and although they prefer cabbages and other members of the Brassica family like broccoli, kale and sprouts, they are also very partial to nasturtiums too.
In essence their lifecycle is the same as most other butterflies and moths, the adults mate and lay eggs on their host plants. The eggs hatch out and it is the emerging caterpillars and their voracious appetite that does the most damage to the plants as they feed and feed and feed until they are ready to pupate. The adult butterflies will emerge the following spring to mate and complete the lifecycle.
- Cover susceptible plants with fleece or netting to prevent access by adult butterflies so that they cannot lay eggs on your plants. Check regularly and make sure that the plants beneath are not touching the netting.
- Check the leaves of your plants for the tell tale signs of caterpillar eggs. It’s pretty unlikely other species of butterflies will lay eggs on your plants, but never guaranteed. The cabbage whites have pale golden yellow eggs. Pick off affected leaves, with the eggs.
- If your plants are covered in caterpillars, try to remove them manually, or wash them off with a hose. Grow a few magnet plants on the periphery if your plot and allow the eggs and caterpillars to develop here instead. These are a great place to watch the natural process and observe how the plants deal with pest attack. Even though they may have severe leaf damage, plants are unlikely to die and you may be surprised how well they ‘cope’.
- If you must spray your plants remember that it is essential to read the label especially if you plan to eat the treated plants after spraying. Where possible choose a product approved for organic gardening that is based on natural compounds such as pyrethrum, but don’t be fooled, these are still very powerful, toxic chemicals that can affect a range of insects including bees. Follow the instructions very carefully and do not spray on open flowers.