Citrus Caterpillars: Are Swallowtail Caterpillars Really A Problem?

If you love growing your own citrus trees at home, you’ll know how important it is to keep your citrus happy and healthy. Healthy trees are attractive in the garden and are more likely to reward us with a crop of delicious citrus fruits. Controlling pests is a key part of this. Find out what you should you do if you discover citrus caterpillars on your trees and more about the butterflies that they turn into.

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Caterpillars on your citrus trees

Gardeners who grow lemons, limes, oranges or other citrus at home know that we need to inspect our trees regularly for signs of pests or diseases. Whether you grow citrus in the ground or in pots, there’s a good chance that you’ll eventually notice the tell tale signs of caterpillars.

Usually you won’t notice the butterfly eggs hiding on the leaves. But once they hatch and the young caterpillars start to eat, the chewed leaves become more obvious. As do the culprits, which are usually the citrus-loving caterpillars of swallowtail butterflies.

Types of swallowtail butterflies

Depending on where you live, you may encounter different types of swallowtail butterflies. There are over 550 species of swallowtails around the world. Of these there are some sub-families where the caterpillars particularly like to feed on citrus trees.

Some of the many swallowtail butterflies that you might find laying eggs on your citrus trees include these species in:

• the USA – the lime swallowtail, lemon butterfly, or chequered swallowtail (Papilio demoleus), and the giant swallowtail (Papilo Cresphontes)
• Australia – the dainty swallowtail (Papilio anactus) and orchard swallowtail (Papilio aegeus)
• Asia – the Asian swallowtail (Papilio xuthus)
• Sub-Saharan Africa and the Arabian Peninsular – the citrus swallowtail (Papilio demodocus).

How to recognise swallowtail caterpillars

Swallowtail caterpillars come in a range of colours like bright green, brown and black, but have some similar features. They often have brightly coloured warning spots or stripes, and soft protective spikes along their bodies. Others are brown and look a bit like a bird dropping or a slug.

If disturbed, swallowtail caterpillars rear up and a brightly coloured red or orange forked defensive organ called an osmeterium emerges from behind the head. Dainty swallowtail caterpillars have an orange one. This organ secretes a smelly irritating acid to warn off predators.

These caterpillars are from beautiful butterflies with similar features. The butterflies are usually black with white or yellow markings, often spotted, and can have colourful orange, red or even blue patches on their lower wings.

The beautiful dainty swallowtail butterflies in our garden at home have spots of red.

Lifecyle of swallowtail butterflies

Swallowtail butterflies lay quite large, spherical pale yellow eggs on the upper surface of new citrus leaves. After 3 to 4 days these will hatch into small dark caterpillars. The caterpillars go through 5 to 6 stages of growth and shedding of their exoskeleton (called instars). Growing caterpillars feed on the citrus leaves, starting with the new shoots and moving on to more developed new green leaves.

When fully mature, the swallowtail caterpillar is about 35 mm (1.4 inches) long. It then pupates, with the well disguised pupa attaching to the stem of the tree. The dainty swallowtail pupa on our trees are usually a green-brown colour that blends perfectly with citrus branches. Others are bright green and look very much like leaves. The pupa is attached to the tree with a fine silk ‘girdle’.

After 2 to 4 weeks (depending on the season and how warm it is), the mature butterfly emerges from the pupa. The butterfly dries its wings and then flies off to start the cycle again.

How to deal with citrus caterpillars

The caterpillars from citrus loving swallowtail butterflies love to feed on citrus trees and some other native trees in the same family (including Australian finger limes). They prefer the new growth, and can do a reasonable amount of damage if there are lots of caterpillars on one tree. So what should you do about them?

Leave them be

Butterflies are important pollinators and are really beneficial to have in your garden. They are also beautiful. With smaller gardens and less flowering plants available to feed on, butterflies are struggling in many places. If your citrus tree is established and can handle some chewed leaves, ideally let citrus caterpillars be. Your garden will thank you.

Newer trees can be a bit more problematic. We recently discovered not one but 8 dainty swallowtail butterfly caterpillars on my newly planted potted blood orange tree. With such a small tree, the caterpillars were doing quite a lot of damage.

Remove and relocate

You may not be prepared to go these lengths, but my nature loving family actually removed the caterpillars from the tree to care for them. We kept them in a container and fed them on fresh citrus leaves from our more established trees for a week until they formed their pupa. And after about 2 weeks, they hatched and we released them one by one back into our garden. An easier alternative would be to simply relocate them to more established citrus trees to start with.

If you really want your citrus caterpillars gone, I highly recommend picking them off your tree by hand instead of using any sort of insecticide. Spraying can harm other beneficial insects.

More Tips For Growing Citrus At Home

Caterpillars aren’t the only pests you’ll find on your citrus trees. Find out about other common citrus pests like citrus leafminer, citrus gall wasp, citrus bud mites and scale insects. Or learn more about how to care for citrus trees in Autumn/fall.

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