A swallowtail caterpillar on a leaf

Spotlight: citrus swallowtail

It looks like bird droppings on a leaf, but don't be fooled: it's a caterpillar in disguise.

This seemingly innocent creature causes devastation in some agricultural communities, eating young citrus trees and destroying nurseries.

It is capable of rapid population growth and it moves into new countries quickly, making it a serious potential threat to farmers.

And it gets away with resting on leaves, right underneath a predator's nose, thanks to a clever costume.

Black and white stripes combined with a knobbly body make the caterpillar look remarkably like bird droppings.

This unappetising outfit is a clever ploy to hide in plain sight, a trick used by several swallowtail butterflies in the Museum's Sensational Butterflies exhibition.

You'll have to look carefully to find them, but the tiny creatures can usually be found on top of leaves, quietly confident they won't be recognised.

Swallowtail caterpillars are green once they grow large

Swallowtail caterpillars are green once they grow large

 

Kerry Calloway, who helps manage the tropical butterfly house, says, 'When they are resting on top of a green leaf, they look just like bird droppings.

'It protects against some of their biggest predators, because birds will overlook them, not bothering with something that does not looks edible or alive.'

Unappetising disguises

The newly-hatched caterpillar, dark and glossy with white markings, stays in the middle of the upperside of the leaf.

A disguise this good helps it to remain safe while feeding or moving around.

Once it gets bigger and fades into a pale green colour, the caterpillar must be more careful, staying in secluded places.

Kerry says, 'Caterpillars can only get away with this trick while they are quite small. When they grow bigger, they turn green and blend in among leaves.

'A defence reflex also helps at this stage: when they are touched they arch their backs and send two red horns protruding from their heads.

'A foul smell is released at the same time, warning predators away.'

Economic significance

Several swallowtail species have adopted this unsavoury camouflage for their caterpillars, including the striking citrus swallowtail (Papilio demoleus).

The citrus swallowtail is widespread in several areas, including the Caribbean and southern Asia, and it has been seen in savannahs, gardens, and evergreen forests.

Citrus swallowtail

The citrus swallowtail is considered a pest in some countries, where its caterpillars can destroy crops

 

Also called the common lime, the butterfly is a considered a pest in many countries, due to the destruction its caterpillars can cause.

Citrus is vital to agriculture in several countries, contributing to individual incomes, employment, food security and economic growth throughout the Caribbean.

But the plant is already in decline in several countries because of diseases and pests, including the citrus swallowtail.

The citrus swallowtail's tolerance of diverse environments has been key to its success across the globe - often at the cost of farming and agriculture.

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