Happy World Swallowtail Day! 9 June 2019

Monika Böhm

There are just over 550 species of swallowtails worldwide – the flamboyant rockstars of the butterfly world.

Including the largest butterfly in the world, the Queen Alexandra’s swallowtail, this insect group has captured the imagination of collectors and naturalists across time. But why celebrate this group on a specific day? And how is ZSL including swallowtails in their day to day work?

June 9th is World Swallowtail Day! Swallowtails are magnificent creatures – colourful, with often beautiful swallow tails (hence the name) and many of them quite big for butterflies, they have been the prized possession for many collectors over the centuries. But they are also affected by habitat loss around the world: loss of forest and caterpillar food plants, use of pesticides, climate change and invasive species can have severe impacts on swallowtails too, and are probably the most pervasive threats at present to this species group.

Tropical Swallowtail
See tropical swallowtails up-close at ZSL London Zoo's Butterfly Paradise

Researchers in ZSL’s Institute of Zoology are currently assessing the status of the world’s swallowtails, by carrying out a full comprehensive assessment of their extinction risk for the IUCN Red List of Threatened Species – an exercise that was last carried out in 1985! So this status assessment is long overdue. So far, we have published assessments for 80 species on the Red List, including the large birdwing butterflies – charismatic invertebrates with a wingspan of 25 -30 cm in the case of the Queen Alexandra’s birdwing. And we of course haven’t stopped there – a team of dedicated volunteers are helping us with drafting of the status assessments for the remainder of this species group.

Of the 179 species so far assessed, 20 species have been assessed as threatened, though so far none in the highest threat category of Critically Endangered. That’s 11% of the species assessed. The same proportion was assessed as Near Threatened, while nearly three quarters, or 130 species, were assessed as Least Concern. Only nine species have so far been assessed as Data Deficient.

Here are some of their stories:

Wallace’s Golden Birdwing, Ornithoptera croesus, is a member of the magnificent birdwing group of swallowtails. Alfred Russel Wallace named this species in 1859 and dedicated a passage of his book “The Malay Archipelago” to this remarkable species: “The beauty and brilliancy of this insect are indescribable, and none but a naturalist can understand the intense excitement I experienced when I at length captured it. On taking it out of my net and opening the glorious wings, my heart began to beat violently, the blood rushed to my head, and I felt much more like fainting than I have done when in apprehension of immediate death. I had a headache the rest of the day, so great was the excitement produced by what will appear to most people a very inadequate cause.” The species has just been reassessed as Near Threatened.

Queen Alexandra Swallowtail
The Queen Alexandra swallowtail is the largest butterfly in the world

The Queen Alexandra’s birdwing, Ornithoptera alexandrae, the largest butterfly in the world, has been reassessed as Endangered. The species only occurs in a small area in eastern Papua New Guinea and is threatened by habitat loss for oil palm plantations. Given its sheer size, some people have described it as a dinner plate flying around your head.

Baronia brevicornis (or the short-horned baronia), is a species from Mexico, which is particularly interesting since it is regarded as one of the basal species of swallowtails, a swallowtail prototype so to speak. It has been assessed as Endangered, as it occurs over a relatively small area in Mexico and requires a specific food plant for its caterpillar to feed on, a species of Acacia. If that was not specific enough, research suggests that they prefer very mature trees and areas with a relatively high density of the food plant present, so habitat loss and especially loss of mature plants is a major problem for this species.

UK Swallowtail
Some swallowtails can be spotted in East Anglia, England

Papilio machaon is the swallowtail we also get here in the United Kingdom, in East Anglia. While the species is widespread in the Palearctic region, the UK has its own endemic subspecies and this is becoming increasingly rare. It is the UK’s largest butterfly with a wingspan of 9 cm, and is now confined to the Norfolk Broads. These fenlands are potentially at risk from sea-level rise and salinisation which would destroy the foodplant Milk Parsley, Peucedanum palustre.

To highlight the plight of these and other species of swallowtails on World Swallowtail Day, we have released a special episode of ZSL’s WildScience podcast. Hear about the amazing species and their conservation needs from around the world, their bird poo mimicking larvae and get a good (metaphorical) sniff of the osmeterium. And we hear from Mark Collins of the Swallowtail and Birdwing Butterfly Trust, the brains behind World Swallowtail Day, about their amazing conservation work in Indonesia, Papua New Guinea, Jamaica, and even our very own doorstep, Norfolk – to name just a few of their projects!

Swallowtail caterpillar osmeteria
ZSL London Zoo's Butterfly Paradise design is based on a swallowatil caterpillar, featuring it's vibrant osmeteria at the door opening

Here at ZSL, we will work hard on completing the assessment of the world’s swallowtails by 2020. This is a very time-consuming and pain-staking job, and wouldn’t be possible without the help of many people who give their time freely to help. So as Volunteers Week comes to a close, here’s a quick shout out to all the volunteers helping on this project. Without your help, we would not be able to run assessments like these. So a massive thank you to everybody involved! And thank you to our friends from the Swallowtail and Birdwing Butterfly Trust for instigating World Swallowtail Day. Now let’s go and celebrate these magnificent insects! Happy Swallowtail Day!

Download the podcast

See swallowtails at ZSL London Zoo's Butterfly Paradise
 

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