Does climate change affect butterflies and moths?

Why would climate change affect butterflies and moths?

Butterflies and moths, being insects, are cold-blooded, and their levels of activity are affected by temperature. They adapt to specific climatic conditions and their distribution patterns reflect this. So as the climate becomes warmer it might be expected that hot country species from further north in Africa might start to invade our area. For at least one species, this appears to be the case.

Forest Queen Charaxes wakefieldi is a butterfly of coastal and lowland forests in Eastern Africa. It used to be very rare in KwaZulu-Natal, only being found regularly in northern forests, and then seldom seen. This is a male, a mimic of the Blue Monarch Tirumala petiverana, which is almost never seen in South Africa.

The female Forest Queen mimics the much commoner (in KwaZulu-Natal) Friar Amauris niavius dominicanus. It’s easy to mistake for that butterfly as it soars across the forest canopy.

For many years the southern limit of this butterfly was Scottburgh, and then only from two records from the 1930s. Since 2005 there have been over 70 records made from the same quarter-degree grid square – now going as far south as Bazley Beach. It is commonly seen in Durban suburbs such as Bluff. Its caterpillar feeds on the common Dune Soapberry Deinbollia oblongifolia, which has a more southerly distribution too.

Another butterfly whose range has expanded widely to the south is the Sabine Albatross White, Appias sabina phoebe. Until the 1980’s it was known as mainly a northern species from eastern Zimbabwe and Mozambique. In South Africa it was confined to the foothills of the Wolkberg – Magoebaskloof and Legalameetse – where it was found in warm, sheltered subtropical forests. There were a couple of records from Dukuduku forest near Mtubatuba in the 1970’s.

Sabine Albatross White (this is a female) has, since the 1980’s, spread across the whole of the coastal side of KwaZulu-Natal and has reached the Eastern Cape (Port St. Johns). It has been recorded in Krantzkloof Nature Reserve. Like the Forest Queen, its host plant is a common forest tree – in this case Drypetes gerrardii – and the warmer conditions of recent years appear to have helped it expand its range where the larval food is available.

Other effects of climate change

As the climate changes, so do the seasons. This next part is based on my own observations and as such could be challenged by professional climatologists. When I first moved to Chelmsfordville in 2005, August was a dry and windy month and heavy rains occurred in late August and early September. There was then a dry spell that lasted until December, during which we saw a lot of butterflies. Then more rains in February and early March, followed by a dry April and May, again with lots of butterflies.

In the past 5 years, the dry windy weather seems to stretch into November and December. Then we have had very wet January and February weather, stretching into March. Most butterflies are not active in rainy weather; they are reluctant to fly, affecting their ability to mate. This reduces breeding success and hence numbers. And the dry spring weather (or actual droughts) also adversely affect butterfly numbers.

This male Mother-of-Pearl, Protogoniomorpha parhassus was photographed perching in Glenholm Nature Reserve in August 2014. They were a common sight in my Chelmsfordville garden at that time of year, but in recent years (since 2016) I seldom see them in August. They appear in March and April but not in the numbers they used to be seen.

Butterflies like the Common Mother-of-Pearl, and the Gaudy Commodore Precis octavia sesamus, are known to overwinter as adults. Gaudy Commodore numbers are also down compared to the pre-2016 period. Could it be that wet summers and autumns are damping down the peak of emergence that used to increase the numbers that overwinter and appear in early Spring?

We must remember that the whole of KwaZulu-Natal was gripped by drought in 2015-16 and this has only really been broken in the southern coastal areas. This undoubtedly had an effect. But would it persist through several subsequent seasons with good rains?

There is reason for hope. After an absence following the drought of 2015-16, one autumn forest butterfly that used to be found in Giba Gorge, as well as the Mpiti Trail in Krantzkloof, and my garden (of which I am inordinately proud) reappeared in 2018 and seems to be having a good 2019.

One butterfly that disappeared from my garden after the 2015-16 drought was the Lowland Bush Beauty. It seems to have recovered. This photograph was taken in early April.

Effects of extreme weather events

Heavy wind and rain

Cyclones, devastating storms and even tornadoes are not unknown for our area. In the UK I well remember seeing British Swallowtails Papilio machaon britannicus in good numbers one weekend, then after a big thunderstorm… nothing. But I suspect our African butterflies are made of sterner stuff.

An example of a butterfly that can withstand a cyclone. I visited the old Natal province just after it had been hit by Cyclone Domoina in 1984. I stayed in Scottburgh and during the weakly sunny weather immediately afterwards, found a female specimen of Satyr Charaxes, Charaxes ethalion ethalion, in a nearby forest. (it wasn’t this one!) Other common coastal butterflies were already out.

Drought

As already mentioned, the drought of 2015-16 had a big effect on the butterflies found in Kloof. We appear to be fortunate in that the vegetation seems to bounce back, and butterflies reappear. This may be due to the presence of cool, damp, sheltered valleys where drought-sensitive species can take refuge. Krantzkloof Nature Reserve has several such valleys.

This makes it even more important that the reserve, and others like it. continue to be preserved and managed well. A rare Charaxes butterfly, which is normally only found at higher, cooler altitudes, is found in such valleys. Should it disappear, that could be a sign of catastrophic warming in Krantzkloof.

Karkloof Charaxes. Charaxes karkloof karkloof, is normally found in the cooler, higher altitude Afromontane forests of the KwaZulu-Natal Midlands. They can be found flying along the wooded streams in Krantzkloof Nature Reserve, and their larvae can be found feeding on their host plant Cape plane Ochna arborea in the shade of the canopy along these streams. Nkutu Falls is a good place to look for them.

This Karkloof Charaxes caterpillar is feeding on a Cape plane Ochna arborea along the stream lading to Nkutu Falls.

So is climate change affecting our butterflies?

The evidence is strong that some species are following the warmer climate south. A number of species appear to have expanded their range. But we must beware of making assumptions. The recent explosion in popularity of Citizen Science projects such as LepiMAP may be having an ‘observer effect’; they may well have been present all the time, but people just weren’t noticing.

Hypochrosis meridionalis was, until a recent Kloof Conservancy-LepSoc Africa ‘moth night’, only known to be found as far south as eastern Zimbabwe. It caused a sensation amongst local lepidopterists when it was found in Krantzkloof. This is a nocturnal species confined to heavily forested hills. Has it been quietly spreading south, or was it in our area and not seen until we were ‘in the right place at the right time’?

Fluctuations in butterfly and moth numbers may be a result of climate change, or do other factors play a role? Pesticide use by gardeners and farmers may be affecting populations. Another possible cause is urbanisation and development, destroying suitable habitat.

No matter what the cause, it’s important that we continue to cherish and protect the areas of natural habitat under our care. Wild and undeveloped areas such as we have around Durban are precious, but so are our parks, and gardens – as long as we plant locally indigenous and eschew the use of pesticides!

Steve Woodhall is a butterfly enthusiast and photographer who began watching and collecting butterflies at an early age. He was President of the Lepidopterists’ Society of Africa for eight years, and has contributed to and authored several books, including Field Guide to Butterflies of South Africa and the popular What’s that Butterfly? His app, Woodhall’s Butterflies of South Africa, is described as the definitive butterfly ID guide for South Africa.