Lockdown: an opportunity to appreciate your local biodiversity

Garden studies during Covid-19…

Like all of us, I’ve spent the last few weeks confined more or less to my garden and the house. After a lifetime of reading dystopian science fiction novels like Stephen King’s ‘The Stand’ I never thought I’d end up living in a deadly global pandemic. And all the time at home has given me time to reflect. I have to admit I was struggling to come up with a subject for this issue of ‘Leopard’s Echo’. All sorts of ideas have been rattling around my mind since it became clear that my life might end sooner than I expected.

Even before the virus got loose, I was having more and more encounters with human indifference to the stresses our species puts on the other creatures with which we share this planet. As an admin on some large Facebook groups to do with insects in general and lepidoptera in particular, I was dismayed at the number of requests for ways to kill garden insects that were doing nothing but behaving naturally.

One Facebook group I admin for runs keyword warnings for ‘kill’, ‘control’, ‘eradicate’, ‘poison’ etc. We were getting into more and more ‘twars’ with gardeners who want a picture perfect, caterpillar-free, manicured garden. But these same people also wonder why they never see butterflies anymore, or why they don’t see as many birds as they used to.

The advent of Covid-19 comes at a time when we were already getting very concerned about human impact on biodiversity. The Amazon and Australian fires; Rhino poaching; the melting of the Greenland and Antarctica icecaps; the ‘insect apocalypse’ that has been reported on from places as far apart as Germany and Costa Rica. The list goes on and on. Have we as a species finally destroyed too much, and gone past some tipping points that we cannot recover from?

Perhaps a period of enforced close contact with local biodiversity might help people appreciate what they have around them.

It takes a period of ‘house arrest’ to appreciate biodiversity on a small scale

Our local Lepidopterists’ Society group decided to start keeping records of how many species we’d seen from our homes during the ‘lockdown’. I have to admit to being very lucky; I have a large garden that’s almost totally indigenous and attracts lots of butterflies. Iphithi Nature Reserve is just across the road. From 28 March to 30 April I recorded 65 butterfly species and several moths. At the time of writing this, 12 May, I’m on 71 species. My friend Mark Liptrot, whose garden borders on the Krantzkloof Nature Reserve, recorded 89 species during the main lockdown. However, many other people were keeping lists…

African Plain Tiger Danaus chrysippus orientis is a common butterfly in our area, and its larvae feed on Balloon Cottonbush, Gomphocarpus fruticosus. I was able to rear it from a larva I found on this plant, all the way through lockdown…

African Plain Tiger Danaus chrysippus orientis larva found on 15 April on Balloon Cottonbush. The butterfly above came from this larva.

LepiMAPping in lockdown

I had a suspicion that Citizen Scientists would have responded to the ‘house arrest’ by concentrating on their home ranges. I asked Prof. Les Underhill of the Biodiversity and Development Institute (the BDI) what he had found. I am grateful to Prof. Underhill for this detail:

‘By 10 May 2020, 2,267 KwaZulu-Natal records had been submitted to LepiMAP; all had been collected during the lockdown period 27 March to 10 May 2020. 18 LepiMAPpers had submitted records made in this period. They had visited 12 quarter degree grid cells. In contrast, during the same period in 2019 (ie. records made during 27 March 2019 to 10 May 2019 and submitted to LepiMAP at any time in the year up to 10 May 2020), 1,642 records were submitted. Records were submitted from 36 grid cells by 26 observers.

In 2019, 11 of the 26 observers (42%) had visited only one grid cell and the remaining 15 visited between two and five grid cells. In 2020, 15 of the 18 observers (83%) submitted from only one grid cell, where they were locked down. Two LepiMAPpers submitted from two adjacent grid cells. In each case one of the two grid cells has the bulk of the records. One LepiMAPper was able to submit from four grid cells. This citizen scientist lives far from the nearest town, so the records look like they were collected opportunistically on shopping/medical trips. Even so, the overwhelming bulk of the records were from the “home” grid cell.

This is summarised into this table:

The astonishing things: more records from fewer people in 2020 than in 2019 (more records will still arrive from other LepiMAPpers). The enormous decrease in coverage, from 36 grid cells to 12 (several LepiMAPpers live in the same grid cell).’

The same picture emerges nationally:

‘Here is the table with LepiMAP information for the periods 27 March to 11 May 2019 and 2020 for South Africa as a whole.

There an extra column. Last year each LepiMAPper submitting during the period visited 2.23 quarter degree grid cells; this year 1.16.

This reflects rather well on KZN’s LepiMAPpers… we spent most of our time at home. 18 of us – 20% of the South African total – 56% of the records!

I took advantage of the enforced home time to spend a lot of it walking around the garden keeping my eyes open. I watched out for larvae of interest, that could be reared for the Caterpillar Rearing Group…

This Emerald, Traminda neptunaria larva I found escaping down a silken thread from a bird party that was noisily investigating my Fever-tree Vachellia xanthophloea. I was able to capture it and rear it on leaves from the tree.

Adult Traminda neptunaria that emerged from a pupa formed inside a rickety-looking loose cocoon. I had been warned to expect a parasitoid, but I was lucky…

What can we do, as gardeners and nature-lovers?

This enforced holiday from human presence – fewer vehicles, less pollution, less noise – appears to have given nature a breathing space. I have heard many reports of the astonishing numbers of butterflies being seen in gardens around the country, and I know my birder friends have seen a similar phenomenon with birds. This has not only been noticed in our country, but in others as well.

8% of South Africa’s 1.22 million km2 land area, or just under 100 000 km2, falls under formal protected areas. Whether that is sufficient to preserve sufficient biodiversity is a matter of debate. I am not in possession of figures for the total area of our parks and gardens. However, a recent report stated that in the UK, parks and gardens cover a greater area than its nature reserves and protected areas. If that is the case in South Africa, then we gardeners have a wonderful opportunity to help protect our biodiversity.

But if we continue to do things that harm biodiversity, all we will do is hasten the day when the whole system collapses. Should this happen, our fate will be sealed. We’ve seen from Covid-19 that this type of ‘black swan’ event is possible. What will happen when insect numbers drop to zero?

So what can we do? Well, one thing we can do is to avoid pesticides and allow natural predator-prey relationships to develop.

• In nature, there are food chains.
• Every creature has an enemy that wants to eat it.
• There is a natural, well known relationship between prey and predator; basic to population dynamics as taught in Universities.
• If prey numbers become too large, predator numbers increase until the prey becomes fewer in number.
• If there is less prey, predator numbers will fall.
• Peaks in predator numbers usually occur after peaks in prey numbers.
• If you wipe out the predator… expect an explosion in prey numbers.

Let’s have a look at a couple of examples of predator-prey relationships in the garden…

Female Leopard Magpie moth Zerenopsis lepida on a cycad leaf with her egg mass – a sight to give many gardeners the ‘jitters’ and prompt them to reach for the can of ‘Doom’.

Photo: Luelle Watts.

Leopard Magpie Zerenopsis lepida larvae (cycad loopers) feeding on Encephalartos sp.

Photo: Lynette Rudman

A photograph of this moth on any Facebook page always attracts a lot of comments along the lines of ‘Blue Death works’ or ‘that thing killed my Cycad’. It’s true that its larvae are capable of destroying the fresh leaf growth on any Cycas or Encephalartos species, and this does not endear them to people who have spent a lot of money on these plants. It’s not the only species to feed on cycads. The tribe Diptychini of the subfamily Ennominae of the Geometridae (Looper Moths) all use these plants at some stage in their life cycles. Some only use them when young larvae, and change to other plants when older.

A year later the cycad shows no signs of lasting damage, and has put out a new flush of leaves

Photo: Lynette Rudman

Of course, the feeding damage of these larvae is unsightly to people who value a manicured garden. Using insecticides to wipe out the larvae may be tempting, but it can have unexpected side effects. Although birds and lizards feed on them, the most numerous natural enemies of butterflies and moths are arthropods – spiders and other insects. And of those other insects, the Hymenoptera – which comprises wasps, bees, ants etc – are the most numerous. Particularly wasps, of the superfamilies Chalcidoidea, Ichneumonoidea and Vespoidea.

The first two are known as parasitoids because they appear to be parasitic. They live inside their hosts as larvae, but because they eventually kill the hosts, they are not true parasites – hence ‘parasitoid’ – ‘similar to a parasite’. They have two different modi operandi. Idiobionts and koinobionts. Idiobionts paralyse their prey; the well-known Spider-killing wasps in the family Pompilidae use this method, but there are many idiobionts that use lepidopteran larvae, paralysing them and laying an egg inside the host. The newly-hatched wasp larva thus has a supply of fresh, living food. The host is slowly eaten alive from inside, the vital organs being left till last.

Female Pompilid wasp, Java caroliwaterhousi, with Rain Spider prey, Palystes superciliosus. Related to Velvet Ants, wasps of this family have the most painful stings of all wasps, containing powerful neurotoxins.

It that were not macabre enough for you, koinobionts do not immobilise their hosts, but live inside them whilst they feed and go about their lives. Eventually they also kill the host, bursting forth in a gruesome manner and spinning a cocoon on the (often still living) larva. Anyone who has seen the Alien movies will be familiar with a koinobiont parasitoid – the designer of the creature, HR Giger, based it on a mix of a parasitoid wasp and a dragonfly nymph. (*Pauses to shudder*).

Ichneumonoidea is one of the largest superfamilies in the Hymenoptera. The family Ichneumonidae is estimated to have about 100 000 species, of which only 25 000 are known to science. The other large family is Braconidae, which has 17 000 recognised species and may number nearly 45 000. As well as this, there is the superfamily Chalcidoidea, which is even bigger and less well-studied. Of the estimate 500 000 species only some 22 500 have been described to science.

Most are specialist predators of insects whose metamorphosis is ‘complete’ – four stages, egg, larva, pupa, adult. As such they are the main enemies and control mechanisms for butterflies and moths. A garden with healthy biodiversity will likely have thousands of these wasps, which are small and easily overlooked.

Female Charops spinitarsis wasp injecting Zerenopsis lepida larvae (the aforementioned Leopard Magpie moth) with eggs. Charops wasps are members of the family Ichneumonidae, and wasps like them are used in agriculture as biocontrol for many ‘pest’ lepidoptera.

Photo: Hermann Staude

Ichneumonoid wasps may look ferocious but that long ‘stinger’ won’t harm you. It DOES harm the caterpillars though. As well as injecting eggs that hatch into alien-like invaders, they also inject a venom that fools the caterpillar’s immune system into not killing the wasp larva. This contains a special virus – a polydnavirus – which is expressed by the wasp’s own genome. The virus causes other physiological effects that ultimately cause the parasitised host to die.

Cocoon of a wasp species in the same subfamily as Charops.

These small ‘Chinese lanterns’, about 3-10mm in size, are a familiar sight in local gardens.

Another lepidopteran that defoliates its host plant is the Boisduval’s Tree Nymph, Sevenia boisduvali boisduvali. The host plant is Sclerocroton integerrimus, or Duiker-berry Tree. It’s not a popular garden subject, which is probably a good thing because when the butterfly uses it, it uses it hard.

The normal lush foliage of Sclerocroton integerrimus.

Boisduval’s Tree nymph females go into an egg-laying frenzy on Sclerocroton integerrimus. Each batch numbers about 100 eggs and the life cycle is only about two weeks. Result – a food bonanza for the local predators, until the butterflies beat them with numbers!

Duiker-berry totally defoliated by Boisduval’s Tree Nymphs

The larvae hatch from the eggs and form these gregarious groups. They soon make short work of the foliage and eat everything they can find.

Wasps like this Polistes madiburensis move in on the butterfly larvae and either eat them Al Fresco, or chew them to feed to their own larvae.

Wasps in the superfamily Vespoidea are more ‘conventional’ predators of butterfly and moth larvae. This family includes the familiar hornets and paper wasps. Unlike Ichneumonoidea, these little devils can sting us. The adults catch larvae, and either eat them on the spot, or chew them up into a ‘bolus’ and put them into the larval cells in their nest. A good example is Polistes madiburensis, seen here chewing up a Boisduval’s Tree Nymph larva. To begin with the wasps take a terrible toll on the larvae, but eventually they are overwhelmed – for a while.

For a few weeks, the tree stands naked, with adult Tree Nymphs swarming around the surrounding forest. It can look like it is snowing butterflies. But slowly the birds and spiders take their toll, and no more larvae can develop because there is no more food left. Sometimes the adults migrate en masse away from where they were born.

All the time the butterflies have been breeding up, there are wasp nests all around, breeding up another brood of predators ready to feed off the butterflies’ offspring. These are Belonogaster wasps, in the same subfamily of the Vespidae as Polistes madiburensis.

The new broods of Polistine and other wasps are ready when the butterflies’ numbers start to increase again – and knock them back.

This is typical of the kind of predator-prey relationship that exists in all healthy biosystems. There are many of these – the wasps have their own predators, and I haven’t even mentioned all the other insects that prey on butterfly and moth larvae. There are flies that lay eggs on the host plant, and the caterpillar ingests these, which hatch inside it and eat it alive from the inside like the wasp larvae do. There are even microscopic chalcid wasps that parasitise butterfly eggs. The female wasp sits on the female butterfly’s ovipositor, popping one of its eggs into every egg the butterfly lays. So even it a butterfly lays hundreds of eggs, few may even make it to the caterpillar stage!

The lesson we can learn from all this is – there’s a reason why we seldom see massive plagues of single butterfly or moth species in the natural world. There are all sorts of feedback loops like the few I’ve described here, keeping numbers in check. Population explosions only occur when an extraneous event – such as a serious drought – or a misguided application of insecticide – wipes out the predators. We’ve seen the effects of droughts in the Kalahari – massive waves of Pioneer Caper Whites, Belenois aurota, migrating. The effects of unwise insecticide use may well be that eruption of Leopard Magpie moths among your monoculture of cycads…

So do yourself a favour and rewild your gardens…

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 Gardening for Butterflies. His app, Woodhall’s Butterflies of South Africa, is described as the definitive butterfly ID guide for South Africa.