Insects on the move

Smaller, vaster, better, faster

Insects migrate. In a GRAND way. Forget the migration of the wildebeest across the Serengeti. The painted lady butterfly, found all over the world, migrates from as far North as the arctic circle to the tropics and back – a 14 000 round trip. Individuals fly several thousand kilometres! Dragonflies migrate between India and Africa, flying several kilometres up in the air, over open ocean. How is this even possible? The mind boggles.

In my opinion humans always underestimate insects. Because they are small we don’t take them seriously, we don’t appreciate them, we don’t give them the respect they deserve. Even when we are finally made aware of some amazing feat, we are still missing something even more amazing.

The vagrant emperor dragonfly, also featured in the header, is a known migrant. It is a spectacular animal, one of the largest dragonflies that exists. It occurs in Durban – this individual strayed into our house.

The painted lady butterfly completes its migration over the course of a few generations. The offspring can’t learn the route from their parents. So how do they know to stop flying South, but turn around and head back North? This is a mystery worth solving!

Because they are so small, insects mostly move about in secret – at least from us. And yet, migrating insects such as butterflies, can travel in such vast numbers, that their swarms register as weather systems on radar. In America, mayfly swarms have been mistaken for major storms. Mayflies are totally harmless (adults don’t eat anything), they are short-lived (they live just long enough to mate and lay eggs, i.e. hours, or a day or two at most), and they are hugely important ecologically. Their larvae, which feed on algae and detritus, take up to several years to grow up, and are food for freshwater fish. Think about it: they turn detritus into fish food (and ultimately food for us). They tend to live in relatively clean water, as such they are considered indicator species (a litmus of environmental health).

This mayfly hatched from a streamlet that flows through our property in Pinetown. I hope that means the water is clean!

Mayfly nymphs – of both sexes, and various sizes – in a shallow stream near Bazley Beach. The perfect fish food!

This mayflies swarm emerged on a warm day in early spring, in the Eston area.

Every so often we read in the news about spectacular cicada swarms emerging. Some broods of periodic cicadas emerge like clock-work, every so many years. For example, every 13 or every 17 years, larvae taking exactly that long to mature. Not 12, nor 16, and not 18 either, but good solid prime numbers. “The philosophy is that if cicadas have 12-year cycles, all the predators with two, three, four, and six-year cycles will eat them.” Large prime numbers are a safe bet. Periodic cicadas provide massive periodic influx of food and soil nutrients.

A beautifully camouflaged cicada resting on a tree, in Pinetown.

Nature’s pest control services

Ladybug swarms can also trigger a weather radar. A massive ladybug swarm appeared like a massive storm cloud, 130km across. There was no rain, only what we can assume were billions of cute, red beetles. Many ladybug species – both adults and larvae – eat aphids, scale insects and other plant pests. They provide an invaluable pest control service in agriculture (as long as crops are not sprayed with insecticides).

Ladybird beetles come in such a lovely range of bright colours and bold patterns.

Ladybird beetle larvae also eat aphids.

Billions of hoverflies cross the English channel, every year. Like ladybugs, hoverfly larvae eat aphids, thus providing invaluable pest control services in agriculture (as long as crops are not sprayed with insecticides). The adults feed on nectar, providing invaluable pollination services (as long as crops are not sprayed with insecticides). Sorry to repeat myself.

A hoverfly on my rose bush.

Hoverfly larvae helping me protect my roses. I never use insecticides for that very reason.

Problems and plagues

Invasive pest species are often introduced by humans (usually accidentally). The fall armyworm, originally from Central America, has invaded much of the world over the course of six years. This frightening pest caterpillar has a wide diet range. It happily eats all of our staple crops, plus 100 other plants from many different families – basically, anything. The adults are strong fliers. They spread far and wide, using winds to help them along. Even in Brazil (their home turf) fall armyworm control operations exceed 600 million dollars every year. The indigenous African armyworm is not joke either. It can devastate harvests in record time, triggering emergencies across the continent. Amazingly, even the caterpillars ‘migrate’, which is how armyworms got their name in the first place.

African armyworms on the march

Photo by ChriKo

Another swarming, migrating pest we all know of is the African locust. Right now, as we speak, a locust plague of Biblical proportions is still underway. It has been the worst in living memory for many people. It was kicked off in 2018 by two cyclones that made landfall in Yemen, forming lakes in the desert. This set off a devastating chain of events. Locusts emerged in great numbers, and started to spread across the Arabian peninsula, from there to Iran, Pakistan, India, as well as to East Africa. Further cyclones, fanned by climate change, brought unusual rain to the normally dry Horn of Africa, which fuelled further generations of hoppers. The current ‘upsurge’ has already destroyed hundreds of thousands of hectares of crops and pastures. Millions of people are facing famine and risk of starvation, plus a deadly pandemic, on top of existing, chronic, multidimensional poverty, as well as ongoing civil unrest and war in some areas. The heart cries.

The green milkweed locusts are highly gregarious, and are capable of migratory flights. However, they do so as individuals, not as swarms. This band of hoppers was spotted in Paradise Valley.

Having mentioned insecticides and their role in killing off useful insects, I ought now to consider this in the light of the fact that agricultural pests cause about a 40% reduction in the world’s crop yields. As valuable as they are, insects can also cause havoc. In desperation we turn to insecticides. However, insecticides have a limited ‘shelf life’ as pests easily develop resistance to these chemicals. Some pests are resistant to every insecticide on the market. Suffice it to say that research is ongoing, on how to control pests without creating other health and environmental problems and killing off all the beneficial insects and pollinators in the process.

Harlequin ladybird beetles have been reared as biocontrol agents to help control agricultural pests. Unfortunately this beetle is now itself an invasive species, that feeds on and threatens non-pest species and even indigenous ladybirds. It is extremely variable, from yellow to red, from solid colour to all-black, two dots to 20 or more, black with red dots, red with black dots… It can be identified by the bold white patches (and the black “M” shape) on its ‘pronotum’ – the shield behind the head.

All hail insects!

Talking about pollination, one thing worth mentioning is human-assisted insect migrations, that is, migratory beekeeping. Every year American beekeepers truck thousands of hives from one corner of the USA to the other, to supply essential pollination services to almond, apple and blueberry farmers, and others. The food production system is too intensive, and too concentrated in time (boom and bust) for local pollinators to meet the needs of agriculture.

Covered in fine fur, a bee makes the perfect pollen duster.

Apart from working hard for all and sundry, insects end up as food (and thus poop) of spiders and birds and other animals. Insects themselves poop. Insects die. In every way they fertilise the land, by boosting nitrogen content and fungal activity. When insects migrate, they transport tons of biomass, as well as valuable nutrients, like nitrogen and phosphorus, from one area to another. This massive redistribution of biomass makes a significant contribution to ecosystem health and plant growth. This is the sort of thing we have completely undervalued and tend to be ignorant about – myself included.

General insect swarming happens for the purpose of mass mating (safety in numbers). But actual spatial migrations tend to follow the availability of food. The dragonfly migrations that Steve Woodall wrote about, from India, via the Seychelles and Comoros, to East Africa and back, follow the monsoon rains, and thus the availability of water for their larvae, and the availability of other insects for food. Ladybug and butterfly migrations, also move back and forth across the land with the coming and going of the seasons.

The orange-winged dropwing dragonfly is not a regular migrant, but has recently expanded its range into Southern Europe from Africa, probably due to climate change.

By spreading far and wide, insects ‘hedge their bets’: as soon as food becomes available somewhere, sometime, somehow, immediately they arrive and take advantage of it. Neil Crouch (the plant hunter) once told me that very soon after planting a Zimbabwean tree in his garden he spotted a species of butterfly whose caterpillars are known to feed exclusively on this plant. How did this butterfly get here? Where did it come from? How did it find this tree in this place? So quickly?

This is truly amazing, and gives me great hope when it comes to nature restoration. The moment we replant indigenous trees, or remove the aliens to allow local flora to flourish, the moment we leave nature to do what nature does best, nature does the rest. In no time at all the insect return, with all their services, filling the gaps in the food web, allowing birds and reptiles to flourish likewise. Insects are our biggest allies in so many ways. I wish people could appreciate this, and not freak out when a few caterpillars are cheeky enough to eat a flower planted in the garden. Insects are … they are simply fantastic! All hail insects!

About the author

Marlies Craig is an epidemiologist who used to research malaria, but now works for the Intergovernmental Panel on Climate Change. Though she did originally study Biology and Entomology, her love affair with insects is very personal. In her book What Insect Are You? – Entomology for Everyone, she shares that passion with young and old, see What Insect Are You? She hopes to kindle in people of all ages enthusiasm and a deeper appreciation of nature and show them why and how they can make a difference. She recently started a non-profit organisation called EASTER Action focussing on education and action in biodiversity, climate change, and sustainable living, see EASTERaction.org. At this time, EASTER Action is distributing a Covid-19 information booklet to help spread useful information and urge people to do what they can to overcome this crisis.