The insect boom: How Botswana’s green season explodes with life

‘One of the things that truly defines summer in northern Botswana,’ says Mpho, a Wilderness Environmental Impact Officer based in the region, ‘is not just the heat, nor the sudden flush of green that spreads across the landscape after the first rains. It is the explosion of insect life.

‘The most recognisable of these blooms is the emergence of flying termite swarmers (termites out to mate) in the hundreds of thousands, filling the air during the day and swarming around every light source at night. This seasonal irruption marks the beginning of an important breeding period for many insect species, in anticipation of abundant food during the rainy summer months. In the case of termites, these alates are actually the reproductive phase of the colony’s life cycle. 

‘What makes this phenomenon even more fascinating,’ Mpho adds, ‘is how interconnected it is with the wider ecosystem. The insect bloom itself is driven by the rapid growth of grasses, flowers, and other vegetation just before and after the first rains, but it also becomes an open invitation to countless other animals that feed on insects.’ 

Like birds. Botswana is at its best for birdwatching during green season. Mpho is an avian enthusiast, humbly calling himself a birder rather than an expert, though he knows a thing or two about birds, particularly vultures. 

‘Long-distance bird migration is driven by this!’ he says of the insect explosion. ‘Every year birds from as far north as Europe and Asia, as well as other parts of Africa, undertake extraordinary journeys to arrive in Botswana just in time for summer. Species such as the European roller, European bee-eater, and various storks suddenly become common sights across the Delta and Linyanti, spending the season here before departing at the end of summer, and repeating this every year. 

‘It is all part of a magnificent chain reaction within the food web, where the rains trigger plant growth, plant growth fuels insect blooms, and insects in turn sustain the exceptional diversity of wildlife here.’ 

‘Following the first significant rains, dormant eggs hatch, soil moisture rises, vegetation flushes green, and temporary wetlands and floodplains fill with water,’ explains Mariëtte, Wilderness Group Biodiversity Co-ordinator.  ‘Warm temperatures combined with moisture create ideal breeding conditions for enormous numbers of insects.

‘It is not a single event,’ Mariëtte adds, ‘but rather a cascading emergence of multiple insect groups – termites, flying ants, beetles, moths, mosquitoes, grasshoppers, dragonflies, midges, aquatic insects, and caterpillars, among others. Many species spend the dry season underground, in egg form, or in diapause (a form of dormancy), waiting for the environmental cues of rain, humidity, and temperature.

‘Ecologically, insects form the foundation of the seasonal food web,’ she continues. ‘The immediate effect is an enormous increase in available protein and energy across the ecosystem. Birds breed to coincide with peak insect abundance, amphibians emerge and reproduce explosively themselves, reptiles become more active, and many mammals benefit indirectly through improved grazing and browsing conditions driven by nutrient cycling.’

Mariëtte lists some of the critical ecological functions performed by insects: the pollination of flowering plants; nutrient recycling through decomposition; soil aeration and enrichment; seed dispersal; waste removal; and support for aquatic food chains.  

‘Different insect groups peak at different times,’ Mariëtte says. ‘Termite emergences often follow the first heavy storms. Mosquitoes and aquatic insects build as water accumulates. Caterpillars and grasshoppers increase as vegetation develops, and dragonflies often peak later as wetlands stabilise.’

The sequence continues until March or April, when insect numbers decline, temperatures cool slightly, rainfall diminishes, ephemeral pools dry up, and vegetation begins transitioning toward the dry season.

‘Insect abundance supports a huge range of wildlife,’ Mariëtte explains. ‘Birds are perhaps the most obvious beneficiaries. Bee-eaters feed heavily on flying insects; swallows, martins and numerous raprots hunt aerial insects continuously; drongos catch insects flushed by mammals; rollers, hoopoes, hornbills, and starlings consume beetles, grasshoppers, and caterpillars; herons and storks feed on aquatic insects and larvae. 

‘Reptiles and amphibians also respond dramatically,’ she adds. ‘Frogs breed instantaneously to exploit insect abundance; lizards and geckos feed on emerging insects; and bats consume enormous numbers of mosquitoes and moths nightly.’

Many small mammals and primates add insects to their diet during green season, especially termites and caterpillars. Large mammals generally don’t feed on insects for nutrition, but may do so – or otherwise benefit from the plethora of insects – at that time of year.

‘Elephants sometimes deliberately consume termite mound soil for the minerals. It’s known as geophagy,’ Mariëtte says. ‘Warthogs and baboons may dig for termites; honey badgers actively raid termite and bee colonies; buffalo, giraffe, zebra, and antelope indirectly benefit because insect-driven nutrient cycling improves plant productivity. Large predators do not meaningfully feed on insects, although lions and hyenas may incidentally ingest them.’

Certain species’ birthing schedules coincide with the insect explosion. As Mariëtte reveals: ‘Most antelope species in northern Botswana time births to coincide with the broader productivity pulse created by the rains. While they are not responding specifically to insects themselves, the insect explosion is part of the same ecological cascade. 

‘Species such as impala, lechwe, tsessebe, and wildebeest often synchronise births so that lactating females and growing young have access to optimal forage conditions. Many bird species time breeding much more directly around insect abundance, because nestlings require extremely protein-rich diets.’

The green season insect boom has long had significance for humans, too. Mopane worms and flying termites proliferate, providing highly nutritious food sources and local income. Insects also influence seasonal fishing success; crop dynamics; pollination; tourism and birdwatching opportunities; traditional ecological knowledge; cultural memory; and seasonal patterns in rural communities. 

‘Long before modern weather forecasting existed, people read the signs of the natural world to understand the changing seasons,’ Mpho says. ‘The sudden appearance of flying termites, for example, has traditionally been understood as a sign that rains are imminent. In farming and pastoral communities, these insect emergences often signal the true arrival of summer and the beginning of a hopeful season ahead. 

‘The arrival of migratory birds carries similar meaning. One of the most recognised is the Abdim’s stork, traditionally known in some communities as the “Rain Bird”. Its appearance is often treated as near-certain confirmation that the rainy season has begun.’

In spite of its downside – an increase in mosquitos means an elevated malaria risk; problematic tsetse flies in some areas; crop pests possibly increasing in wetter years; and insect swarms sometimes affecting visibility and daily activities – the insect irruption weighs in on the positive side of the scale. 

As Mariëtte says, ‘it’s less of an ecological nuisance and more like a vital, annual life rhythm.’