The Vanishing Insects

A Worldwide Challenge And How We Can Help At Home

Posted on: January 14th, 2021

Sheltering-in-Place Blog Entry #38

An adult male of Erythrodiplax laselva, a new species of dragonfly discovered in Costa Rica, dries out its wings while still clinging to the larval skin after emerging from the little pools of water of the bromeliad. Photo by C. L. de. la Rosa.

In April 1996, entomologist David Wagner collected a medium-sized dragonfly male adult at La Selva Biological Station. He was researching the distribution of several species of dragonflies and damselflies, a specialty of his. At that time, he didn’t recognize the species, so he sent it to another specialist, Dennis Paulson, who tentatively identified it as Erythrodiplax cf. amazonica (the “cf.” notation means “similar or approximating,” which meant that Paulson could not identify it with certainty either). Since Wagner did not collect other specimens during his trip, he placed the mystery dragonfly in a collection drawer and forgot all about it.

Sixteen years later, in 2012, while working as the director of the La Selva station and researching aquatic insects, I noticed a strange thing clinging to a leaf of a large bromeliad. Upon close inspection, I recognized the exuvia or cast skin of a dragonfly’s larvae, left behind by the adult when it emerged from the water. Think of the skins of cicadas that kids — and many adults — play with when they emerge in mass from their underground lives, ready to become adults and screech their way through the summer mating season. These cast skins are very useful in identifying species when the immature specimens have been described and associated with the adult stages.

E. laselva grabbing on to the larval skin as it pulls out its abdomen from the larval skin. Notice the wrinkled wings that will expand greatly in the next few hours. Photo by C. L. de. la Rosa.

I tried to key out the exuvia to species but couldn’t find anything close enough in the literature. But perhaps what piqued my curiosity the most was that I knew of several species of damselflies (cousins to the dragonflies, belonging to the same order, Odonata, but different suborder) that used the little pools of water that collect in the axils and center of bromeliads. This type of aquatic habitat is known as Phytotelmata, or plant-held waters. Phytotelmata support an incredible suite of aquatic insects, as well as vertebrates like poison frog larvae. I knew of no dragonflies that lived in these bromeliad pools, so the search was on to find a fully-grown nymph and see what emerged as an adult.

It didn’t take long. Early one morning, as I walked from my cabin in the rainforest to the station’s dining hall, I saw a fully-grown larva clinging to the underside of a bromeliad leaf, ready to perform that insect miracle of metamorphosis. A brand-new adult began to emerge from its immature stage in front of my wide-open eyes (and my camera). More specimens came later, giving my friend and colleague Bill Haber and David Wagner and me, all the information we needed to describe a new species for the world, Erythrodiplax laselva. Discovering and naming a new species is one of those things that weird people like me consider a thrill and a source of pride. We have a staggering number of species still to discover and name, to learn what they do and how they influence the world around them and our lives as well. But for many of these unknown species, time is running out.

Entomologists use strong black and white lights in front of a white sheet to attract night-flying insects. Photo by C. L. de. la Rosa.

This week Dave Wagner appeared in the international news, quoted in a National Geographic article talking about the disappearance of massive numbers of insects. The story explores the implications of insect decline and climate change summarized in a paper published in the Proceedings of the National Academy of Sciences, a very prestigious scientific publication (see ‘Further Reading’ below). The reports have been cited in many mass media outlets but what they talk about is not news for many of us that have worked with insects for many years. The steady, broad decline of insect populations and even the disappearance of many species that were abundant decades ago has been seen and experienced firsthand by many scientists and naturalists. While concerns have been raised for decades, the causes, consequences, and even awareness of these massive population declines have not sunk into our collective minds, and this is troublesome.

We have explored in previous essays the importance of insects and biodiversity in general to our wellbeing. Insects play many critical and essential roles in ecosystems, and we benefit from them in many ways. Without insects, many crops would fail, and many natural ecosystems would collapse. And as much as people often do not like to encounter many insects in their lives (butterflies are exempted, in general), we should be concerned about insect decline. And here is the good news, we can do something about it, too.

Modern techniques, such as DNA barcoding, help scientists identify and describe new species. Here, Dr. Bill Haber, an accomplished tropical entomologist, works with me to prepare samples for analysis at the La Selva Biological Station, Costa Rica. Photo by C. L. de. la Rosa.

Scientists are teaming up with conservationists and policymakers to create mechanisms for the protection of endangered species. Many initiatives address these issues. For example, creating and managing nature preserves, parks, and sanctuaries; advancing our knowledge through species inventories, descriptions, and DNA studies; and implementing policies to ban the use of dangerous agrochemicals that kill many non-target species, to name a few. But we can also contribute to these efforts in our backyards and communities.

Native plant gardens can be beautiful and very important for insect communities. Photo courtesy of the California Native Plant Society.

Besides helping scientists by participating in citizen science projects such as iNaturalist and local bioblitzes (see my last essay on citizen science here), we can create better conditions to support local insect populations by converting our pesticide and fertilizer-heavy lawns to more natural and gentle habitats for insects. The simple act of landscaping our yards with native plants and allowing insects to use them (yes, caterpillars will eat the leaves, but this is how they can become butterflies) contributes to their survival and the expansion of their populations. Simple actions, such as not raking all the leaves that blanket the soil in the fall, also support many insect species through the winter. Switching from pesticides and chemical fertilizers to more natural means of pest control and nutrient enrichment, such as home compost, can benefit essential species that we may not even know live in our yards. These species support backyard birds, shrews, and other creatures that share natural spaces with us, softening our cement, steel, and pavement footprint.

Monarch butterflies depend on milkweed  for nectar as well as food for their growing larvae. Planting milkweed in our gardens will help this beautiful threatened species. Photo by C. L. de. la Rosa.
A leafcutter bee collects pollen on its abdomen, nectar for energy, and leaf circles to make its nest. Here she is drinking from a native milkweed flower on Catalina Island. Photo by C. L. de. la Rosa.

There are many ways that we can become better stewards of our insect friends. Native gardens are an easy way to start, whether you create one in your yard, a community garden, or by joining natural restoration projects. The most important thing, though, is to decide to do something about it. While the small changes that we suggest here may seem like a drop in a bucket in the face of climate change and species extinction, you can still create an expanding wave of impact. One person can make a big difference in the world and it starts with you.

Yours in nature,

Carlos de la Rosa, Executive Director






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