Netwinged insects: The invisible caretakers of forests

Insects are known more for the harm they cause than for the good they do. But diverse families of insects are doing the job of protecting forests from sap sucking, root chewing, flower gorging and fruit mauling creatures. Lesser known among such insects are the netwinged insects and their close cousins the snakeflies, dobsonflies and fishflies.

The netwinged insects of order Neuroptera are predators that feed on other insects and thereby keep a check on sap sucking insects that could cause much harm to trees and other plants in a forest. The larvae of all species and several adults are predators, benefitting forest ecology immensely. Unfortunately, many of these species in India remain undiscovered and their potential as caretakers of forests is unexplored.

Based on data from global satellites, a recent report claimed that in the year 2017, a forest the size of a football pitch was lost every second. Global Forest Watch says the loss was 29.4 million hectares. Left undisturbed, this trend can be reversed. Forests can expand and regenerate in ways we are yet to understand holistically. But a host of forest vegetarians − from microscopic bacteria and fungi to large mammals and birds − can make this expansion difficult. These organisms defoliate (remove leaves), chew through roots, infect or eat away flowers and fruits, sometimes to an extent that the tree dies off. The trees and plants in turn, have evolved ways to protect themselves from such onslaughts including help from a host of friendly creatures like the the netwinged insects.

Meet the Neuropteridans

At first glance you would take them for a dragonfly and a damselfly. A closer look will reveal the masqueraders are actually the owlfly and antlion, making you marvel the extent of mimicry in the insect world.

Another family member is the lacewing, aptly known as the “aphid lion” since its larva hunts to consume up to 200 aphids in a week. In the absence of aphids (small sap sucking bugs), a combination of insect eggs, mites, thrips, caterpillars and white flies will do to keep its hunger at bay.

And then there’s the mantisipid. Not only does it live among spiders to gorge on their eggs, but the mantispid’s larvae also piggy back on the spiders to move from web to web in search of their next wholesome meal. The spider however is hardly aware of their presence.

These larvae (juvenile form of organisms), whose ecological function in the forest is highly valuable, are so well camouflaged in their environment that they remain practically invisible to the human eye.

Welcome to the world of net-winged insects, the Neuropteridans.

These soft-bodied insects are petite and elegant. Whether it is the mantidfly, antlion, owlfly, lacewing, dustywings, snakefly or dobsonfly, their colourful and transparent wings, like well-woven lace, are their identity. Neuropterans are found in forests, woodlands, shrub habitats and in grass dominated vegetation. Their diversity is abundant in the tropics yet, their ecology is poorly understood.

The larvae are specialised for predation, possessing elongated and sometimes curved mandibles (appendages near the insect mouth) that can pierce and suck the fluids off the body of their predators. When predator-prey relationships are discussed these small insects are rarely chosen as examples. However, no lion feeding on a deer can match the ecosystem services an aphid-lion or other Neuropteran larvae provide a forest.

The feeding cycle of the larvae is of significance since the larvae take two to three years to turn into an adult. Through all this time of feeding, the larvae do not excrete. Their bodies undergo changes just before pupation, the stage where the insects transition from juvenile to mature, so that the accumulated waste can be released. Some Neuropterans innovatively use a part of this stored excreta to produce silk to cocoon their pupa.

The netwinged insects’ diverse range of habitats and life strategies help in the functioning of natural ecosystems. Those who study them believe that the Neuroptera are excellent indicators of environmental and habitat transformation.

Colourful little saviours of the forest 

Perhaps the more popular among netwinged insects, are the antlions. So far nearly 126 species have been reported from India. Folklore abound in cultures across the world. Children love playing with them. When astronaut Charles Duke from the Apollo 16 mission saw the craters on the moon, he compared them to the antlion pits. History is replete with whimsical stories about them; the “gold-digging ants” from India is one of the most unlikely account of their abilities.

Popularly known as the doodle bug in the West, the name antlion describes the larva of the Neuropteran from the family Myrmeleontidae. The adults resemble a damselfly but their long antennae with a small club at the tip and their large wings kept folded covering their body help identify them. Their prey are predominantly the ants but other small insects too are occasionally hunted.

Closely related to antlions, yet quite distinctly different in ecology and behaviour, are the owlflies, another important caretaker of the forest. Visually, they are a treat to watch. The adults look, behave and share aerial space with the dragonfly for whom they are also the prey. To avoid competition for prey as well as being eaten by them, these insects hunt during dawn and dusk and rest among twigs and grasses during daytime. While on a twig their wings are held down sideways and the long abdomen is kept lifted up, protruding from the body to resemble a tree twig. This fools most insects, except the dragonflies. The long antennae with a prominent knob at the tip is the easiest way to recognise them. Like the adult, the larvae too are excellent at disguise and difficult to spot. They are voracious feeders of a variety of sap sucking insects and others. The eggs are laid in a row on the tip of leaf blades and the young larvae break open the lid to come out newly emerged larvae and their egg case.  As both adults and larvae hunt insects they are valuable for the health of a forest. Yet worldwide these are among the most poorly studied creatures.

Many Neuropterans go by the name of lacewings but are from different families, with differing forms and ecological behaviours. These range in size from the four millimetres long but tiny, brown lacewing to the giant or moth lacewing with a wingspan of 60 mm. Green in colour with prominent copper-coloured eyes, the Chrysoperla or the green lacewings are quite familiar among gardeners. The less common are the pink, purple and yellow coloured species. They are not easily spotted as most of them are nightfliers. The adults will come to light but their larvae will be harder to spot. They camouflage themselves with the debris found in soils that would sometimes contain even the dead prey. Lacewings lay their eggs on silken stalks that are the first proteinaceous food for the emerging larva. Some species are even cannibalistic, fighting their own larvae-brethrens and taking them as food. Lacewing larvae protect trees like the cedar, walnut and birches from aphids, leaf-miners, leafhoppers and whiteflies; some feed on the citrus blackflies protecting the economically useful citrus trees.

The mantidfly is often mistaken to be the praying mantis. Its first pair of legs resemble the ones seen in mantis – raptorial, armed with spines and held folded. Not so obvious is the distinct difference in the way both these insects hold their folded legs. Some species additionally sport the colour and markings of a commonly flying paperwasp resulting in confusions galore. But the wings and the colourful prominent eye tell you that you are looking at a mantidfly and not a mantis or a wasp. An extended neck and an arched abdomen give them an almost comical but distinct appearance. Mantidflies are quite fast and adept at catching and feeding on live prey – a variety of flying insects, some that injure plant parts. They are most abundant in the tropics where the adults are active after dusk. Unlike the lacewings, but like the owlfly adults, these are hunters that fly well to search for their insect-prey. Their larvae though are a different story altogether.

Mantidfly larvae are spider-egg feeders. Like the lacewings, the eggs of mantidflies are also stalked. The larvae hatching out of the eggs wait on the stalks to board a spider. The spiders then take them to their webs where they wait for the eggs to be laid. The mantidflies penetrate the eggs and feed on its contents. There is quite a scuffle among the larvae but the spider is blissfully unaware of the drama in its web.

There are several big and small carnivorous species of Neuropterans and their close relatives that live in the wild. The dusty wings looking more like a tiny wasp are small and feed on mites. They live in the mountainous regions of northern India, where both adults and larvae are expert hunters of insects and allied harmful invertebrates. Spoon-winged lacewings, named due to the dilated hindwings are quite striking to look at. While the adults are pollen feeders, the larvae are generalist predators, gleefully accepting any prey that comes their way.

Will these forest protecting insects be able to survive amidst the disappearing wilderness? Tough to know as the Neuropterans are of interest to very few. Conservation of tiger and elephant habitats may provide some succour to these small organisms, but the disappearing small and middle habitats are a cause of worry since the larvae of netwinged insects need specific conditions and long periods to develop into adults.

CITATION:

Entomology Ecology & Biodiversity – Tyagi, B.K., Veer, V; Scientific Publishers, India

The Weavers-The Curious World of Insects – Geetha Iyer. Pgs 111-133; Harper Collins Publishers India