Flies and Wasps: The Creatures We Love to Hate — But Perhaps Cannot Afford to Lose
If I had to nominate one of the most irritating creatures in the natural world, the fly would probably be fairly high on my list.
There I am trying to work, perhaps writing, teaching or setting up an experiment, and a fly decides that the most interesting place in the entire room is somewhere within a few centimetres of my face.
Buzz.
It disappears.
Buzz.
It comes back.
Then it lands on the computer screen.
For other people, the equivalent creature is the wasp. A peaceful summer lunch in the garden can suddenly become an exercise in plate-covering, arm-waving and keeping a suspicious eye on something yellow and black that appears intensely interested in your drink.
It is very easy to conclude that both creatures are simply pests.
But biologically, that would be a serious mistake.
In fact, flies and wasps provide an excellent A-level Biology lesson because they demonstrate one of ecology's most important principles:
An organism does not need to be attractive, popular or convenient to be ecologically important.
Take away some of the creatures we regard as irritating and the effects could spread through an ecosystem in ways that are surprisingly profound.
Our View of Nature Is Often Very Selective
We tend to divide wildlife into rather human categories.
Butterflies are beautiful.
Bees are useful.
Ladybirds are welcome.
Dragonflies are impressive.
Flies are annoying.
Wasps are dangerous.
But ecosystems do not work according to our aesthetic preferences.
Evolution has not produced organisms because humans find them pleasant. Organisms occupy ecological niches because they have survived and reproduced successfully within complex networks of interactions.
That is a useful starting point for an A-level Biology student.
Rather than asking:
"Do I like this organism?"
biology asks:
"What does this organism do?"
And once we ask that question about flies and wasps, they become considerably more interesting.
First: What Exactly Is a Fly?
When most people say "fly", they are probably imagining the familiar housefly.
But biologically, flies are an enormous group of insects belonging to the order Diptera.
The name is useful.
"Di" means two and "ptera" relates to wings.
Unlike most flying insects, true flies have only one functional pair of wings. Their second pair has evolved into small balancing structures called halteres, which help them control their flight.
That partly explains one of the things that makes flies so irritating.
They are exceptionally manoeuvrable.
Trying to swat one is effectively trying to outmanoeuvre an animal equipped with a sophisticated biological flight-control system refined by millions of years of natural selection.
Suddenly missing it with the newspaper feels slightly less embarrassing.
The Diptera include:
- houseflies;
- hoverflies;
- blowflies;
- crane flies;
- mosquitoes;
- midges;
- fruit flies;
- horseflies;
- numerous other groups.
So saying "flies are useless" is rather like saying "mammals are useless" because you dislike rats.
The group is enormously diverse.
Flies as Pollinators
When we think of pollination, bees receive most of the publicity.
Quite rightly, bees are extremely important pollinators.
But they are not alone.
Many flies visit flowers to feed on nectar and pollen, and as they move from flower to flower they can transfer pollen between plants.
Hoverflies are particularly noticeable examples.
Some are remarkably bee-like in appearance, an example that can lead into another excellent biological topic: mimicry.
A harmless hoverfly with yellow and black markings may receive some protection from predators because it resembles a stinging insect.
But hoverflies are more than convincing impersonators.
They can also be useful pollinators.
That gives us an immediate ecological interaction:
Plant produces nectar -> fly visits plant -> pollen is transferred -> plant reproduction is increased.
The fly receives food.
The plant receives a reproductive advantage.
That is a form of mutualistic interaction.
Pollination Is Really About Plant Sex
This is where an apparently simple discussion about irritating insects suddenly becomes very relevant to A-level Biology.
For sexual reproduction in flowering plants, pollen must ultimately reach the appropriate female reproductive structures.
Animals visiting flowers can act as biological transport systems.
Pollen attaches to their bodies.
When they visit another flower, some may be deposited.
That can result in fertilisation, seed production and eventually the next generation of plants.
Remove enough pollinating insects and reproduction may decline.
And if those plants form part of a food web, the consequences do not necessarily stop with the plant.
Flies Are Also Nature's Recycling Department
Perhaps the most important ecological role of many flies is less attractive.
They eat dead things.
Or, more accurately in many cases, their larvae do.
That may not make for an appealing poster campaign, but decomposition is absolutely fundamental to ecosystems.
Imagine a woodland in which organisms died but nothing decomposed them.
Dead leaves would accumulate.
Dead animals would remain.
Faecal material would build up.
Most importantly, valuable nutrients would remain locked inside this organic matter.
Decomposers and detritivores help return those nutrients to ecological cycles.
The Maggot Has a Job
The word "maggot" is not particularly good public relations.
But maggots are simply the larval stage of certain flies.
For some species, adult flies locate decomposing organic material and lay eggs upon it.
The larvae hatch into an environment rich in food.
They feed rapidly.
Their activity contributes to the breakdown of the material.
Other decomposers, including bacteria and fungi, are also involved.
Eventually nutrients that were locked inside tissues can become available again.
A simplified sequence might be:
Dead organism -> decomposers and detritivores -> mineral ions -> plant uptake -> new biomass
That is nutrient cycling in action.
Without decomposition, ecosystems could not continue functioning indefinitely.
A Dead Animal Is Actually an Ecosystem
This is something I think students sometimes overlook.
Finding a dead animal may simply look unpleasant.
Biologically, however, it is a dramatic transfer of energy and nutrients.
Almost immediately, organisms begin exploiting that resource.
Different insects may arrive at different stages of decomposition.
Microorganisms multiply.
Predators arrive to eat the insects.
Nutrients eventually enter the soil.
Plants may absorb them.
Those plants are eaten by herbivores.
The atoms that once formed one organism can eventually become part of completely different organisms.
This is one of the wonderful ideas in biology.
Matter is continually recycled.
The carbon atom in your body today may once have been part of a tree, a bacterium, another animal or the atmosphere.
Flies are part of that recycling machinery.
Flies Can Even Help Solve Crimes
The predictable colonisation of dead organisms by insects has given rise to forensic entomology.
Certain fly species tend to arrive at carcasses during particular stages of decomposition.
Their eggs and larvae develop at rates influenced by factors such as temperature.
By identifying insect species and estimating their developmental stage, forensic scientists can sometimes obtain information relevant to estimating the period since death.
For an A-level Biology student, this creates links between several topics:
- life cycles;
- development;
- enzymes;
- temperature;
- ecosystems;
- succession;
- classification.
Something as seemingly unpleasant as a blowfly larva therefore connects ecology with forensic science.
Then There Are Wasps
Wasps have an even worse public-relations problem.
A bee approaching a flower is usually tolerated.
A wasp approaching a glass of lemonade frequently causes an entirely different reaction.
But once again, "wasp" describes a vast range of organisms.
Only a relatively small proportion are the familiar social wasps that build colonies and interact frequently with people.
There are many thousands of species with extraordinarily diverse lifestyles.
And ecologically they can be extremely important.
Wasps Are Predators
One of the most important things wasps do is eat other animals.
Or feed other animals to their larvae.
Many wasps hunt insects and other invertebrates.
That means they can contribute to regulating populations.
Consider a simple food chain:
Plant -> caterpillar -> wasp
The caterpillar consumes plant tissue.
The wasp consumes the caterpillar.
If predators disappear, prey populations can sometimes increase significantly.
That can produce a trophic cascade, where changes at one level of a food web influence other trophic levels.
So the wasp hovering around the garden may also belong to a group of organisms helping to regulate herbivorous insect populations.
Wasps as Natural Pest Control
Imagine a crop containing large numbers of insect herbivores.
If those insects reproduce rapidly, crop damage may increase.
One solution is pesticide.
But another form of control already exists in nature:
predators and parasitoids.
Wasps are particularly important here.
Some species hunt prey directly.
Others have an even more remarkable reproductive strategy.
The Extraordinary World of Parasitoid Wasps
Parasitoid wasps provide one of biology's more dramatic life histories.
A female may lay an egg inside or on another arthropod.
The wasp larva then develops using the host as a source of nutrients.
Eventually the host dies.
This differs from ordinary parasitism.
A parasite normally benefits from keeping its host alive for some time.
A parasitoid ultimately kills its host.
It sounds like something invented for a science-fiction film.
It is actually happening in gardens, fields and ecosystems around us.
Parasitoids and Biological Control
Parasitoid wasps can have considerable importance in agriculture because many attack insects regarded as crop pests.
Instead of relying entirely on chemical pesticides, growers can sometimes exploit natural enemies.
That leads directly into A-level discussions of biological control.
Suppose a crop pest increases rapidly.
A parasitoid species that attacks that pest may reduce its population.
Potential advantages include reduced pesticide use and greater specificity.
But biological control must also be approached carefully.
Introducing organisms into ecosystems can have unexpected consequences if their interactions with native species are poorly understood.
Once again, a small wasp opens the door to a much bigger ecological discussion.
Wasps Pollinate Too
Although predation is perhaps their most interesting ecological role, many adult wasps also visit flowers.
They require carbohydrates for energy and may feed on nectar.
As they travel between flowers they can carry pollen.
So wasps may function simultaneously as:
- predators;
- pollinators;
- prey;
- competitors;
- hosts or parasites themselves.
This illustrates something fundamental about ecosystems.
Organisms rarely have only one relationship.
A Food Chain Is Too Simple
GCSE Biology often introduces ecology through food chains.
Grass -> caterpillar -> bird
They are useful models.
But real ecosystems do not contain isolated food chains.
They contain food webs.
Add flies and wasps and the network quickly becomes complicated.
Imagine:
Flowering plant -> hoverfly
Plant -> caterpillar -> wasp
Dead caterpillar -> fly larvae
Fly -> spider
Fly -> bird
Wasp -> bird
Nutrients from decomposition -> plant
Already the neat linear chain has become a network.
And even that is an extreme simplification.
Ecosystems Are Networks, Not Lists
This is one reason biodiversity matters.
Imagine removing one species from an ecosystem.
Another species may consume the same food, so perhaps very little initially changes.
Ecologists sometimes refer to this as functional redundancy.
But remove enough species performing similar ecological roles and the resilience of the system may decline.
It is rather like removing components from a complicated machine.
One missing component may not stop it.
Several missing components might.
The problem is that we often do not know exactly where that threshold lies.
"What Would Happen If All the Flies Disappeared?"
This makes an excellent classroom question.
At first, students may answer:
"Brilliant."
Then start exploring the consequences.
There could be less pollination by fly species.
Decomposition pathways could change.
Animals that eat flies would lose part of their food supply.
Competition between decomposers might change.
Nutrient cycling could be affected.
Plants dependent upon particular pollinators could decline.
Predators dependent upon those insects might then decline.
We should be careful not to claim that ecosystems would instantly collapse because every ecological system is different and other organisms can perform overlapping roles.
But it is equally wrong to imagine that removing an enormous and diverse group of organisms would have no consequences.
And What If the Wasps Disappeared?
Initially, picnics might become considerably more relaxing.
But ecological consequences could include reduced predation on other insects.
Some prey populations could increase.
Plant damage from herbivorous insects might therefore increase.
Certain pollination relationships could disappear.
Animals that eat wasps would lose a food source.
Parasitoid-host relationships would vanish.
Food-web structure would change.
The very creature we regard as a pest may itself be controlling organisms that would otherwise become pests.
The Ecological Importance of Being Eaten
This may sound a little harsh, but another important function of both flies and wasps is simply that other organisms eat them.
Birds eat flies.
Spiders eat flies.
Amphibians eat flies.
Fish eat aquatic fly larvae.
Dragonflies eat flying insects.
Other insects eat insects.
Wasps themselves are eaten by various predators.
An organism does not need to perform some sophisticated ecosystem service to matter.
Sometimes being food is enough.
Energy captured originally by photosynthetic organisms moves through ecosystems via feeding relationships.
Ultimately:
Sunlight -> producer -> consumer -> consumer
The insect buzzing around the window represents stored chemical energy.
To another organism, it is lunch.
The Energy Eventually Came From the Sun
We can take this idea further for A-level Biology.
Plants capture light energy during photosynthesis.
Some of that energy becomes chemical energy stored in organic molecules.
Herbivores consume plants.
Predators consume herbivores.
Detritivores consume dead material.
At each trophic transfer, some energy is lost from the biological system, largely through respiration and heat.
So a wasp catching a caterpillar represents energy moving through trophic levels.
A fly larva feeding upon decomposing material represents another route through the ecosystem.
Ecology becomes much more interesting when we stop thinking of organisms independently and start following energy and matter through the system.
A Useful Practical Investigation: Who Visits the Flowers?
This can make a surprisingly good ecological investigation.
Choose several flowering plant species and observe them for fixed periods.
For example:
10 minutes per plant.
Record visitors as categories such as:
- bees;
- hoverflies;
- other flies;
- wasps;
- butterflies;
- beetles;
- other insects.
Repeat observations at different times of day.
You could investigate whether flower colour, shape or location affects visitor frequency.
Students could calculate:
Number of visits per minute = Total visits / Observation time
They could then compare different flowers.
Immediately you have:
- sampling;
- quantitative data;
- behavioural ecology;
- pollination;
- biodiversity;
- experimental controls;
- reliability.
And students may discover that flowers are being visited by far more than bees.
Another Investigation: Decomposition
A second area worth exploring is decomposition.
This needs sensible hygiene precautions, and I would avoid experimenting with rotting animal material.
Plant material provides a much safer alternative.
Students could compare decomposition of leaves under different conditions.
Variables might include:
- temperature;
- moisture;
- oxygen availability;
- surface area.
One prediction might be:
Increasing temperature increases decomposition rate up to an optimum because decomposer enzymes operate more rapidly.
But at sufficiently high temperatures, enzymes can denature and organisms may die.
That links ecology beautifully with enzyme kinetics.
Temperature Matters to Insects Too
Flies and wasps are ectothermic.
Their body temperature and metabolic activity are strongly influenced by environmental temperature.
That helps explain why insects often become much more obvious during warm weather.
It also raises interesting questions about climate change.
If average temperatures change, then:
- geographical distributions may change;
- breeding seasons may change;
- emergence dates may shift;
- interactions between predators and prey may change;
- interactions between pollinators and flowering plants may become mismatched.
Ecology is full of timing.
If two interacting species respond differently to environmental change, their relationship may be disrupted.
Population Control Is Never Quite as Simple as It Looks
Consider a hypothetical insect pest.
Its population increases.
Predatory wasps now have more food.
Their population may subsequently increase.
That could reduce the prey population.
As prey becomes scarce, wasp numbers may then decline.
This creates the possibility of population cycles.
A simplified model might be:
More prey -> more predators -> fewer prey -> fewer predators -> prey recovers
Real ecosystems are vastly more complicated, but this provides an introduction to predator-prey dynamics.
Students encountering population curves should remember that behind every line on the graph are real organisms interacting with one another.
Natural Selection Has Produced Some Extraordinary Adaptations
Both flies and wasps provide superb examples of adaptation.
Flies may possess:
- compound eyes;
- rapid visual processing;
- highly manoeuvrable flight;
- specialised mouthparts;
- remarkable reproductive rates.
Wasps may possess:
- venom;
- ovipositors;
- powerful sensory systems;
- specialised hunting behaviour;
- complex social organisation;
- precise host recognition in parasitoid species.
Each characteristic exists within an evolutionary context.
Variation occurs.
Selection acts.
Individuals possessing advantageous characteristics may leave more offspring.
Allele frequencies can therefore change between generations.
The irritating insect buzzing around the room is also the product of an enormous evolutionary history.
Why Does a Fly Seem So Good at Avoiding Me?
There is a nice biological question hidden here too.
A fly does not experience its environment exactly as we do.
Its visual system is particularly effective at detecting movement.
When a large object moves towards it, sensory information triggers rapid escape behaviour.
Natural selection strongly favours this ability.
A fly that responds slowly to approaching predators is unlikely to enjoy a particularly successful reproductive career.
Generation after generation, successful escape responses are selected.
So each time I unsuccessfully attempt to persuade a fly to leave my workspace, I am essentially encountering the consequences of natural selection.
Why Do Wasps Become So Noticeable in Late Summer?
The familiar social wasps we encounter around food have seasonal colony cycles.
Earlier in the season, workers are heavily involved in obtaining resources for the developing colony.
Later, colony organisation changes and workers may become much more noticeable around sugary foods.
From our point of view, it can seem as though wasps have suddenly decided to ruin August.
From their perspective, they are simply responding to biological needs and available resources.
Behaviour that seems irrational or aggressive to us may make considerably more sense once examined through ecology and evolution.
This Raises an Interesting Question About "Pests"
What exactly is a pest?
Biologically, there is no taxonomic category called "pest".
It is largely a human label.
An organism becomes a pest when its activities conflict with ours.
A fly decomposing animal waste somewhere in the countryside may be performing an ecological service.
The same species walking across our food becomes a hygiene concern.
A wasp hunting caterpillars among plants may be welcome.
The same wasp entering a bedroom may not be.
Context changes our judgement.
The organism has not changed.
That Does Not Mean We Should Ignore the Risks
Ecological importance does not mean every interaction with an organism is desirable.
Some flies can transmit pathogens.
Some fly species bite.
Mosquitoes, themselves members of Diptera, are vectors for major human diseases.
Wasps can sting, and for someone with a severe allergy that can become medically serious.
Understanding an organism's ecological importance does not require pretending that it can never cause problems.
Biology is more interesting than that.
An organism can be simultaneously:
ecologically valuable and inconvenient to humans.
A-Level Biology Is Full of These Apparent Contradictions
Predators kill other animals but may stabilise ecosystems.
Parasites harm hosts but influence population dynamics.
Bacteria cause disease but also drive nutrient cycles.
Fungi spoil food but make decomposition possible.
Wasps sting us but kill crop pests.
Flies contaminate food but recycle nutrients and pollinate plants.
Nature rarely divides itself neatly into "good" and "bad".
Those are human categories.
Ecology is about relationships and consequences.
A Challenge for Students: Build the Fly-and-Wasp Food Web
Start with these organisms:
- flowering plant;
- caterpillar;
- aphid;
- hoverfly;
- predatory wasp;
- parasitoid wasp;
- spider;
- bird;
- dead organic material;
- bacteria;
- fungi.
Now connect them.
Who eats whom?
Who pollinates whom?
What decomposes what?
What competes with what?
Which organisms could occupy several roles?
Then remove one organism.
What happens?
Remove another.
What happens now?
This is much closer to real ecological thinking than memorising a single food chain.
It Also Changes the Way We Think About Conservation
Conservation naturally attracts attention towards charismatic organisms.
Tigers.
Elephants.
Whales.
Pandas.
They are important and compelling.
But ecosystems also depend on an immense number of much smaller organisms that rarely appear on conservation posters.
Insects are part of the biological infrastructure of the planet.
Pollination, decomposition, predation and food-web interactions often depend on them.
Saving biodiversity therefore cannot simply mean protecting the species we happen to like.
Perhaps We Need to Protect the Irritating Ones Too
This is probably the part I find most interesting.
I do not particularly want a fly circling my head while I am trying to work.
Nor do I especially want a wasp crawling into my drink.
But I can simultaneously recognise that both belong to functioning ecosystems.
Perhaps that is one of the marks of understanding biology.
We stop asking whether nature is convenient for us and start asking how it works.
And sometimes the answer is:
It works partly because of the organisms we wish would go away.
A Different Way of Looking at the Next Fly
So the next time that familiar buzzing starts beside my computer, I doubt I shall suddenly welcome the visitor enthusiastically.
I will probably still encourage it towards the open window.
But perhaps with slightly more respect.
Because somewhere beyond my annoyance is an animal belonging to one of the most successful groups of organisms on Earth.
Its relatives pollinate flowers.
Others recycle dead material.
Others feed birds, spiders, amphibians and fish.
Others have transformed our understanding of genetics.
Wasps deserve a similar reassessment.
They are predators, parasitoids, pollinators and prey, forming part of complex ecological networks that regulate populations and transfer energy through ecosystems.
They may be irritating.
They may occasionally be dangerous.
But useless?
Definitely not.
Conclusion: Ecology Does Not Care Whether We Like Something
Perhaps one of the most important lessons we can teach through A-level Biology is that ecosystems are not collections of species living independently.
They are networks.
Remove one connection and perhaps very little happens.
Remove hundreds or thousands and eventually the network becomes weaker.
That is why biodiversity matters.
Not simply because having lots of different species is interesting, but because those organisms perform countless interacting ecological roles.
So perhaps we should reserve the word "useless" rather carefully.
The fly buzzing around my desk may still irritate me.
The wasp arriving at the picnic may still encourage everyone to move their drinks.
But both remind us of an important biological truth:
Nature is full of organisms whose importance becomes obvious only when we stop looking at them from a purely human point of view.
And the creature we would most happily remove from the ecosystem might turn out to be one of the creatures quietly helping to keep it functioning.
