How a parasitic fly makes termites harder to kill

When most people think about what makes a termite dangerous, they think about numbers. A colony of hundreds of thousands of individuals, working around the clock, invisible beneath your floors and inside your walls. They think about persistence — insects that cannot be reasoned with, negotiated with, or scared away. What they do not think about is a fly.

But in my research on Macrotermes gilvus, it is a fly that has taught me the most surprising lessons about just how resilient these insects can be. Not because the fly helps the termites. It kills them. But in the process of killing them, it does something genuinely remarkable: it makes them, for a period, significantly harder to destroy.

Understanding how that works requires stepping inside the termite colony, and into one of the stranger biological relationships I have encountered in my career.

The fly targets the major soldiers of termite colonies, the large-headed, powerful-mandibbled caste responsible for defending the colony against threats. Once M. mindeni deposits its eggs in association with them, a process begins that will gradually, systematically, and with extraordinary biological precision, hollow the soldier out from the inside.

The larva hatches and begins developing within the termite’s head capsule. In its second stage of development, it consumes the entire contents of the head before migrating into the abdomen for its third and final larval stage.

Eventually, when the larva is ready to pupate, it uses its breathing structures to apply lateral pressure against the termite’s abdominal wall, forcing body fluids outward and creating a dry microenvironment suitable for pupation. The host dies from the resulting trauma, or from the dehydration that follows.

It is, by any measure, not a gentle process. And yet the termite, throughout much of it, keeps functioning.

The fat reserves that keep a dying termite alive

When we analysed the body composition of parasitised soldiers, we found lipid levels of approximately 19.8% of total body mass. In healthy, unparasitised soldiers, that figure was around 6.1%. The infected termites were carrying more than three times the fat reserves of their healthy nestmates. This is not incidental.

Fat is energy storage, and the developing larva requires a continuous, substantial energy supply to complete its growth. The parasitoid has, in effect, engineered its host into a well-stocked larder.

The metabolic picture is more complex than simply storing more fat. Parasitised termites also show a significantly elevated metabolic rate. At the same time, they lose body water more slowly. Their cuticular permeability, the rate at which water passes through the outer surface of their bodies, is lower than in healthy termites. They actually contain less total water, but they hold onto what they have more effectively.

The result is an insect that, despite being slowly consumed from within, is physiologically equipped to survive conditions that would kill a healthy termite far sooner.

What the colony does

Here is where the story becomes even more interesting, because the parasitoid does not only manipulate its immediate host. It manipulates the host’s social environment too.

Termites are deeply social insects. Much of what makes them so successful as a species is their elaborate system of cooperative behaviour: workers feed soldiers through mouth-to-mouth contact, a process called trophallaxis, and groom one another in a behaviour known as allogrooming. These interactions are not random acts of care. They are precisely regulated, and they are central to how a colony maintains its health and distributes resources.

Redirecting the colony’s care system

When we observed parasitised soldiers within a living colony, we found that worker termites were paying them significantly more attention than their healthy nestmates. They were feeding them more frequently and grooming them more persistently. The feeding appeared to be actively solicited, with parasitised soldiers initiating trophallaxis through increased antennal contact, signalling their nutritional demands to the workers around them.

The parasitoid has found a way to redirect the colony’s social infrastructure toward its own benefit. The workers are not choosing to nurture the infected soldier out of any awareness of what is happening inside it. They are responding to signals, chemical and behavioural cues, that the parasitoid has, through the course of evolution, learned to exploit.

Grooming as defense mechanism

The presence of parasitised individuals in the colony also appeared to elevate the general level of grooming activity across the whole group, including among workers with no visible infection. Whether this represents a genuine defensive response, an attempt to detect and remove further parasitoids before they can establish, or something else entirely, is a question my research is still working to answer.

What this means for termite control

To be clear, Misotermes mindeni is not, in any practical sense, an ally in termite management. It is not present in sufficient numbers to meaningfully reduce a colony’s population, and its effects are targeted at individual soldiers rather than the colony as a whole.

What it reveals about termite biology has direct implications for how we approach controlling termite damage more broadly. Many conventional termite baiting strategies work, at least in part, by disrupting a colony's nutritional cycle. Bait is taken back to the colony, shared through trophallaxis, and gradually compromises the colony's ability to feed itself.

What the research shows us is that colonies are not uniform populations. Some individuals, for biological reasons entirely unrelated to our intervention, are significantly more resilient than others. A colony containing parasitised soldiers, carrying three times the normal fat reserves and capable of surviving starvation conditions nearly one and a half times longer than healthy termites, has a meaningful buffer against nutritional disruption.

Whether we are dealing with Coptotermes in Singapore or other subterranean species across the region, that biological complexity deserves our attention.

Why real-world monitoring matters

This is precisely why at Anticimex, we have invested in developing iTAS, our real-time termite alert system, built on continuous SMART monitoring rather than reactive detection. Understanding termite biology at this level of detail is what informs how we design our monitoring programmes, how we train our teams, and how we advise our clients.

A colony of termites is not a uniform population that will respond uniformly to treatment. It is a dynamic, biologically varied group of individuals, some of whom are, for reasons entirely unrelated to our intervention, significantly more resilient than others. Accounting for that complexity is not academic indulgence. It is what separates a monitoring strategy that works from one that simply appears to.

The deeper lesson

I began this research because I was curious about a fly. I continued it because what the fly revealed about termite biology kept surprising me, and because every surprise has turned out to have practical implications for the work of actually managing these insects in the real world.

Termites are not simple creatures. They are biologically sophisticated, socially complex, and embedded in ecological relationships that shape their behaviour and resilience in ways that are not always visible from the surface. Whether you are dealing with flying termites or subterranean colonies tunnelling beneath your foundations, the biology matters.

The parasitoid that is slowly killing one of the colony’s soldiers is simultaneously making that soldier harder to starve, ensuring it is better fed than its healthy nestmates, and raising the alert state of the entire colony around it. These are not separate phenomena. They are a single, interconnected biological system, and to manage termites effectively, we need to understand it as such.

That, in the end, is what decades of studying these insects has taught me. If you are concerned about termite activity in your building, the earlier you start monitoring, the better your position. You can learn more about Anticimex termite control solutions here.

The Insect That Rewrites the Rules: How a Parasitic Fly Makes Termites Harder to Kill