10 Weird Facts About the Hornet Robberfly

The United Kingdom. This is where you need if you want to see the famous Hornet Robberfly and you might want to do it soon. This is an endangered species of almost-hornet-but-not-quite flies that also rank as the largest in the UK. The Hornet Robberfly can grow up to 1 inch in ideal living conditions, which is already impressive by fly expectations.

But there’s more to this insect than its confusing name and impressive size. Since you can find it in Europe, this insect hardly qualifies as an exotic animal. Yet, there are few insects, and even creatures in general, that are as fascinating as this one.

Today, we will discuss 10 of the most compelling facts about the Hornet Robberfly. What makes it unique, and why should it impress you?

1. Eye-catchy Appearance

The Hornet Robberfly is only a hornet by name. In reality, it’s just a fly, although ‘just’ may not be the appropriate word here. The reality is that this insect qualifies as a biological fly, looks like a hornet, and feeds like a spider. Its appearance is equally as confusing, as the fly displays a long and yellow-ish body with thick, powerful, and spiky legs.

The fly possesses one set of wings and has a thick thorax with yellow hairs. Its large, black eyes flank a short but powerful proboscis designed to kill and suck the juices and life out of other insects.

We don’t know much about why the fly resembles a hornet, but the most likely reason is protection. Predators may confuse the fly for a hornet and avoid it instinctively. This means that the fly’s coloring and body pattern functions as a camouflage mechanism.

Such an adaptation is nothing new in flies. These are highly adaptable creatures with rather astounding defensive mechanisms, the most prevalent one being Batesian mimicry. To put it shortly, this mechanism refers to flies mimicking the appearance of bees, ants, and wasps to avoid predators. The Hornet Robberfly and Large Bee-Fly are great examples in this sense.

Some species are myrmecophilous, which means that their larvae are grown by ants. This is possible due to the formers’ ability to produce ant-specific pheromones, making ants believe they are of the same species.

2. Unusual Diet

To begin this point with an obvious fact, all flies have unusual diets. The fly’s eating pattern changes according to its stage of development. Depending on the species, the larvae may be herbivores, decomposers, parasites, or scavengers, primarily feeding on dead organic matter. You may know these larvae by their popular name of maggots.

The Hornet Robberfly is a carnivorous hunter at its tiny little heart. It will attack a variety of insects, including fellow Robberflies and other fly species. The fly will use its hard and lethal proboscis to latch onto unsuspecting insects and suck them dry.

The feeding process is similar to any other fly species in the sense that the Hornet Robberfly will liquefy the prey’s insides, then drink the resulting fluids. Few things are as fascinating and as gross as the fly’s feeding mechanism. At least the fly will kill its prey prior to feeding, unlike other predatorial and parasitic insects like the Tarantula Hawk wasp.

3. Possesses a Powerful Venom

The Hornet Robberfly possesses a potent venom that’s generally harmless to humans. It will only inflict some pain and irritation at the site of the bite, but nothing more. Theoretically, the fly’s bite may cause more serious allergies in people with hypersensitivity to insect bites, but that’s unlikely.

The venom is, however, deadly to other insects. When attacking its prey, the Hornet Robberfly will inject a lethal cocktail of neurotoxins and proteolytic enzymes designed to paralyze the prey and liquefy its internal organs. The fly will then use its hypopharynx to slurp the resulting fluids, providing the fly with important nutrients.

4. Scary-Effective Combat Abilities

The Hornet Robberfly is a feared predator in the insect world due to the fact that it can subdue, kill, and feed on large prey. The Robberfly can kill insects larger and even more dangerous she is, including grasshoppers, bees, wasps, and even dung beetles, despite their almost impenetrable exoskeleton.

Nothing can withstand the fly’s powerful proboscis and lethal venom leading to almost immediate paralysis and death. Combine these abilities with the fly’s hornet-like appearance, and you can see why this creature is so feared in the insect world.

5. Death Comes by Air

The Hornet Robberfly is an extremely agile flying insect, capable of stalking, catching, and killing its prey mid-air. The fly can only achieve this via its outstanding ability to assess distance, change its position abruptly in mid-flight, and crash onto its suspecting victim out-of-the-blue.

Once the Hornet Robberfly has locked onto its prey, the fly will engage in some short dogfight, allowing it to get close fast. The fly will use its spiky legs to grab hold of its victim and inject its venomous cocktail. This will disable the unfortunate insect fast, causing both attacker and victim to fall to the ground, where death will occur shortly.

The Robberfly’s ability to hunt during flight makes it even scarier than how it already appears at first sight.

6. Like Mother, Like Baby

The Robberfly larvae share their parents’ voracious attitude and predatorial instincts. The Robberfly will lay the eggs in cow or horse dung, where the larvae will feed on any organisms living there, primarily dung beetle larvae. These will provide the Robberfly larvae with vital nutrients to withstand their growth over the years.

Yes, years. Apparently, the Robberfly larvae will remain in this state between 1 to 3 years, after which they will pupate and turn into adults. The adults don’t live long, maybe only several weeks, since their primary goal is to mate, after which they can die in peace.

7. Hunter-Specific Anatomical Setup

Everything about this fly screams predatorial species. The Robberfly has developed a variety of offensive mechanisms, turning the fly into a deadly predator. These include:

  • Spike-filled legs – The fly’s legs are covered in thorns which aid the fly in catching its prey. These thorns function similarly to python teeth. They grow at an angle, allowing the fly to stick to its prey and prevent it from escaping.
  • Slim abdomen – The Robberfly displays a segmented and slim abdomen, improving their aerodynamics and lowering their weight.
  • Quasi-omnidirectional eyes – This is a pretentious construction for “the fly can see everywhere at once.” The Robberfly’s compound eyes allow the insect to see above, in front, and behind it at the same time, giving it a massive advantage over its prey.
  • Using halteres – These are remains of vestigial hindwings which are present in a variety of flying insects. They are small appendices that aid the fly to stabilize its position in space, especially during fast flight. In other words, halteres provide the fly with additional accuracy when hunting its prey in mid-flight.
  • Its appearance – The Robberfly’s appearance functions as a deterrent against potential predators who will take the fly for a hornet. This ingenious camouflage also has unexpected results because it can confuse some of the fly’s prey. Wasps, for instance, may take the fly for a fellow wasp and fail to avoid its incoming attack until it’s too late.

All these specifics paint the Hornet Robberfly as the ultimate tiny predator with an impressive success rate and a rather disgusting life cycle.

8. Subpar Flying Capabilities

After praising the Robberfly for its impressive mid-flight hunting, this point may seem out of place. Yet, it’s true. For instance, the Robberfly only possesses one pair of thin and weak wings, compared to wasps. This makes it less effective at flying over longer distances.

With short stamina and only one pair of wings, the fly can’t move across vast distances and won’t be able to pursue its prey too long. This faulty feature counterbalances the insect’s otherwise pristine predatorial profile. Now, its prey has a chance of evading its death grips.

9. Risky But Clever Behavior

The Robberfly will spend most of its time in the open, waiting for passing prey to hunt. This behavior is atypical for most insects, since this makes them vulnerable to predators. Most insects will either hide, display flashy ‘I’m poisonous’ bodies, or develop ingenious camouflage, rendering them invisible.

The Robberfly doesn’t have any of these perks. So, it evolved its own camouflaging mechanism.

Instead of making it invisible, its ‘camouflage’ turns it into a more dangerous predator than it really is. Most potential predators will see the fly as a hornet and turn the other way, allowing the fly to survive.

10. A Bearded Insect

The Robberfly will sometimes hunt larger and more dangerous prey that won’t go down silently. It may kick, scratch, and attempt to bite, and the fly risks getting hurt. Evolution has provided the fly with a protective moustache and beard, covering its mouthparts to prevent injuries.

Similar hairs cover the fly’s thorax for the same reasons.


The Hornet Robberfly is an amazing creature and a proficient predator that you are rather unlikely to meet or recognize in the wild. To add a few more interesting facts:

  • The Hornet Robberfly ranks as an endangered species due to the destruction of its natural habitat and agricultural development
  • We haven’t observed Robberfly larvae feed, so we can only guess what they’re eating
  • Robberfly saliva kills invertebrates instantly but it’s mostly harmless to humans
  • Robberfly never inject venom into humans; the mild pain and irritation resulting from its bite relate to its saliva
  • The adult female Robberfly will display a stinger-like structure at the rear of its abdomen, making the insect resemble a hornet; this is actually its ovipositor
  • Current efforts are being made to preserve the Hornet Robberfly
Insects   Updated: January 17, 2022
avatar Welcome to Insectic, a blog to learn about insects and bugs. I'm Richard, and I've created this website to share my experience, knowledge, and passion with others.

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