The stalk-eyed fly is one of the weirdest insects on earth. They are anything but ordinary, from their unusual appearance to their complex courtship rituals. Today, we’ll delve into the world of stalk-eyed flies and discover some of the most fun facts of their lives.
1. They are flies with eyestalks
Belonging to the Diopsidae family, the stalk-eyed fly is one of the most outstanding insects in the world due to its weird appearance. With elongated “eyestalks” that protrude from the sides of the head, these flies are distinguishable from most other flies species. The eyestalks end with the eyes, allowing for an increased range of vision.
There are over 100 identified stalk-eyed fly species, all of them are small to medium-sized. They often have a size of 0.15-0.45 in (4-12 mm) in length. Compared to other flies, their heads are relatively small and triangular in shape.
In many stalk-eyed fly species, males have significantly larger eyespans than females, a trait known as sexual dimorphism. The eyespans of stalk-eyed flies are even greater than their body length.
2. Males with large eyespan are preferable
In the stalk-eyed fly species, males with large eyespan have advantages. They are the favorite of females. There are reasons for this.
Research suggests that males with larger eyespans exhibit higher levels of fertility in comparison to those with smaller eyespans.
Moreover, a male’s genetic superiority is also indicated by a large eyespan. Males possessing “high quality” genotypes can exhibit large eyespans, even in situations with limited food resources. Conversely, males with “lower quality” genotypes have short eyespans under these conditions.
Females increase the likelihood of producing male offspring with greater stress tolerance and wide eyespans if they choose large eyespan males. This will increase their young’s survival.
3. Not stalk-eyed flies have eyestalk
As mentioned above, stalk-eyed flies are known for their long eyestalks, but not all members of the family possess this feature. For example, about 22 species of the subfamily Centrioncinae have regular appearance. It is the Diopsidae family that s most notable for their eye stalks, with every species possessing this trait, earning them the name “stalk-eyed flies”.
However, the eyestalk feature is not exclusive to the Diopsidae family. There are at least eight other fly families that have evolved this feature, including Drosophilidae, Platystomatidae, Periscelididae, Micropezidae, Richardiidae, and Tephritidae.
The difference between the true stalk-eyed fly and the other eye stalk fly with eyestalk is their antennae. Diopsidae members have antennae that grow from their eye stalks while other families have antennae on the head.
Additionally, both male and female true stalk-eyed flies have eyestalks, whereas only males from the other 8 families own this characteristic.
The stalk-eyed fly can be found across a vast area, spanning Europe, Southeast Asia, North America, and Southern Africa. Nevertheless, the majority of these flies are concentrated in the “Old World” tropics, specifically in Southern Africa and Southeast Asia.
These flies usually inhabit locations with low-lying vegetation and high humidity levels, often near flowing freshwater such as rivers and streams. At night, they tend to return to the same resting spot and cling to thread-like structures such as root hairs.
5. They fight with their eyes
Male stalk-eyed fly often stays in rainforests, perching on shaded tree trunks which they defend against rivals to use as a courtship territory. They may engage in a battle to mate with females.
Interestingly, these creatures engage in combat by colliding their eyes together in an unusual manner. It’s similar to how deer use their head protrusions to fight with other males.
These battles begin with a sizing-up competition, with the males measuring each other’s physical size and strength based on their head width when facing each other. If one of these flies determines that they are the smaller, it will withdraw early to avoid potential harm.
However, if this does not happen, an eye fight will occur. They may use their forelegs to punch, push each other, and use head-butting. The winner of this battle claims the territory and gains access to any females within the area.
6. Everything comes with a cost
Having large eyestalks may be advantageous for impressing potential mates or intimidating competitors. However, this comes with a price. This feature can attract unwanted attention from predators and make it difficult for them to navigate through narrow spaces.
However, despite these drawbacks, according to research, these flies are able to fly without difficulty due to compensatory mechanisms – the larger wings. Females do not have this advantage.
7. They twerk to defend
When the stalk-eyed fly faces potential predators, it engages in abdominal bobbing to ward them off. Their predators will find it strange to attack them. Additionally, the male flies use an aggressive approach by walking up to their predators and punching them. All of these aid in their survival.
Interestingly, the size of the male flies’ eye stalks did not affect their fate when facing predators. They are at the same risk as smaller eyestalk flies. In contrast, female flies with smaller eye stalks are much less capable of avoiding predators.
The main diet of the stalk-eyed fly includes fungi and bacteria that inhabit decaying animals and plants. The larvae, on the other hand, eat both fresh and rotting plants.
9. They are promiscuous
Stalk-eyed flies are known for their promiscuity. For instance, in the Teleopsis dalmanni species, both males and females can mate frequently throughout their long lifetimes, sometimes up to 10 times in one morning. Females may endure repeated matings in order to avoid harassment, but they can still reject undesirable suitors.
These insects follow a typical insect lifecycle: after mating, females lay eggs, which hatch into larvae and then transform into pupae. In the last 30% of larval development, the optic nerve of the fly larvae elongates and narrows, following the cuticle as it expands outwards.
When the adult stalk-eyed fly emerges, its eyestalks are floppy and inflated. The species must immediately breathe air and pump it via the ducts in their heads to expand its eyestalks, a process that occurs within 15 minutes. This enables the eyestalks to elongate while still pliable. You can see more details in the video below.
- Tracey Chapman, Andrew Pomiankowski and Kevin Fowler – Stalk-eyed flies https://www.cell.com/current-biology/pdf/S0960-9822(05)00754-2.pdf
- Erica Mcalister – The flies that use their eyes to fight for love… well, sex at least https://naturalhistorymuseum.blog/2016/10/28/the-flies-that-use-their-eyes-to-fight-for-love-well-sex-at-least-curator-of-diptera/