Rosa Rubicondior: Unintelligent Design - An Arms Betwen The Sexes!

Male flies' better vision called the females' bluff | University of Gothenburg

When dance flies mate, females make themselves more attractive by swallowing air and laying their hairy legs along their bodies to look like they are full of eggs. New research shows that the males have developed better eyesight, probably to detect the deception.

As I showed in my books, The unintelligent Designer: Refuting the Intelligent Design Hoax and Unintelligently Designed Arms Races: How Nature Refutes Intelligent Design, the natural arms races that are ubiquitous in nature make no sense as the work of an intelligence. It is simply not an intelligent act to have an ultimately pointless arm race with yourself.

Arms races happen because one side doesn't know the other side's next move but falling behind could be ultimately fatal. Both sides have no option but to use the 'Red Queen strategy' of running ever faster just to stand still. It makes as much sense as playing poker with yourself. As the act of an intelligence, it would mean the designer sees the solution to yesterdays' problem as today's problem to be solved. It probably tells us a great more than they might wish us to know that creationists think this is a sign of supreme intelligence.
The latest such arms race to be revealed by science makes even less sense from an intelligent design perspective if that's possible. This one is an arms race between the sexes in an order of insects known as dance flies and is the result of the two different strategies the males and females use to ensure they get the best mate and so produce the fittest offspring.

Dance flies are (mostly) predatory flies that kill and eat other insects. To attracts a female, males perform a dance with other males in a flying display. The females attract a male by showing him her abdomen in full of eggs and she is ready to be inseminated. The male then pursues the female and presents her with a dead insect as food. She then allows him to mate with her. They will then go off and repeat the mating rituals so both will mate with multiple partners. The female then lays her fertilised eggs in damp soil where they hatch and live as larvae and pupa until ready to hatch and repeat the cycle.

It is in the females reproductive interest to attract the fittest males and she does this by flying in front of him to display a large body full of eggs, while the male concentrates his efforts of pursuing the female most likely to produce a large batch of eggs, and presenting her with a nutritious meal in return for mating with her.

What information do you have on the dance flies of the subfamily Empidinae (Diptera: Empididae)? Dance flies of the subfamily Empidinae (Diptera: Empididae) are a fascinating group of predatory and often lekking flies known for their complex mating behaviours, including gift-giving and elaborate aerial displays. Here are some key details:

Morphology & Identification

Small to medium-sized flies, typically 2–10 mm long.
Slender bodies with long legs and prominent proboscises adapted for predation.
Antennae usually short, with a three-segmented structure.
Wings are well-developed, often held roof-like over the body when at rest.
Ecology & Behaviour

Predatory Nature: Both larvae and adults are typically predatory, feeding on other small insects. Some species, however, are nectar feeders.
Mating Swarms & Courtship Gifts: Many species exhibit nuptial gift-giving, where males present prey items (or sometimes inedible objects wrapped in silk) to females during courtship. This behaviour influences female choice and increases male mating success.
Aerial Mating Displays: Males often form swarms where they perform acrobatic displays to attract females.
Habitat: Common in moist environments, including woodlands, meadows, and near water sources.
Reproduction & Lifecycle

Eggs are laid in soil, rotting vegetation, or near water.
Larvae are predatory or saprophagous (feeding on decaying organic material).
Pupation occurs in the soil or within decayed plant matter.
Adults emerge seasonally, often in spring and summer.
Notable Genera

Empis - Large genus known for elaborate courtship behaviour.
Rhamphomyia - Includes species where males form leks and exhibit extreme sexual dimorphism.
Hilara - Some species create balloon-like silk packages to deceive females into mating.
Evolution & Phylogeny

Empidinae is a subfamily within the Empididae, which is part of the larger superfamily Empidoidea.
Fossil records suggest their presence since the Cretaceous, with early forms likely predatory.
Their courtship behaviours are considered examples of sexual selection and evolutionary arms races between male display traits and female choice.

However, this strategy has created an opportunity for females to get fed by males by fooling them into thinking her eggs are ready to be laid. In most species, the female rarely hunts and relies on this subterfuge to get food while her eggs are developing inside her. She does this by positioning her legs to make her body look larger (and so full of eggs) and by being more hairy or scalier to enhance this appearance; in some species the females even have inflatable sacs in their abdomens.

But it is clearly in the males' interest to see through this subterfuge so he can concentrate more of his effort in catching prey to feed to females who really do have an abdomen full of eggs and who are likely to mate with fewer males before laying them, increasing his chances of fathering the next generation of dance flies.

Hence there are two competing strategies at work here - the females in fooling the males by being more ornate and with leg positioning in flight, to get free food, and the males in seeing through the subterfuge - which requires higher visual acuity.
The evolutionary consequences of this, as a team of researchers from the University of Gothenburg, Sweden have shown is that there is a correlation between the species of dance fly with more ornamentation (hairiness) in females and the visual acuity of males. This finding is the subject of an open access research paper in the journal Evolution and a news item from Gothenburg University:

Male flies' better vision called the females' bluff
With bloated bellies and hairy legs, female flies try to look bigger to get food from courting mates. But male flies, in turn, have sharpened their eyesight to call their bluff. A new study by researchers from the Universities of Gothenburg and Stockholm suggests that this is an ongoing evolution where both sexes try to outsmart each other.
For the first time, researchers have been able to show that also males can develop traits that help them pass on their genes despite the manipulative adaptations of the opposite sex. In different species of dance fly, there is a clear correlation between how richly decorated the female flies are and how large the eye facets are on the males. The researchers interpret this to mean that the males needed to develop better vision to find the optimal female in the swarm.

Dead insect as a nuptial gift

We almost always see enlarged eye facets in male flies in those species where the female flies have developed hairy legs. Therefore, we dare to assume that there is a connection.

Luc F Bussière, co-corresponding author
Biological and Environmental Sciences
Faculty of Natural Sciences
University of Stirling, Stirling, UK And Institut för Biologi och Miljövetenskap
University of Gothenburg, Göteborg, Sweden.

The female receives a dead insect as a gift from the male during mating. The gift provides the female with the necessary protein to produce eggs. If the male arrives empty-handed, he is rejected.
Photo: Tom Houslay

There is an intricate interplay that takes place when the dance flies mate. The flies only fly for 1–2 weeks in their life cycle and that is when they have to reproduce by laying eggs that become fly larvae. To increase the chance that their genes will be passed on, male flies look for females that appear to have the most eggs. When mating, the male fly brings a gift, usually a dead insect, which he gives to the female. The female rarely hunts on her own and relies on the protein from the insect to produce eggs. Without an insect for the female, the male is usually not allowed to mate.

So how does a younger female fly without eggs attract male flies to get food supplies?

We see that the females have different characteristics and tricks to imitate being fecund. They swallow air that fills their abdomen, and to look really big when they swarm, they have developed hair on their legs and their wings are bigger and darker.

R Axel W Wiberg, co-corresponding author
Biological and Environmental Sciences
Faculty of Natural Sciences
University of Stirling, Stirling, UK and Department of Zoology
Stockholm University, Stockholm, Sweden.
The fact that animals imitate, behave and have appearances to fool the opposite sex is nothing new. Previous research on flies has also shown that male flies prefer a plump female fly to a skinny one when mating. But now scientists have discovered that male flies have sharpened their eyesight to avoid being fooled.

Sexual play evolves the species

By capturing male flies and measuring their eye facets, the researchers discovered that the facets on the top of the eyes were larger than those on the underside in the males of some species. Since the male fly approaches the female from below during mating, the researchers believe that the eyes have evolved to determine whether the female is truly full of eggs, or just faking it.

This sexual play may force an evolution of the species. For generations, male flies with the largest facets have been favoured in mating and their genes are passed on. We see this as an evolutionary system where the development of different traits in male and female flies has been alternating.

Luc F Bussière.

Female flies of the different species in the study have different characteristics, some have only slightly darker wings, others have both darker wings and hairy legs, and can inflate their abdomen by swallowing air. These traits did not appear all at once, but probably as the male gets better and better at seeing past the bluff.

What will be the female's next move?

Perhaps the female develops new traits that make it harder for the male to judge her size. Or she may develop entirely new strategies to gain an evolutionary advantage. For example, we see that in the species with the largest facets in the male, the female also has slightly enlarged facets – but on the underside of the eye. We don't know what this means, but perhaps it helps the female to see an approaching male more quickly and thus find an advantageous position in the swarm.

R Axel W Wiberg.

The life of a dance fly

Adult dance flies lay eggs during the summer which then hatch into predatory larvae in the soil. The larvae hunt and eat other organisms and in the northern hemisphere are likely to become pupae before winter. In spring, the pupae complete their development and become flying insects; flies.

Flies emerge at different times during the summer, for most species the flight period is only a few weeks at most. During this time, males and females gather in swarms to mate. In almost all of the dance flies from the subfamily included in the study, the males bring nuptial gifts to the mating swarm in the form of insects. During mating, the female feeds on the male's gift while the male inseminates her. Mating is repeated several times with different partners.

Once the female has mated and eaten enough meals from the males, she can lay several eggs in the soil that will be the start of the next generation.

Publication:
R Axel W Wiberg, Rosalind L Murray, Elizabeth Herridge, Varpu Pärssinen, Darryl T Gwynne, Luc F Bussière,
Sexually antagonistic coevolution can explain female display signals and male sensory adaptations
Evolution 78(12) 1 December 2024, Pages 2006–2016, https://doi.org/10.1093/evolut/qpae133

Abstract
The prevalence and diversity of female ornaments pose a challenge to evolutionary theory because males should prefer mates that spend resources on offspring rather than on ornaments. Among dance flies, there is extraordinary variation in sexual dimorphism. Females of many species have conspicuous ornaments (leg scales and inflatable abdominal sacs). Meanwhile, males of some species have exaggerated regions of their eyes with larger ommatidial facets that allow for regionally elevated photosensitivity and/or acuity. Here, we conduct a comparative study of these traits using both species descriptions available from the literature, as well as quantitative measures of eyes and ornaments from wild-caught flies. We show a conspicuous covariance across species between exaggerated male dorsal eye regions and the extent of female ornaments: species with highly ornamented females have males with more exaggerated eyes. We discuss this pattern in the context of competing hypotheses for the evolution of these traits and propose a plausible role for sexually antagonistic coevolution.

R Axel W Wiberg, Rosalind L Murray, Elizabeth Herridge, Varpu Pärssinen, Darryl T Gwynne, Luc F Bussière,
Sexually antagonistic coevolution can explain female display signals and male sensory adaptations
Evolution 78(12) 1 December 2024, Pages 2006–2016, https://doi.org/10.1093/evolut/qpae133

Copyright: © 2026 The authors.
Published by Oxford University Press for the Society for the Study of Evolution. Open access.
Reprinted under a Creative Commons Attribution 4.0 International license (CC BY 4.0)

It probably tells us a great more than they might wish us to know that creationists think this sort of lunacy is a sign of supreme intelligence, but it doesn't take a genius to understand that having an arms race with yourself, is not a sign if intelligence at work, but exactly the opposite - a sign of mindless, unintelligent process at work.

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