3 Unbelievable Examples Of Extreme Sexual Dimorphism

Sexual dimorphism is defined as "the condition where the two sexes of the same species exhibit different characteristics beyond the differences in their sexual organs." [1]

Humans are a good example of this; males are generally taller, hairier, more muscular and they fart a lot!

Pheasants are another, more extreme example of sexual dimorphism. The difference between males and females is quite impressive:

Peacock, on the right and peahen on the left (source)

But I am not here to talk about "regular" examples of sexual dimorphism that you are probably already familiar with. Instead, allow me to introduce you to some animals that have taken the condition to a whole new level!

1# Orgyia antiqua

The first animal on the list is Orgyia antiqua or the rusty tussock moth as it's commonly known. As you can see, it's nothing special, just another regular moth:

Male Orgyia antiqua (credit)

But wait! The photo above is from a male. What about females? Well, here's where things get interesting! Here's how a female looks like:

Female O. antiqua (credit)

Yes, the above is a fully formed female O. antiqua! Although not clear in the photo, the female has vestigial wings and is flightless. And her abdomen is really, really fat! After the pupa stage, the female spends her entire life attached to her cocoon waiting for a prince to come and mate with her.

Here's a side by side comparison of the two:

(credit)

Before moving to the next animal here's a video showing a female specimen. The difference between the two sexes is really astonishing!

2# Triplewart seadevil

Scientifically described as Cryptopsaras couesii, the Triplewart seadevil is an anglerfish found in all oceans. Females are about 30 cm long whereas males are only about 1 cm long! Males are essentially parasites, spending their whole life attached to a female, as shown in the scetch down below:

Triplewart seadevil with parasitic male attached (arrow) (credit)

Males have a rudimentary digestive system and a re literally incapable of feeding themselves. Once they reach adulthood, they have to quickly find a female to attach themselves otherwise they will die! This attachment is followed by a fusion of the circulatory systems between the two, with the male directly feeding on nutrients provided by the female's blood! The only role these guys have is to provide sperm. In case you wonder, a female may carry up to 8 "parasites" on her body. [3]

Female Cryptopsaras couesii (credit)

3# Bonellia viridis

True, the sexual dimorphism of the Triplewart seadevil is quite extreme, but it's no comparison for the sexual dimorphism exhibited by Bonellia viridis or the green spoonworm as it's commonly known. First, let's start with a photo of a female individual:

Female green spoonworm (credit)

Females, like the one depicted above, are usually 15 cm-long with round or sausage-shaped body. As for males, they are very rarely observed because they are only 1–3 mm long AND because they spend most of their life inside the organs of a female! A single female can host up to 85 males! Usually males settle into the pharyx and foregut for a while, eventually migrating when fertilization is necessary. [4,5]

As a sidenote, these guys have a really interesting lifecycle. When born, they are sexually undifferentiated and their sex is at some point determined by external, environmental factors (like the presence or absence of other bonellia worms) and not by internal genetic factors as is the case with most other organisms!

Here are two videos. The first explains the green spoonworm lifecycle and one showing a female specimen:

The End

So, these are the three most dramatic examples of extreme sexual dimorphism I happen to know. Do you know of any others equally weird? Let me know in the comments!

More Strange Animals

References & Further Reading

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