Eight arms, three hearts, and even nine brains. Is there no end to just how extraordinary these cephalopods are?
Well, perhaps unsurprisingly, their reproduction methods continue the trend and are also fascinating.
We’re going to dive into the natural world of octopus mating by looking at the male and female reproductive systems, including finding out about the astonishing male octopus mating arm.
We’re going to discover precisely how octopus reproduction works and finish by checking out the unbelievable detachable octopus penis used by the pelagic argonaut octopus.
Ready? Let’s jump into wild sex and the octopus!
How Does an Octopus Mate?
As we look at how do octopus mate, we’re going to see that it’s almost always a once-in-a-lifetime experience.
Almost all octopus species lead solitary lives and spend their time looking for food and staying safe from predators until it is time to reproduce.
So, as the octopus is typically a loner, let’s start by considering how they find a partner and when they do it.
Do Octopuses Have a Breeding Season?
Keeping in mind that there are around 300 different octopus species, we’re generally going to be talking about the one that’s been studied most by scientists, the common octopus (Octopus vulgaris).
This species typically lives for about three to five years and will reproduce once they’re reached adulthood.
The time of year that the common octopus tends to reproduce appears to depend on the location and perhaps is related to sea temperatures, light, and nutrition.
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For example, a 1972 lab study concluded that “O. vulgaris breeds throughout the year, at least in Bahamian waters.”
On the other hand, a different study of the spawning season off the northwestern coast of Africa suggested that “There are two spawning seasons, one in spring (May-June), and the other in autumn (September), at least in the Cape Blanc region.”
As octopus breeding relies on becoming sexually mature and finding a suitable partner, it seems that so long as the conditions are conducive, reproduction can take place most of the time.
Indeed, in tropical and subtropical waters specifically, eggs have been observed being laid all year round.
However, octopuses that live in cooler water appear to have more consistent breeding patterns.
How Does an Octopus Find a Mate?
Once an octopus has reached adulthood, it forgets its solitary lifestyle and starts to look for a partner.
Whether you’re a pelagic octopus living in the open ocean or one that dwells on the coral reef, finding a partner just as adept at hiding as you are could be tricky.
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In most species, the male mollusc seems to spend most effort tracking down a partner. Females are typically less active but may produce special chemicals that the male can use to track their location.
Once males and females have found each other, scientists believe they both use their acute sense of sight to help decide if the other is a worthy partner.
Males appear to look for the largest female they can find as they will produce the most eggs, leading to a greater chance that his genes will live on.
The male will produce complex flashing patterns across his skin and change his body shape to impress a female using his color-changing pigment cells.
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Females will also judge the size of the male’s ligula, which is the erectile part at the end of the male’s hectocotylus (aka the penis arm – more on this shortly).
Reproduction will cautiously begin once both males and females are convinced it’s an appropriate match.
The Male Octopuses Reproductive Organs
Everyone knows that octopuses have eight arms, right?
But did you know that incredibly, one octopus leg is also the males penis?
Female octopuses can get a little bit aggressive during reproduction. In fact, they can exhibit cannibalism and may kill and eat their partner during or after sex.
For this reason, scientists believe that the male octopus has evolved a modified arm called the hectocotylus that allows them to deliver their sperm from as safe a distance as possible.
So, what does an octopus penis look like? Generally, it seems like the other arms, but with some modifications.
The hectocotylus penis has a central groove called a calamus which holds the sperm packet (the spermatophores). It’s often the third right limb of the octopus.
At the tip of the modified arm, there is a spoon-shaped depression with modified suckers and a section of erectile tissue known as the ligula.
When the male is aroused, like humans, the ligula tissue fills with blood and becomes rigid. As we’ve already mentioned, the male will use the ligula’s size to convince the female that he’s an appropriate partner.
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The rigid modified tip also gives the stiffness needed for the male to guide the arm into the female’s mantle when reproduction has started.
How long is an octopus penis depends on the species itself. Often they’re 10-20 percent longer than the other arms.
Do male octopus have balls? Yes, they have one, although you won’t see it as it’s hidden inside the mantle.
The octopus testicle is oval in shape. In addition to the rest of its reproductive tract, when the male reaches maturity, it produces sperm in packets stored in the hectocotylus, ready to be delivered when the time comes.
The Female Octopuses Reproductive Organs
The female octopus’s reproductive organs are slightly less unusual than the male’s modified arm. However, they are no less essential.
Females have a single ovary that has two oviducts, each with an oviducal gland, that open into the mantle cavity. When spawning occurs, the sperm will swim up the oviducts to fertilize the female’s eggs.
How Do Octopus Reproduce?
Once two octopuses have found each other and partner selection is completed, octopus reproduction can begin.
The male needs to stay on his guard during the process. The female might decide that he may make a good meal, or a competitor may come along and try to steal his partner.
It’s actually fairly common for females to end up mating with more than one male, and they can store multiple sperm packets until they spawn.
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A favored tactic for some males to stay protected from an aggressive partner is to set a den of their own next to the females so they can try and use their long modified arm to deliver their sperm without leaving their shelter.
When sex begins, the male uses his hectocotylus to carry the sperm to the entrance of the female’s oviducts.
To reach the duct, the male will push his erect ligula into the female’s mantle and hold it there until all his spermatophores have been transferred to the pallial cavity.
Before the sperm is delivered, some males cunningly use the ligula tip to remove sperm already given by competing males.
The octopus sperm arm can take as long as four hours to deliver the sperm packets to the mantle cavity, so perhaps it’s no wonder that the female’s mind sometimes moves on to food!
What Happens After Octopus Mating Is Complete?
After mating is complete, the male moves on, having played his part in continuing his lineage, and he will begin the senescence process leading to his death.
The female octopus will store the sperm until her eggs are ready to be fertilized. At this point, the eggs will pass through the oviducal gland to meet the sperm swimming the other way.
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When the fertilized eggs are ready, which can be as long as forty days after mating, the female will attach strings of thousands of them to an appropriate substrate and guard them until they hatch.
During the process, the female will not leave the eggs alone and will spend her time protecting them from predators and cleaning and aerating them with fresh water. It can take as long as ten months in coldwater octopus species before the eggs are ready to hatch.
After the eggs hatch, the female also moves on to die.
The exception is the larger Pacific striped octopus (LPSO) which can reproduce multiple times during its two-year life.
The eggs hatch as paralarvae which will float in the water column as plankton. They eventually settle on the seabed and quickly grow into adults.
Female Octopuses are Sometimes Cannibalistic After Mating
After mating has taken place, it’s pretty common for the female to kill and eat the male.
Often, after mating is complete, even with the long reach of his one arm, the female will kill the male and take his body into her den to eat.
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While it may not be a pleasant end to the male’s life, as he will die anyway, he can at least present his partner with a final boost of protein before she has to spend weeks or months tending the eggs.
How is Giant Pacific Octopus Reproduction Different?
The giant Pacific octopus (Enteroctopus dofleini) has a five-year lifespan. The female normally becomes sexually mature between two and three years.
Scientists have observed these octopuses mating both side by side and with the male on top, and the mating process takes between three and four hours.
The giant octopus’s two spermatophore packets can measure as long as one meter (three feet) and contain as many as seven billion sperm. They’re so long that delivered spermatophores can sometimes be seen sticking out of the female’s mantle pouch as they’re too big to fit inside fully.
Once ready, the female lays between ten and seventy thousand eggs and incubates them for six to seven months.
How Does an Argonaut Octopus Mate? (The Octopus With the Detachable Penis)
The argonaut (genus Argonauta) is a group of special pelagic octopuses.
Male argonauts are very small and only a couple of centimeters (three-quarters of an inch) long. Meanwhile, fully grown females of the same species can be up to 30 times larger.
The male argonaut has developed an octopus detachable penis to manage the mating process.
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When he finds a suitable female, the male can deliver his hectocotylus in several ways.
He may attempt to hand over the spermatophores in the usual way by penetrating the female’s mantle. When this is done, the penis will detach as it makes its delivery.
Alternatively, the male may load up his arm and then detach it before even coming in contact with the female argonaut’s body.
He can then literally pass it to the female so she can fertilize herself with it, or he may even let the detached penis arm swim over to the female, under the control of its mini-brain.
The detached arm will crawl under the gill cavity until the female is ready to use it. Scientists have observed female argonauts with multiple separate arms from several mates sitting discarded in her gills.
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The female argonaut is the only cephalopod with a distinctive thin shell called a “paper nautilus,” which she makes from calcite secretions.
She will use this shell as a surface in which to lay her eggs. The egg case resembles the shells of extinct ammonites, and it’s thought that the ancestors of the argonaut may have used these before evolving to make their own shells.
The female will continue to live inside the shell, drifting in the ocean until the eggs are ready to hatch.
The female argonaut will release the fresh larvae from her shell at night by using her gill cavity to squirt them out into the water column.
The Male Dies Soon After the Detachable Penis is Removed
Scientists have never found a live male argonaut without its detachable arm, so they believe it dies more or less as soon as it can be removed.
Conclusion
The incredible way that the octopus penis arm has evolved and is used gives males some hope that they can deliver their genes successfully to the female without first ending up a meal themselves.
The tiny male argonaut octopus has taken this one step further by making his penis detachable.
He can either hand the one arm over or even leave the detachable penis to swim across to the female to deliver his spermatophores.
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Once a solitary octopus has found a mate for courtship and successfully reproduced in almost every species, its life is basically over. Be sure to check out our article that tells you why do octopuses die after mating.
British-born Dan has been a scuba instructor and guide in Egypt's Red Sea since 2010.
Dan loves inspiring safe, fun, and environmentally responsible diving and particularly enjoys the opportunity to dive with sharks or investigate local shipwrecks.
When not spending time underwater, Dan can usually be found biking and hiking in Sharm's desert surroundings.
What use is a hectocotylus if you die soon after it’s detached anyway?