Towards Freedom

In May 2012, I spent a few hours photgraphing the mating ritual of two leopard slugs. Below are pictures and explanations. If you want meta data specifications about the picture, right click on it and select Image Properties.

The two individuals are the leader:

and the follower:

When a leopard slug wishes to mate, it communicates the fact chemically through its slime trail to any others who might stumble across it. As simultaneous hermaphrodites (an individual is both male and female), they are not choosy about their partners. When another slug finds the trail it will, if it also feels like mating, follow. Once it catches up with the originator it nibbles on its tail to announce its presence and intentions. The nibbled, having been alerted, begins a search for a location few other slugs would ever venture to. Thus, at a rate of ten or perhaps fifteen centimetres per minute, one of the most extraordinary rituals to be found anywhere commences.

Both of these slugs are residents of our woodpile. I'd seen the leader (upper right) several times before. It is easily identifiable by its relative lack of spots. The follower was new to me. Having watched Sir David Attenborough's BBC series "Life in the Undergrowth" where the mating ritual is shown, I immediately knew what was going on when I saw these two slugs behaving this way. I had my PowerShot camera and a light with me, but I knew the ritual could take several hours to complete. I rushed inside to stock up on batteries. When I emerged a few minutes later with full pockets, the slugs had moved all of a half metre or so. The leader was crawling along with great care, making sure to thoroughly examine everything it came into contact with along its path. Particular attention was paid to objects that seemed to project upward, however short they might be.

On occasion, the follower would lose the leader's tail and become lost. Remarkably, when the leader noticed this happening, it would stop and hold its position to give the follower a chance to catch up again.

Once the leader felt another nibble on its tail, the quest would resume.

Unfortunately for the pair, nothing they came across in the woodpile seemed interesting enough to prompt them to move to the next stage of their ritual. It was even more distressing for me because I'd been hoping I wouldn't have to follow them too far!

They went straight into the forest beyond our fence. An overenthusiastic beetle got into the spirit of things and tried to latch onto the train here before remembering it wasn't a slug.

I climbed over the fence and joined them in the forest. They continued to investigate everything that promised to go upwards with the exception of cedar trees. Perhaps they are uncomfortable to leopard slugs?

At last, after more than two and a half hours, they found a fallen alder branch that leaned against a cedar tree. The pair are not easy to spot in this shot. The leader is at the base of the branch and the follower is on the left of the frame.

Nowhere to go but up! Phase two of the ritual kicked off.

They came to a fork in the branch and chose the path that took them still further up. By this time they had been climbing for about ten minutes.

When they discovered their branch lead into a cedar tree, they were less than pleased! They spent a long while circling around, trying to find a way to get past it, but there was none. They stayed there for the better part of an hour before they gave up. The leader headed downward again. I thought they might be ready to call the whole thing off, seeing as how they'd already spend nearly four hours searching for the right spot.

Just as I was starting to realize how sleepy I had become, the leader suddenly swung upwards again. It became apparent that while they hadn't found exactly the place they were looking for, they weren't about to give up either! Phase three began in what must have been an awkward spot.

The two coiled around one another like snakes and loosened their grip on the branch.

Then they let go altogether and slid into thin air, hanging by a rope of thick slime!

This is why the slugs had been looking for something to climb for so long. They mate aerially suspended and require a certain amount of height to do so. How they know how much is enough I have no clue! Ideally, they would probably have preferred a horizontal branch or other overhang to drop from. In its absence, they chose to make the most of the branch they had.

Having descended far enough (they were still a good metre and a half above the forest floor), they commenced phase four of the operation.

Each slug's male reproductive organs are housed just behind their head on their right side. These are everted from their genital pore and snake downwards.

Like their bodies, they entwined their reproductive organs once fully extended.

These fanned out to form a blue, flower-like structure over an orb where the transfer of sperm took place. They remained in this posture for some nine minutes, spinning slowly on their thread.

With phase four complete, the fifth and final phase started. Perhaps the most tricky task of all was disentanglement. Remarkably, they managed it in only a couple of minutes!

Now unwound, they retracted their genitals again. Their thoughts then turned to unravelling their bodies!

That task took several minutes. Once complete, the leader once again took up its position in front and hauled itself back up the slime rope.

It didn't take long for the follower to latch on.

Safely back up in the tree, their four and a half hour long enterprise came to an end. Of course, each still had to find a safe place to lay eggs, but by that time I thought I had better turn in and said my farewell. That wasn't the last I saw of them, though! The next day, the follower was happily sliming its way around the woodpile again. Two days after that, the leader turned up too. Evidently despite their great adventure (at least seven or eight metres of travelling), they still considered the woodpile their home. Perhaps some of the little leopard slugs we see next year will be theirs!