Banana Slug Facts: They Bite Off Genitalia After Mating

Did you know that banana slugs eat the organ of their partner after mating? Besides this weird habit, they also have many unique features that make them stand out in the forest ecosystem. So, get ready to discover some interesting facts about these yellow slimy creatures!

Banana slug
Scientific name: Ariolimax
Phylum: Mollusca
Class: Gastropoda
Order: Stylommatophora
Family: Ariolimacidae
Genus: Ariolimax

1. Banana Slugs look like a banana 

The banana slug is the second-largest land slug in the world and the largest in North America. The world’s biggest slug has a size of 10 inches. However, they are commonly from 6 to 8 inches in length. 

Its name is derived from its resemblance to a ripe banana, with bright yellow being the most common color. This species can also come in different colors, from brown, white, and green color or with black spots. The ones with more spots will have a darker color than the ones with few or no spots. The color of banana slugs varies according to their age, health, nutrition, hydration, and environmental circumstances. 

A spotted banana slug

Although these slugs have a bright yellow color at times, they are well camouflaged in their natural habitat. The forest floor in their range has yellow leaves and needles, which helps them blend in.

Banana slugs, like other slugs, have 4 tentacles to detect their surroundings. A pair of larger upper tentacles on their heads have tiny black dots (eyes) at their ends. Those “eyes” are used to detect movements and lights. Their smaller and lower tentacles in front of their “face” are used for feeling and smelling. 

Those tentacles can move separately and retract swiftly. If a tentacle is lost due to predation or mishap, the slug has the ability to regenerate it. 

A banana snail

Located on the right side of a banana slug’s head are three distinct openings. The pneumostome, which banana slugs use to breathe, is the most noticeable. Similar to a whale’s blowhole, the pneumostome can be opened or closed, allowing air to reach the lungs or preventing drowning or dehydration during severe weather.

The other two openings are smaller in size and serve different functions: the anus and the gonopore, which are involved in reproduction.

There’re about 5 banana slug species, including the Pacific, California, Southern Pacific, slender, and Button’s banana slugs. 

2. Diet

Banana slugs have a diverse diet, consuming living and decaying plants, moss, lichens, animal waste, and even carcasses. They especially enjoy mushrooms, which are plentiful in their moist habitat.

To eat food, these giant slugs use a long tongue having a ribbon shape. This tongue is covered by up to 25000 tiny teeth. This mouth part is known as radula.

They eat those things and then convert their food into nutrient-rich waste that enriches the soil. That’s why these decomposers are critical species in their ecosystem.

These species have quite a few predators such as Pacific giant salamanders, foxes, millipedes, northwestern garter snakes, newts, beetles, crows, porcupines, and ducks.

The slime makes them hard to taste and swallow

To protect themselves, the yellow slugs have developed effective defense mechanisms. They shrink into a ball, making them too large to swallow. At the same time, they also increase their slime production to make them more sticky.

Additionally, they use their slime to numb the predators’ tongue as mentioned above. However, some predators counteract this by rolling the slugs in the soil to dilute the mucus before putting them into their mouths.

3. Habitat

In the Pacific Northwest, from California to Alaska, banana slugs locate on the moist, temperate floors of coniferous forests. While California, particularly the Santa Cruz Mountains, is a hot spot for this species, some of them are found along the coast of San Diego County and on select damp western slopes of the Sierras.

4. Their Slime help them breathe, move, and chase away predators 

Banana slugs, like all gastropods, are mostly made up of water and require moisture to survive. They secrete a layer of mucus, or slime, to cover their body to keep themselves hydrated. 

The slugs create microscopic dry grains of mucus that interlink to form a mucin chain. When this chain encounters water, it expands to over 100 times its first size. This generates a sticky mucus that provides maximum lubrication with minimal effort. 

Due to this need for moisture, banana slugs require a damp environment to thrive. 

The slime not only helps the slugs avoid dehydration but also aids movement and provides protection against sharp edges. These species move by contracting and stretching their one foot. Their slime aids slug adhesion and boosts suction, allowing them to move along the surfaces and even upside down.

If a slug climbs too high up a tree, it can descend quickly by secreting a slime cord and sliding down. When moving, plant materials and debris stick to the slug. Its mucus assists in gradually propelling everything to the tail end of its body. The species can turn back and feed on all those materials. 

The slime also acts as a defense mechanism against predators by slowing them down and potentially causing harm. The mucus contains poisonous chemicals. It can numb the tongue and throat of a predator that tries to consume the slug.

Moreover, the slime serves as a means of communication among slugs. They leave chemical messages through their mucus, which is vital for homing and mating behavior. During mating season, the messages entice potential mates to follow as the slugs add pheromones to their slime.  

5. Behavior

Banana slugs spend their solitary lives wandering the jungle at night for meals. However, when humidity levels permit, they venture out during the day as well. 

During periods of heat and dryness, they enter a “summer sleep” known as estivation, similar to hibernation. They bury themselves in leaf litter, secrete slime to cover their bodies, and wait until the conditions are better. They also hibernate in the winter.

Dormant banana slug

These big slugs are among the slowest species in the world. They move at roughly 3-4 inches per minute, with the fastest speed of over 6.5 inches per minute.

They can float and swim by bending their bodies sideways.

6. They have male and female organs

Banana slugs are hermaphrodites, which means they own both female and male reproductive organs. While self-fertilization is possible, these slugs typically engage in cross-mating. They will both exchange their sperm during an intercourse. In this way, the eggs of both slugs can be fertilized. This unique trait increases the likelihood of successful reproduction, particularly in low population densities.

What is special about these huge slugs is their exceptionally long penises. It can measure up to their entire body length when erecting. In fact, the species Ariolimax dolichophallus is aptly named after this impressive genital feature, with “dolichophallus” meaning long penis.

7. They eat their mate’s reproductive organ after copulation

Mating among banana slugs takes place throughout the year in their moderate climate range and can occur multiple times. The slugs utilize pheromones in their slime to entice potential partners.

To mate, the species start biting each other first, after which they intertwine to form a yin-yang shape. They then utilize their penises, which emerge from their head’s genital pore, to either take/receive/swap sperm. Each species will have a different mating ritual. 

For example, A. dolichophallus mates for about 4 hours, during which their penises intertwine. On the other hand, the reproduction of A. californicus only can last for only about 10 to 20 minutes, with a single penis participating. This means only the eggs of one slug are fertilized.

Following intercourse, one of the slugs proceeded to gnaw on the other’s penis with exceptional intensity. The penis was entirely severed within a few minutes. So, why do they do this?

From an evolutionary perspective, maximizing offspring production is a top priority for every organism. So, the females want to mate with as many males as possible. However, if a female has multiple mates, the chance that the male father her offspring is very small.  

Banana slug reproduction

As a result, males have created intricate tactics to make sure that their sperm wins over that of competitors. In the case of banana slugs, males sever their mate’s reproductive organs, leaving them unable to mate with other slugs.

These creatures can store sperm for extended periods to fertilize eggs. They lay a batch of 20-30 translucent eggs under leaves or logs. After a month, the eggs hatch and have no parental care. These 1-inch young have to live on their own. The lifespan of banana slugs can last for 7 years.



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