Banana Slug mating spiral.

Exceptions are usually just where space is too constrained.
Banana Slug mantle spots visible through eggshell — alongside hatchlings.

Compare the left hatchling's mantle spot with figures in the eggs.
Internal shell visible through the mantle of juvenile Banana Slugs.

Look for the cloudy shape beneath their mantle spot — also visible on those without. These lil' slimers are 44 days old.
12-Inch / 30cm Banana Slug

Banana Slugs are only documented elsewhere as reaching up to 10" (25cm)!
Clutch of Banana Slug Eggs
Banana Slug Mating Wounds

Holes indicated here in the tail and mantle.
Banana Slug penis upon mating separation.

Apophallation is the chewing off of the penis after mating — reported elsewhere with Banana Slugs as taking place ~5% of the time.
Sleeping Banana Slug

Homes being where they return for rest on more than one consecutive day.
Banana Slug nibbling during courtship.

Tastes like Banana!
Banana Slug suspended in a Scotch Broom shrub.

Banana Slugs often feed on both the leaves and flowers of this invasive shrub.
Banana Slug courtship chase.

The pursued may even whip their tail out of the way.
A plot of Banana Slug mating frequency over four months.

This was exceptional. ~1 hour is most typical.
Adult Banana Slug with hatchlings.
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Banana Slug Notes & Care

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Notes

Care

Despite their popularity, Banana Slugs (Ariolimax) aren't nearly as understood as many other gastropods — likely as their low temperature requirements and narrow distribution limit captive study.

Since 2022, I've observed Button's Banana Slugs (A. buttoni) almost daily along the Mendocino Coast, and in early '24 began caring for my first in captivity. While the following guide will focus on this experience and their nuances, it should at least loosely apply to any of the genus.

Wild yellow Banana Slug.

Notes

Based on Personal Observation

General Behavior

  • Semi-arboreal, as their daily rest is often split between ground level and heights of up to ~15' (4.5m). This tendency to alternate resting elevation continues in captivity — despite a static climate. Fully arboreal activity is also common in the wet seasons wherever elevated food is available — such as amongst Scotch Broom.
  • Rests on the ground are often a home, and they will chase away those that are found occupying it. Homes may eventually be abandoned if either the climate or food availability degrades.

Climate Tolerance

  • As ectotherms, temperatures have a direct impact on their metabolism, which in turn has a major impact on their rate of aging and activity. ~55°F (13°C) was found to correlate with their peak metabolic rate, as when maintained long-term, they mature the quickest and mate the most frequently.
  • An upper limit to comfort may be ~65°F (18°C), as ~68°F (20°C) is enough to wake an individual from rest and prompt a search for cooler temperatures.
  • Without a moist surface, signs of stress appear below ~65% RH, as slime production sharply increases and activity diminishes.

Age Markers

Banana Slug Age Markers

Reproduction in Captivity See Conditions

  • Sexual maturity is reached at ~5 months of age.
  • Mature individuals tend to court any conspecifics they bump into — including hatchlings. This involves persistent nibbling, which typically leaves scars and may eventually result in fully-punctured skin. If reciprocated, they focus on their partner's right flank until their gonopores align — otherwise, a chase ensues until either reciprocation or lost contact. Fleeing doesn't necessarily mean disinterest, as the pursued will occasionally return to their pursuer upon separation — suggesting overstimulation. Successful courtships ranged from ~30 minutes to as long as ~3 hours, and will typically conclude in a Yin-Yang spiral.
  • Mating begins shortly after gonopore alignment, and involves 12–24 hours of simultaneous penetration. This range was consistent across the climate's gradient.
  • Beginning at ~5 months old, a single pair mated every 4–7 days over the course of 4 months — totaling 23 sessions before this tracking ended due to the trend's stability. However, this couple became much more sedentary at ~12 months of age, which resulted in fewer encounters and prompted tracking to resume at ~13 months of age. They were then found to be mating every 6–12 days over the course of 2 months — totaling 7 sessions.
  • No signs of apophallation were ever found, as all observed matings involved two penises.
  • Eggs may be laid at as young as 8 months old, and take ~6 weeks to hatch.
  • The largest brood was 65 and a result of self-fertilization, with only one individual falling noticeably behind the others' growth.

Spot Morphology

  • Only the Button's Banana Slug and the closely related Pacific Banana Slug (A. columbianus) are known to occasionally have spots, which is determined by their alleles.
  • With very rare exceptions, spotted adults feature a single spot on their mantle, which completes its development within the egg by ~1 month. This feature is often so defined that it can even be seen through the eggshell when the fetus is suitably oriented. The mantle spot predicts whether an individual will exhibit tail spots, as it's not otherwise apparent when they first hatch. This is because all exhibit small tail speckles until ~3 weeks of age, at which point they begin to either fade away or become more defined as spots.
  • Mantle spots are situated directly above their internal shell, which is visible through the mantle until their skin turns opaque at ~2.5 months of age. The spot's location suggests that it may be a byproduct of shell development, which greatly depends upon the tyrosinase enzyme, and is coincidentially the primary driver of melanin production. Shell production is in overdrive during the early stages of development, which would explain why a spot here forms so much earlier than those on the tail.
  • Even when self-fertilized, the final presence and composition of tail spots can vary wildly within a given brood.

Additional media is available upon request.

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Successful Care

Captive Banana Slug

Meet Lil' Shrimp — my first Banana Slug. I adopted him at about an inch long, and over the course of 14 months watched him grow into a giant 12" (30cm) slug. It's thanks to him and his babies that I'd first learned much of the following.

Diet

Acceptance Sources Used
Leafy Greens Daily Dandelion, Hawksbeard, Sow Thistle, Clover Sprouts
Pollen Semiweekly Bee Pollen, Dandelion Flowers
Carrot Semiweekly Dried Carrot
Apple Semiweekly Dried Apple
Oats Semiweekly Rolled Oats
Minnow Weekly Freeze-Dried Minnow

Staple foods — containing vital nutrients.

Hydrate dry goods to avoid harmful expansion in the gut.

Climate

Temperature

  • The substrate's surface features a constant range of 55–65°F (13–18°C) by means of a height gradient and custom substrate cooler, while the enclosure's lid is ambient (~72°F or ~22°C in my case).

Hydration

  • The enclosure is fogged for 15 minutes every 12 hours, which maintains a moist substrate and vertical RH gradient of ~85% to ambient (~55% in my case).
  • Alternative success was also found with a moist substrate and directly misting each slug at least once per day. Consider ~60°F (15°C) water to minimize thermal shock.

Enclosure

Size

  • 32-Gal (120L)
  • 24"W x 18"D x 18"H (60 x 45 x 45cm)
  • Suitable for up to two adults, as they engage in courtship upon most encounters with each other, which is often stressful.

Substrate