Rubber Ducky Isopods (Cubaris sp.)

Rubber Ducky Isopods (Cubaris sp. 'Rubber Ducky') are the most iconic and sought-after isopods in the hobby. Discovered in 2017 in the limestone caves of Thailand, these charming creatures took the isopod world by storm and essentially created the "designer isopod" category. Their adorable yellow faces genuinely resemble tiny rubber ducks - a resemblance that sparked global fascination and transformed isopod keeping from a niche interest into a mainstream hobby.

Native to dark, humid cave environments rich in calcium, Rubber Duckies have specific care requirements that set them apart from common isopod species. They reward patient, consistent care rather than constant tinkering, and while they're more challenging than beginner species, they're entirely manageable for dedicated keepers willing to meet their needs.

These are the isopods that started it all. While many beautiful Cubaris species have since been discovered - Panda Kings, Amber Duckies, Lemon Blues - the original Rubber Ducky remains the gold standard and continues to captivate keepers worldwide.

A Glimpse

Origin: Thailand (limestone caves)

Scientific Name: Cubaris sp. 'Rubber Ducky'

Difficulty Level: Medium to Advanced

Size: Up to 1.5-2cm

Lifespan: 3-5 years

Temperature: 22-28°C (24-27°C optimal)

Humidity: 70-85%

Rarity: High (still sought-after despite increased availability)

An Overview

The Rubber Ducky Isopod's discovery in Thailand's limestone caves in 2017 marked a turning point for the isopod hobby. Before then, isopod keeping was largely focused on common species used as bioactive cleanup crews. The Rubber Ducky changed everything - here was an isopod so visually appealing, with such obvious personality, that people wanted to keep them purely as pets.

Their name comes from their unmistakable appearance. When viewed from the front, their faces feature a bright yellow "beak" that genuinely resembles a rubber duck toy. Their bodies display attractive yellow and brown colouration with distinct painted tail sections. Each isopod varies slightly in pattern intensity and colour distribution.

Taxonomically, Rubber Duckies remain formally undescribed - they're known only by their trade name and designated as Cubaris sp. (species undetermined). This is common in the hobby, where many stunning isopods from Southeast Asia await scientific description.

Understanding their natural habitat is key to successful care. They originate from dark limestone caves with extremely high humidity, stable warm temperatures, and calcium-rich substrates. Replicating these conditions - particularly the high calcium availability and consistent moisture - is essential for their health and breeding success.

While challenging compared to beginner species, Rubber Duckies are manageable for keepers who research their needs and maintain consistent conditions. They're slower-growing and slower-breeding than many species, requiring patience, but established colonies can breed year-round and produce 2-10 offspring per brood (with advanced keepers reporting broods of 10-20+).

Colour Variants

Several colour variants and related morphs exist within the Rubber Ducky lineage:

Original/OG Rubber Ducky - The classic yellow-faced variety with brown body colouration.

Blonde Rubber Ducky - Features lighter, more blonde-yellow face colouration that holds true through breeding.

Pak Chong - A related variety with bold pink face colouration instead of yellow.

Red Pak Chong - Displays red face colouration with slight red tones throughout the exoskeleton.

If maintaining pure lineages matters to you, keep different varieties separate to avoid mixing genetics.

Basic Care

Rubber Ducky Isopods require more attention to environmental conditions than common species, but their needs are straightforward once understood. The key is consistency - they thrive with stable conditions rather than frequent adjustments.

Temperature should be maintained between 22-28°C, with 24-27°C (75-80°F) being optimal. Consistent warmth encourages activity and breeding. Avoid temperature fluctuations.

Humidity is critical - aim for 70-85%. Their native limestone caves are extremely humid, and they cannot tolerate dry conditions. However, the enclosure should be moist, not waterlogged. Create a humidity gradient with approximately two-thirds kept damp and one-third drier, allowing them to self-regulate.

Ventilation is important despite the high humidity requirement. Stagnant air promotes mould and fungal issues. Provide moderate ventilation - enough for air exchange without rapidly dropping humidity. Small ventilation holes with some covered (to retain moisture) work well.

Substrate depth should be generous - at least 15cm (6 inches) is recommended. Rubber Duckies are enthusiastic burrowers and spend significant time deep in the substrate, particularly before and after moulting. Deep substrate also helps maintain stable humidity and temperature.

pH sensitivity - Rubber Duckies are reportedly sensitive to high acidity. Incorporating limestone into your substrate helps buffer pH and mimics their native cave environment.

They're shy and secretive by nature. Once disturbed, they often conglobate (roll into a ball) and may remain that way for extended periods. Minimise disturbance - they do better when left largely alone to establish their own routines.

Feeding

Rubber Ducky Isopods are detritivores requiring a varied, nutrient-rich diet with particular emphasis on calcium and protein.

Primary foods (should always be available):

Hardwood leaf litter (oak, magnolia - pesticide-free is essential)

Rotting white wood pieces

Sphagnum moss and forest moss

Lichens

Supplementary foods (offered 1-2 times weekly):

Fresh vegetables - cucumbers, sweet potatoes, carrots, courgette

Protein sources - dried shrimp, fish flakes, dried minnows, crickets

Commercial isopod foods

Calcium supplementation is absolutely essential for this species. Their native limestone caves provided abundant calcium carbonate, which they use to build their exoskeletons. Colonies thrive when calcium is readily available. Provide multiple calcium sources:

Limestone pieces or powder (mimics natural habitat - highly recommended)

Cuttlefish bone

Crushed eggshells

Crushed oyster shell

Crushed coral

Some keepers report that while colonies survive with just cuttlebone, they truly thrive when limestone is the primary calcium source.

Protein is important for breeding success. Offer protein sources twice weekly - dried shrimp, fish flakes, or small dried insects work well.

Feed small portions and remove uneaten fresh food promptly to prevent mould. These isopods eat less than larger species, so adjust quantities accordingly.

Appearance and Behaviour

The Rubber Ducky's appearance is what made them famous. Their faces feature a distinctive bright yellow "beak" and facial structure that genuinely resembles a miniature rubber duck toy. When viewed front-on, the resemblance is uncanny and utterly charming.

Their bodies display yellow and brown colouration arranged in attractive patterns. The yellow upper body contrasts with darker brown patches, and their tails show distinct painted markings. Colouration varies between individuals, with some showing more intense yellow and others displaying deeper brown tones.

Adults reach approximately 1.5-2cm in length. Their bodies are divided into seven segments, each with a pair of legs. Two legs are specialised for burrowing, allowing them to dig deep into substrate - up to six inches.

Like all Cubaris, they have a hard exoskeleton that provides protection and requires regular moulting for growth. Calcium availability is crucial for healthy exoskeleton development.

Two antennae on their heads serve as primary sensory organs, helping with navigation, chemical detection, and communication. Small projections called cerci on the antennae function as additional sensory organs.

Behaviourally, Rubber Duckies are shy and secretive. They're primarily nocturnal, doing most foraging at night, though established colonies may venture out during the day. When disturbed, they readily conglobate into a tight ball and may remain rolled up for extended periods.

They're non-aggressive and have calm temperaments. While initially wary, comfortable isopods can become surprisingly interactive - some keepers report their Rubber Duckies will sit in their hands for several minutes once trust is established.

They don't typically attempt to escape when housed appropriately with sufficient food and humidity.

Habitat

Creating the right habitat is essential for Rubber Ducky success. Their natural limestone cave environment provides the template.

Enclosure options:

Plastic containers with ventilation - ideal for breeding colonies due to easy humidity control

Glass terrariums - attractive for display but require careful ventilation management

Minimum 10 gallons for 10-15 isopods, though they don't require large spaces

Temperature: Maintain 22-28°C consistently. Warmth encourages activity and breeding.

Humidity: 70-85%, with a gradient (approximately two-thirds damp, one-third drier). Mist with dechlorinated water as needed.

Ventilation: Moderate - enough for air exchange without excessive humidity loss.

Substrate depth: At least 15cm (6 inches) to allow deep burrowing. This is important for their moulting process and overall comfort.

Lighting: Low or indirect. As cave-dwellers, they don't require bright light. Terrarium lighting can be used but shouldn't shine directly on the isopods.

Water parameters: If maintaining standing water (e.g., for misting), pH should be 8.0-8.5 and hardness 10-15° DH.

Hiding spots: Provide bark, cork, leaf litter, and moss. These shy isopods need secure retreats.

Consider bioactive setups with live plants and springtails to create self-sustaining ecosystems. Springtails help control mould and maintain substrate health.

Substrate Mix

The substrate is crucial for Rubber Ducky Isopods - it provides food, maintains humidity, allows burrowing, and must supply adequate calcium to mimic their limestone cave habitat.

Essential components:

Decomposing wood mulch

Sphagnum peat moss

Coconut coir (for moisture retention)

Limestone pieces or garden lime (calcium carbonate - essential)

Rotting cork bark

Natural leaf litter (pesticide-free oak, magnolia)

Charcoal (helps with drainage and pH)

Recommended ABG-style mix:

Sphagnum moss - 1 part

Tree fern fibre - 2 parts

Orchid bark - 2 parts

Peat moss - 1 part

Charcoal - 1 part

Add to the mix:

Limestone powder/pieces throughout

Crushed eggshells or cuttlebone

Rotting white wood

Generous leaf litter layer on top

The limestone is particularly important. Rubber Duckies originate from calcium-rich limestone caves, and incorporating this mineral into the substrate has proven highly successful for many keepers. Garden lime (calcium carbonate) is an affordable, readily available option.

Create depth of at least 15cm. Layer sphagnum moss over approximately one-third of the surface to create a humidity gradient.

Some advanced keepers add red wiggler composting worms to increase microbial diversity in the substrate, with reported improvements in colony health and breeding success.

Breeding

Rubber Ducky Isopods are slower breeders than many species, but they reproduce reliably once established and comfortable.

Acclimation period: New colonies typically need several months to fully acclimate before breeding begins. This can be a "painfully slow process" - patience is essential. Some keepers report waiting 6-7 months before seeing their first babies.

Breeding age: Female Rubber Duckies can begin breeding at approximately three months old.

Breeding frequency: Once established, they breed year-round with consistent conditions.

Brood size: Typically 2-10 offspring per brood. Advanced keepers with optimised conditions report larger broods of 10-20+.

Lifespan: 3-5 years with proper care, providing multiple breeding opportunities.

For breeding success, maintain stable conditions with high humidity (70-85%), temperatures at 24-27°C, deep substrate for burrowing, abundant limestone/calcium, regular protein supplementation, and minimal disturbance.

Females carry eggs in a brood pouch (marsupium) until hatching. The tiny mancae can be raised alongside adults.

Rubber Duckies spend significant time fully submerged in the substrate before and after moulting. This burrowing behaviour is connected to breeding - deep substrate allows them to create secure chambers for reproduction.

Don't be discouraged by slow initial progress. Once conditions are optimised and the colony establishes, breeding becomes more consistent.