By Nyuk Mei Liu,
Environmental Science Student, The University of Melbourne

You may have heard of iconic mutualistic relationships (where both species benefit from their interactions with each other) between coral and algae, clownfish and sea anemones, and cleaner fish and sharks. 

However, you probably haven’t heard about the relationship between tiny frogs and tarantulas. This could be because relationships between frogs and spiders vary across the globe.

In certain ecosystems, frogs feast on spiders, while in others, spiders devour frogs. It’s unlikely to find the pair co-existing harmoniously without one attacking the other.

Yet, located in a burrow somewhere in the Amazon rainforest, scientists have observed an unexpected friendship between the Dotted humming frog (Chiasmocleis ventrimaculata) and the burrowing tarantula (Xenesthis immanis).

What makes this partnership work?

Tarantulas act as a formidable bodyguard for the frogs and provide protection against predators like snakes and other spiders.¹ Adult spiders have proven to uphold their position as a vicious protector, preventing potential frog predators from entering their burrow. Researchers have found them attacking a 90 cm colubrid snake.¹

Meanwhile, the humming frogs safeguard the tarantula’s eggs by eating small invertebrates such as ants (the primary predator of spider eggs) that are attracted to the remnants of the spider’s prey – which also provide a snack for the frogs.

As such, these small amphibians have been welcomed into the tarantula’s burrows, where they live as peaceful houseguests amidst the otherwise aggressive spider family.

Seeing as they share similar lifestyles, they seem to (mostly) get out of each other’s way.

Both species remain underground during the day and forage outside the burrow at night. Adult female spiders approach and guard the entrance of the burrow at dusk, while the frogs emerge later in the evening to forage, pushing past or crawling under the towering tarantula to get out. And the tarantula doesn’t attempt to attack the frog at all as it does.

Why?

Humming frogs are friends, not food

Tarantulas are nocturnal creatures with poor eyesight, therefore relying on vibrations and chemical cues to recognise their partner frogs.

Humming frogs are approximately 2 cm in length and belong to the Microhylidae (narrow-mouthed frog) family.

While tarantulas are more than capable of preying on frogs of this size, microhylidae secrete toxins on their skin that make them unpalatable. Some juvenile spiders, upon unknowingly capturing these frogs, have been observed to inspect the humming frogs with their mouthparts before releasing them unscathed, learning not to go for them again.¹

To test whether it was really the toxins keeping the spiders at bay, researchers transferred the skin of the humming frog onto the body of a frog that tarantulas are known to prey on. Four times out of five in the trial, the spiders rejected the frog.²

During other trials, various frog species were introduced to tarantulas and found they never killed nor harmed humming frogs, though they ate the others without hesitation. They observed that humming frogs stayed motionless when held, unlike other frog species, which may have spared them from being attacked.

This indicates that tarantulas use chemosensory receptors to detect vibrational and chemical cues to differentiate their friends from food.

This unassuming alliance between tiny frogs and fierce tarantulas is only one of many unique partnerships found in nature. This seemingly odd pair embodies the remarkable bonds that can form in the wild, showcasing mutual support and cooperation despite their differences.

An alliance closer to home

We now know mutualistic symbiosis – a mutually beneficial relationship between species – is the norm for most organisms.

Symbiosis also occurs throughout Victoria’s ecosystems. Diverse lichens grow on tree trunks and rocks, providing a suitably moist environment for species of algae or cyanobacteria to grow. In return, the lichens receive some of the carbohydrates produced by photosynthesis. Plant species often live in a close relationship with fungi in the soil.

Even our gut flora represent symbiosis on a massive scale. The diversity and huge numbers of bacteria living happily in our gut that break down food, manufacture vitamins, and tweak our immune system can have a huge impact on our health and wellbeing.

Look around, and you might find symbiosis and alliances between different plant, fungi, and animal species everywhere.

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Nyuk Mei Liu is currently pursuing her Master of Environmental Science at the University of Melbourne. 

References:

1. Cocroft, R. B., & Hambler, K. (1989). Observations on a Commensal Relationship of the Microhylid Frog Chiasmocleis ventrimaculata and the Burrowing Theraphosid Spider Xenesthis immanis in Southeastern Peru. Biotropica, 21(1), 2. DOI: 10.2307/2388434
   
2. Csakany, J. J. (2003). Some aspects of the relationship between the Peruvian microhylid frog, Chiasmocleis ventimaculata, and a theraphosid spider, Pamphobetus sp. [Master’s thesis, State University of New York College of Environmental Science and Forestry. ProQuest Dissertations & Theses. https://www.proquest.com/openview/e433455b9d0fd3d9f4fe135874ef63a5/1?pq-origsite=gscholar&cbl=18750&diss=y