THE KEEPER OR THE KEPT?

The story behind tarantulas with pet frogs.

Every now and again a bizarre scientific story captures the attention of the masses. In some cases, these stories seemingly resurface every few years for a bewildered generation. Usually, these waves of intrigue are spurred on by social media trends and the latest story to go viral on TikTok is that of giant tarantulas keeping “pet” frogs. Symbiotic relationships are common in the animal kingdom and therefore, this anthropomorphic tale of two unlikely friends seems reasonably plausible. Is this a far-fetched Pixar-esque an anthropomorphic pipe dream, or is there some science behind the story?

The frog and the spider

The “pet frogs” that are frequently seen in close proximity to tarantulas are generally from a specific group of amphibians called “Microhylidae”. Microhylid frogs are commonly known as “narrow-mouthed frogs.” There are 683 species of these frogs found all over the world. Some are beautifully patterned and grow up to 10cm long while others are barely visible creatures, never exceeding 10mm in length. Some species are frequently kept in captivity such as the very charismatic “chubby” frog (Kaloula pulchra). Most Microhylids are very small, terrestrial frogs that occupy leaf litter in tropical and subtropical forests, although it is almost impossible to summarise the family. Some thrive in arid landscapes, burrowing beneath the soil for large parts of the year whilst others are arboreal with toe pads and breed in tree trunk holes in the forest canopy.

Just as the “pet frogs” are from a very diverse group of animals, so are the tarantulas. Theraphosidae contains around 900 different species of tarantula and they can be found across most warm climates. Although most records of spiders with “pet” frogs focuses on one genus of South American tarantula, the family is extremely broad and convergent evolution is reasonably common, indicating this phenomenon may not be restricted to a particular species or genus.

Symbiosis

The first published observation of a “spider keeping a pet frog” dates back to 1989. Whilst studying entomology in Peru, Reginald Crocraft and Kieth Hambler observed a “close association” between a Microhylid frog (Chiasmocleis ventrimaculata) and a Colombian lesser back spider (Xenesthis immanis). They claimed that the spider seemed to allow the frog to share its burrow, despite being perfectly capable of killing and feeding on the frog. They even observed the spider seemingly moving its legs to allow the tiny amphibian to pass in and out of the burrow. Both species are nocturnal and when the spider would emerge from its hole to hunt, the frog would follow.

Initially, it was thought that the spider was simply ignoring the frog. Since Crocraft and Hambler’s discovery, others have observed young spiders picking up the tiny frogs, examining them with their mouthparts and putting them back down again, suggesting that the frogs may have some form of chemical defence. The frog benefits from the protection of the spider, while the spider must tolerate its new tenant. This form of relationship is called commensalism, where one organism benefits from the other one but neither is harmed. However, further studies suggest that there may be further benefits for the unlikely duo.

It appears that the spiders choose not to eat the frogs as they also offer protection for the spiders’ eggs. The frogs will prey on tiny insects that are too small for the tarantula to fend off. These little bugs (including ants, mites, etc) are attracted by the leftovers of the spiders’ much larger prey but would undoubtedly enter the spiders’ burrow to feed on its egg sac and newly hatched offspring. Because it seems that both species are benefitting from the symbiotic relationship, it is described as mutualism. Across the animal kingdom, inter-species mutualistic relationships are well-documented. In extreme cases, these relationships have prompted some species to become entirely reliant on another species for survival.

In 2002, Jolene Csakany suggested that Crocraft and Hambler’s original description of Xenesthis immanis may be incorrect. The “Colombian” lesser back spider’s range does not stretch as far south as Peru and so Csakany set out to find out which species actually exhibit these strange behaviours. She discovered the black spider referenced in 1989 was possibly an undescribed species of chicken spider (Pamphobeteus spp.) She tested this theory by taking the skin of a humming frog and putting it onto two different bullfrog species (Leptodactylus) (both species that the tarantula would usually prey upon) and discovered that the tarantula would not eat the animal with the humming frog’s skin. This supported the theory that the frog’s chemical compounds within its skin help the tarantula identify friends from food.

All around the world

As the story of symbiotic relationships between Arachnids and amphibians engulfed the curiosity of entomologists and herpetologists internationally, new cases are continuing to be unearthed each year. Perhaps the most startling came in 2008 from Rameshwaran Island, off the southeast coast of India. Researchers reported an “unusual” relationship between another Microhylid, the Sri-Lankan painted frog (Uperodon taprobanicus) formerly, Kaloula taprobanica and a member of the Poecilotheria genus of tarantulas. Any invertebrate

A friendly bunch

keeper will know just how popular Poecilotheria are in captivity. They include the Gooty-sapphire ornamental tarantula (P. metallica), ornate tiger tarantula (P. ornata) and the Indian ornamental tarantula (P. regalis). Poecilotheria is known for being extremely aggressive, arboreal spiders that pack reasonably potent venom. Yet, despite their unwelcoming characteristics, they have been recorded sharing a hole with the rather unassuming bullfrog.

In 2009 Poecilotheria ornata and Poecilotheria subfusca were also reported to seemingly have close relationships with the Microhylid frog Uperodon nagaoi The frogs and the tarantulas were recorded sharing tree holes, many of which contained eggs and/or juveniles of the spider, the frog or both “partner” species. The researchers found that the Poecilotheria tarantulas would actively protect the frogs’ eggs from predatory geckos ( Hemidactylus depressus ). As the eggs (and frogs) are ultimately defenceless without the spiders and the spiders’ eggs are defenceless against small insects, there is reason to believe the two species are reliant on one another.

Herpetologists and Entomologists are also startled by the fact that both cases of mutualism are enacted by species from different lineages on two entirely different continents. Other scientists have also recorded some form of association between the Tungara frog ((Engystomops pustulosus (formerly Physalaemus pustulosus)) and tarantulas of the genus Aphonopelma in Mexico. Whilst research into the topic is still developing, every observation indicates that this relationship has evolved multiple times across the world.

Colombian lesser back spider

The Colombian lesser back spider is a medium-sized tarantula from Colombia and Venezuela. They are generally black with a purple/pink starred pattern. Their striking appearance makes them reasonably popular in captivity, where they are reported to be quite skittish. Scientists have reported a close association between this species and two distinct species of Microhylid frog.

Bird spider

The “bird” or “chicken” spiders of South America are amongst the largest Arachnids in the world. There are currently 18 described species, most of which are very stocky with up to 16cm leg spans. The genus is constantly undergoing taxonomic changes and many formerly Pamphobeteus now belong to the Vitalius genus. Bird/ chicken spiders received their common name from tales of them stealing chicks from farms within the Amazon basin. Their enormous size suggests these stories may have some element of truth.

Dotted humming frog

The dotted humming frog is native to the lowland rainforests of western South America. They are around 2cm in length and inhabit dense layers of leaflitter. Little is known about their activity during dry seasons, but they will typically emerge as wet season approaches and produce up to 400 eggs in a single clutch. This species has been recorded sharing burrows with tarantulas and in some cases, multiple frogs will share the same burrow. Although the dotted humming frog will leave the burrow to hunt, they generally stay within 5cm of the burrow.

Ornate tiger spider

The ornate tiger spider is a large species of arboreal tarantula from Sri Lanka. They are an endangered species in the wild but are frequently bred in captivity. Their appeal within the trade can likely be attributed to their vibrant colouration and feisty attitudes. Ornata is the secondlargest of all Poecilotheria and can be identified by its vibrant yellow/orange patches beneath its legs.

Sri Lankan painted frog

Uperodon taprobanicus

Formerly classified under the Kaloula genus like its similarlooking counterpart the “chubby” frog, the Sri-lankan painted frog is an ornate species of fossorial amphibian from South Asia. It is a plump species that can grow up to 7cm in length and is highly adaptable. This species is found in a range of habitats from dry forests to humaninhabited areas up to 1,300m in elevation.

Sri Lankan leaf-nosed gecko

Hemidactylus depressus

The Sri Lankan leaf-nosed gecko is a small species of gecko endemic to Sri Lanka and nearby islands. They are found across the plains and close to human-inhabited areas where they occupy crevices in tree trunks, caves and occasionally, buildings.

Tungara frog

Engystomops pustulosus

The Tungara frog is a species of Leptodactylid frog from Central America and Mexico. They are a warty species that, for a long time was falsely considered a toad. Like the dotted humming frog, the Tungara frog is a terrestrial species that rarely exceeds 2cm in length and feeds on tiny insects amongst leaflitter. However, this species does not occupy burrows and males will generally congregate around temporary pools of water to call for a mate.

North American tarantulas

Aphonopelma sp.

The Aphonopelma genus is an enormous genus of tarantulas that contains almost all North American species. As of last year, the World Spider Catalogue accepted 59 species although there may be up to 87 species within the genus depending on the source. This means that Aphonopelma makes up almost 10% of the world’s tarantula species.

Are your tadpoles bloated – maybe with pink or yellow discolouration around the abdomen?