- Geckos are lizards with many unique adaptations.
- House geckos are commensals and have enjoyed the association with humans for thousands of years.
- Reptile parks and zoos should create more awareness about the role of geckos.
- The views in the commentary are that of the author.
Geckos are some of the most fascinating creatures in the animal kingdom. Geckos are lizards, yet not all lizards are geckos. With tails that can be detached and regrown at their will, a flat and flexible tongue that can clean their own eyes, geckos have evolved to thrive in different habitats. They do not have hard scales covering their soft skins. Their eggs however are hard-shelled and round. Many gecko species are even capable of vocalisation.
With some exceptions, these generally nocturnal creatures can scale smooth surfaces including glass and even walk upside down defying gravity, earning them the nickname ‘wall lizards’. There are also diurnal gecko species, such as the Andaman emerald gecko (of the genus Phelsuma) and the highly diverse forest-dwelling dwarf geckos (of the genus Cnemaspis).
Diversity and adaptations
More than 100 species of geckos are known in India which may be around 20% of the country’s reptilian species diversity. India’s geckos are placed under two families: Eublepharidae, which includes the few species of ornate geckos popularly called leopard geckos; and Gekkonidae. Geckos in India vary considerably in size. Adults of the forest-dwelling dwarf geckos hardly exceed the length of a finger whereas, giants such as the tokay gecko can be as long as the forearm.
Four species of geckos widely inhabit homes and other human dwellings in India. These are the northern house gecko, bark gecko, Brook’s gecko and the waif gecko. With some practice, the four species can be identified without difficulty, including their calls.
Many other species may locally invade homes and gardens as the emerald gecko in the Andaman Islands, and the tokay gecko in the northeastern Indian states and in cities like Bengaluru.
Geckos primarily eat insects. However, larger species can eat small vertebrates including their own kind. Species that have become commensals, have adapted to eating other kinds of provisioned food such as cooked rice and crumbs of bread that fall on the floors. They like fruits and sweet juices and would not hesitate to lap up tea or coffee spilt on floors and dining tables. This behaviour is known even in the otherwise shy Andaman emerald gecko.
Larger-sized bark geckos that are common inside houses in Chennai, are known to bite holes in chicken eggs and feed on the contents that oozed out. They even enter bins in the kitchen and pick up small bones and glean them.
Light, warmth and hitch-hiking
Like all reptiles, geckos are cold-blooded and need to bask under the sun to metabolise. However, basking in the open comes with the risk of predation. When the luxury of warmth and safety were together offered for free by cave-dwelling humans, it became conducive for a few species of geckos to become commensals of humans locally. Bonfires lit by cavemen attracted insects during nights that the geckos fed on. The human-gecko bond thus grew and has since persisted.
Modern homes with heat generating electric devices, such as lights, televisions and cooking stoves and scores of household insects, have provided the most hospitable habitats to the adaptive geckos. House geckos have thus become a part of human habitations worldwide.
Geckos have also travelled far and wide aided by people. Earliest examples of hitch-hiking by geckos may be traced to species like the endemic Andaman emerald gecko. That its geographical distribution overlaps with that of the primitive Negritos of the islands supports this assumption. Curiously, it is absent in the Nicobar Islands. This species has all its close relatives in East Africa and Madagascar.
Hitch-hiking by geckos is known in more recent times as well. The Porbandar gecko (Hemidactylus), discovered from the well-known port in Gujarat may just be one example. Ships may have also carried other species of geckos into India. This is not uncommon in reptiles as around twenty years ago, a young cat snake (Boiga) arrived in Chennai along with timber shipped from Africa. The snake was rescued by personnel of the forest department and brought to the Chennai Snake Park. The four-clawed or Pacific gecko (Gehyra), which is a native of the Indo-Pacific region, including the Nicobar Islands, can now be seen locally inside houses in Kerala. There can be many other species of geckos hitch-hiking without being noticed.
One gravid female gecko is enough to found a new population. A female slender gecko (Hemiphyllodactylus) caught in Bengaluru, for instance, survived in Chennai and laid eggs. The eggs hatched. Eggs that get transported by humans inadvertently help geckos colonise localities far and wide. Further, some species of geckos are parthenogenetic so that a single female is enough to found a new population wherever conditions are favourable.
The role of geckos
Geckos that dwell with humans play important roles in keeping homes free of insects. However, they have the tendency to rest in one nook and can dirty the space with their foul-smelling excreta. Many house-keepers do not tolerate this. Female bark geckos tend to attract males during the breeding season resulting in a sudden inflow of large geckos. Eggs are laid inside bookshelves, cupboards, vases and any space left unused for a while. The sight of baby geckos running about the floors is resented by some. Other than these inconveniences, geckos are totally harmless.
They are neither venomous nor is their flesh poisonous as many believe and fear. Reports of food-poisoning due to a gecko that fell into drinking water or food are mostly made up to avoid punishment. When people had no piped water supply at home precious water had to be drawn from a well or collected from other sources each day for domestic needs. Traditional houses had plenty of geckos and it was not uncommon for one or two to fall into the stored water left open during nights. They were often discovered only in the mornings after they had spent several hours swimming and attempting to stay afloat. People used to remove the geckos and continue using the water.
Geckos are consumed by many species of birds including domestic chicken. Cats and dogs that pick geckos in their mouths feel no discomfort. On the contrary, if a cat or dog by mistake took a toad (Bufonidae) in its mouth it will immediately throw it out and profusely drool or salivate. This is because toads have parotoid glands that secrete mild toxins. Prolonged handling of toads can cause irritation of the skin and eyes in people. Adult toads, therefore, have few predators. But all geckos are vulnerable to predation.
Many species of geckos are even popular as pets in different parts of the world. There have been no reports of geckos causing allergies or serving as carriers of infectious diseases. Geckos have dry skins and they shed their skins periodically.
The toes of house geckos can potentially carry microorganisms along with dirt between the tiny folds. However, there is no scientific evidence to support this presumption. There were also speculations that geckos may carry dangerous bacteria such as Salmonella, an agent of food poisoning. This is however unlikely, since Salmonella like most other bacteria are killed when food is well-cooked. In a rare event that Salmonella was indeed carried by a gecko, and the food got contaminated by it, it would happen only if the cooked food was already cold.
Geckos are gentle creatures. Even the larger individuals do not bite unless carelessly handled. When left alone, they just mind their own business. They have adapted to the harshest forms of urbanisation making them indomitable. Reptile parks and zoos should therefore do more to educate people about geckos. They are the only reptiles that have become true commensals of humans.
Read more: [Commentary] Tracing the leopard gecko’s story from pet trade to lab and beyond
CITATIONS:
Daniels, R.J.R. (1996). The Vanishing aborigines of the Andaman and Nicobar Islands. Current Science 70:775-776.
Daniels, R.J.R. (2001). Amphibians and reptiles of Madagascar and the Mascarene, Seychelles and Comoro Islands (Book Review). Current Science 80(2):299-300.
Daniels, R.J.R. (1994). Notes on a rare South Indian gecko Hemiphyllodactylus typus Beddome. Dactylus (USA).
R.J. Ranjit Daniels is an ecologist with the Care Earth Trust, a Chennai-based biodiversity and conservation organisation.
Banner image: A Prashad’s gecko spotted in Amboli, Sindhudurg, Maharashtra. More than 100 species of geckos are known in India, comprising as much as 20% of the country’s reptilian species diversity. They belong to two families: Eublepharidae and Gekkonidae. Image by Ninad Bhosale via Wikimedia Commons (CC BY-SA 2.0).
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