Hidden housemates: a gecko invasion?

In northern Australia some houses are filled nightly with chatter. You might hear a distinctive “chuck-chuck-chuck”, or find calling cards (droppings) on skirting boards, picture frames and window sills. If so, you probably have gecko housemates.

If you live anywhere from Brisbane to Broome, it is likely your house is home to two very similar species, the introduced Asian House Gecko (Hemidactylus frenatus) and one of several species of native Australian counterparts, the dtellas (Gehyra sp.).

Other native species you might see around your house include the velvet geckos (Oedura sp), while other introduced species include the Mourning Gecko (Lepidodactylus lugubris).

As nocturnal reptiles, geckos generally hide during the day and emerge at night. The species we see around our homes are taking advantage of the insect-attracting lights that fill our cities and towns. These provide an endless smorgasbord of food for the geckos.

Asian House Geckos established themselves in Darwin in the 1960s. It is most likely they travelled here as stowaways in cargo ships. Since then their distribution has expanded along transport routes. They are now found along the northern and eastern coasts, most commonly around buildings or other manmade structures.

Who are your gecko housemates?

Check a reptile field guide to see which geckos are in your area. Most of them can be identified fairly easily, but if you live with Asian House Geckos (Hemidactylus frenatus) and dtellas (species of Gehyra) you will need to pay extra attention.

The following tips will help you tell your Hemidactylus from your Gehyra:

• Looks: Both species are similar in size, about 11 cm total body length, and are pinkish-brown to dark grey with velvety skin and large eyes. If you look closely, the Asian House Geckos have spines on either side of their tail. Each of their toes has claws. Dtellas, on the other hand, are spineless. They have claws on their outer toes but the toe closest to their body is clawless.

The Asian House Gecko arrived in Australia in the ‘60s. If you look closely, you can see spines running down its tail. magdalena_b/Flickr

• Call: Asian House Geckos are much louder and more talkative than natives; their “chuk-chuk-chuk” is sometimes described as “scolding”, whereas native geckos tend to chatter very softly.

• Eggs: Both Asian House Geckos and native geckos lay one or two eggs that are round, hard-shelled and resistant to moisture loss.

Who rules the house?

An intrepid gecko’s eggs laid in a keyhole. Charlie Allom/Flickr, CC BY-NC-ND

Are introduced geckos pushing out our native species? While they have been implicated in the exclusion of native house geckos, the extent of this is unknown.

One theory is that the hunting style of the Asian House Gecko gives them an advantage under bright city lights. These geckos are active hunters and can feed efficiently where insects congregate around artificial light. Native geckos, on the other hand, seem to forage where prey is more dispersed.

Indeed, Asian House Geckos are willing to use more brightly lit areas, whereas natives choose darker areas.

While Asian House Geckos may have access to more insects in light areas, it’s possible that some native species and the house gecko are exploiting different parts of the “house gecko niche” and happily living together.

Geckos in the bush

Asian House Geckos have been recorded in natural habitats away from our homes. Could they invade native bushland?

On various islands of the Pacific and Indian oceans, introduced Asian House Geckos displace resident geckos from the house-gecko niche and have managed to spread beyond areas of human habitation. Most notably, in the Mascarene Islands, Asian House Geckos have invaded all natural habitats. This has led to the decline of the native Nactus gecko populations and the extinction of three species.

But perhaps this is not the case in Australia. Surveys conducted across northern Australia failed to find evidence that Asian House Geckos were successfully invading natural habitats. Based on this study, it seems this species will continue to thrive with people but is unlikely to spread further. More research is underway to investigate if Asian House Geckos are invading the bush in different parts of their range.

Scientists agree, however, that novel parasites and pathogens carried by Asian House Geckos could pose a threat to Australian wildlife. We don’t know, but it’s definitely something to watch.

Next time you come across your gecko housemates, take a closer look. Are you harbouring native species, or a potential invader?