One of the more common enquiries we receive is “What animal made this hole in my garden?”. Unfortunately, holes are some of the more difficult things to identify, as a photo usually doesn’t contain that much information.
Animals sometimes create holes (a hollow spot in the ground) or burrows (shelter made in the ground often used for habitation). Animals can also make holes while foraging for food, especially in the case of bandicoots.
We have tried to include the most common holes/burrows that can be found in the Greater Sydney area, so some animals further out of this area might not be included in this post.
When identifying holes, we try and see if there are any clues in the images and make an educated suggestion based off what information we can see or that the enquirer has provided.
Some of the questions we need to ask to narrow down the hole occupant include: where is the hole (is it next to a tree, under cover, out in the open), are there any special features (soil on the side, silk lines radiating out from the hole, a cap on the burrow) and how large is the hole. We would also need to know where the structure was found (in a garden, near a national park and where in Australia it was found). Holes that are found in a suburban environment can be different to the ones we find in the bush. For example, spider burrows out in the bush can have unusual looking trapdoors, palisades and tubes leading up rocks. Smallish burrows that are found in a swamp could indicate the burrow of a crayfish.
Soil composition is another tool that can be used to help us identify what type of animal created the hole. A small hole in sandy soil could mean the home of a Sand Wasp. Holes found in clay soils could indicate the presence of Blue Banded Bees.
Of course, this is not a fool-proof method. Often it is best if we see an image of the animal inside the hole so we can confirm if the hole is indeed from that particular animal.
In summer, small holes next to trees are excellent indicators of cicadas and help us understand the cicada life cycle. Female cicadas use their ovipositor (a tube-like structure at the end of the body of female cicadas and other insects used to lay eggs) to make slits on branches, where she will eventually lay her eggs. The nymphs then hatch and drop down, burrowing into the soil to feed upon the sap from tree roots. Just before it emerges from the ground, the cicada will create a turret of soil that stops water and mud from entering the hole. Then, after a bit of rain, the juvenile cicadas emerge from the soil, leaving behind a clean hole. Seeing the shedding (also called the exuvia) on a nearby tree or post will add a little more evidence to the observation.
Burrows that have silk lines radiating outwards and are under cover, or in a shady part of the garden, tell us that it could be the home of a Funnel Web Spider. The silken strands around the burrow work as trip lines, used to alert the spider hiding inside the burrow that something is outside.
Trapdoor Spider burrows are frequently confused with those of a Funnel Web. However, Trapdoor Spider burrows can have a ‘lid’ or be completely open with a ‘collar’ of silk around the entrance. The burrows of the Trapdoor Spider are more likely to be out in the open when compared to the secluded and covered burrows of Funnel Webs.
Small holes, around 2-3cm in diameter, could indicate Wolf Spiders. Their burrows can have completely open holes with no silk, and some use a trapdoor to close the burrow. In wetter weather, Wolf Spiders in arid areas construct turrets to stop water from entering.
The hole in your garden could also be from an earthworm. Earthworms aerate the soil, which means they spread the soil out and decompress it, allowing air (oxygen) to travel below the soil. This normally goes unnoticed as it happens underground. However, if the soil is compressed and saturated with water, the oxygen that earthworms need to breathe cannot pass through the soil to the areas deeper down where they burrow. To help oxygen to flow deeper, the worms make holes at the surface. If the surrounding area is compressed, the soil that passes through the gut of the earthworm and out the other end has nowhere else to go but out the hole the worm has made, resulting in dark mounds. These are called ‘worm casts’.
Larval beetles can also emerge from the soil, leaving behind a hole. Many avid gardeners would have noticed small, white grubs in the garden while digging through the soil. These white larvae (also known as curl grubs), if allowed to complete their lifecycle, go from a pupa (the next life stage that is in between the grub and adult form) and turn into an adult beetle.
Bees, wasps, crickets and larval butterflies and moths (caterpillars) have also been known to create holes in the garden. Ants create more complex burrows underground but, on the surface, a simple opening usually surrounded by sand or dirt is visible.
Larger holes can indicate the presence of rats, especially if the hole is located near a chicken coop or compost heap. Rats build burrows from their nest to their food source but can also use them as an escape route.
If you suspect rats are the culprits, you can check for greasy marks left on the sides of buildings. Rat holes/burrows look different when comparing them to the conical bandicoot feeding hole. Bandicoots feeding holes are around 10cm deep and have a mound of dirt lying beside the hole. Usually looking for curl grubs (larvae of scarab beetles), the bandicoot aerates the soil and assists with organic mixing of the soil.
In Sydney, the most common bandicoot species is the Long-nosed bandicoot (Perameles nasuta). Scat (poop) and footprints can help identify burrows of larger mammals. If you see some scat or footprints in the soil, that could give you some more clues as to who is living inside the burrow.
Reptiles dig by pushing soil outwards instead of between their legs. Their burrows (usually but not always) have a more triangular shaped opening. Erosion can change the shape of the opening which makes identification tricky. If claw marks or scats can be seen around the opening, it would make identification easier.
To make things a little more difficult, animals have been known to be opportunistic and use the burrows other animals have made.
In the end, holes are particularly tricky to identify and there are always exceptions to the ‘rules’, depending on the species. The best way to identify what is occupying a burrow is to see what animal is inside. If the structure doesn’t seem quite deep enough, it is probably a feeding hole, in which case, see if there are any scats or footprints nearby.
Try looking at the burrow at various times during the day, early morning and at night to see if you can spot any animal residing, entering or exiting the burrow!