Nooks and Crannies
I find delving into the nooks and crannies of trees an irresistible curiosity. That’s probably because, over the years, I’ve found all kinds of unexpected and very specialised beasts lurking in the gloom, many to my great surprise.
Tree holes and cavities come in many shapes and sizes, from totally hollow or fissured trees to the gaps in or behind peeling bark. The creation of cavities is not simple process and often takes many years to form. Most are initially the result in some form of mechanical or natural damage such as lightning strikes, gale force winds, animal behaviour or human activity.
After the bark is damaged, the underlying wood is open to attack and destruction by fungi. This is often aided by insects, especially beetle larvae that spread the fungus as they bore into the timber. As the structure of the wood is broken down the damaged area is enlarged and rot-hole cavities are formed.
Some of these holes are in sheltered areas and remain dry while others, if exposed to driving rain, may remain damp or even collect and hold water. This provides a wide range of niches for wildlife.
Let’s explore the wet holes first. These tiny aquaria contain vast numbers of very specialised animals, ranging from the microscopic, slipper-shaped Paramecium and the asteroid-shaped Cyclops (remember them from your old school biology lessons?) to the three different mosquitoes which breed exclusively in such places.
Certain hover and drone flies also have their larval stage in these inhospitable stagnant pools containing rotting leaves. They overcome the lack of oxygen in the water by breathing air through a snorkel-like tube which connects them to the surface. These so-called “rat-tailed maggots” do very well in these watery crannies because of the abundant plant food, and the fact that would-be predators like beetles and dragonfly larvae do not use this habitat.
Even in times of drought these pools rarely dry out altogether, and as long as the decaying leaf mould is damp these animals’ eggs can survive, lying dormant until spring.
Permanently moist holes contain another group of creatures – including many slugs or snails – that need this environment to prevent them from becoming desiccated during the day. Woodlice are also found and are very vulnerable to dehydration: to maintain body fluid levels they can take in water by drawing it up through their rear ends!
Dry holes will provide a very important opportunity for other animals and birds. More than 20 species of British bird prefer to next in tree holes or cavities, including the blue tit, little owl, starling, kestrel and nuthatch.