Invertebrates - The Lowly Worm

Perhaps you've never spared any thought for worms aside from when you are doing some backyard gardening and inevitably find some earthworms with your shovel! But while you're looking at all the wonderful and colourful animals of the rainforest, don't forget that the smallest creatures sometimes have the most important roles. Maybe you've never thought about worms before because nobody told you anything about them. If that's the case, you've come to the right place.

There are roughly half a dozen categories of worms and quite a few of these are marine species. Three classes of worms we would expect to find in the rainforest are flatworms, nematodes (roundworms) and annelids (segmented worms and leeches).

Some of these are notoriously parasitic (such as those which live their lives in something's intestinal tract!) while others are involved in the important job of breaking down decomposing material in the soil, thereby releasing nutrients for use by living things.

 
Flatworms

Tropical gardeners know these as the colourful but slimy worms that are found under rotting wood or vegetation in the compost bin. They have a coating of mucous to prevent their bodies from drying out. This mucous layer also helps their movement as they put down the slimy layer and use tiny cilia feet to slide forward over it. Flatworms are carnivorous and feed on slugs and earthworms. They are hermaphroditic (have both male and female organs in the one body) but some species can also 'duplicate' themselves if they were split in half! A well known flatworm of school days is the Planaria - a little flatworm with a shovel-shaped head. A school experiment of long ago was the old 'two headed trick': if this worm were to be cut through the middle of its head, it would regenerate each of the missing halves and therefore, end up with two heads!

Nematodes (roundworms)

There are thousands of species of these but the vast majority are either microscopic or only 1mm (about 1/32nd of an inch). Not all are parasitic but those that are make quite an impression on us, our pets, wildlife and even the agricultural industry. Some nematodes are actually used to control other pests and research is progressing in this area. If you would like to know more about nematodes, check the websites of major universities. One is listed here to get you started: the Nematode Collection at Adelaide University

 
Annelids (segmented worms and leeches)

In the Wet Tropics region, researchers have already found and described roughly 40 species of earthworms (not including introduced species) out of a total of 325 earthworm species known throughout Australia. Researchers believe, however, that there are hundreds more species waiting to be found. Some of the species described thus far from the Wet Tropics area have been found in only one location but others are common throughout the area.

One of Australia's leading earthworm experts, Dr. Geoff Dyne, offers the following about the role of earthworms in the rainforest: "Earthworms are very important in the economy of the forest, as major translocators of rotting materials and in the recycling of nutrients. They physically break down rotting wood on the forest floor and churn and aerate the soil, incorporating leaf litter into the upper soil layers - thus, encouraging their decomposition by bacteria and fungi. Some species are capable of digesting cellulose. "In the forest, they can often be seen under rotting logs, rocks, or in other moist microhabitats (particularly when there has not been recent rain). People should replace logs, etc as the earthworms and other sensitive creatures sheltering can dessicate and die if exposed for any time."

There are also some earthworms in the Wet Tropics which excrete a fluid which is bioluminescent (gives off light) and eerie greenish trails have been seen during the wet season where the earthworms have travelled after being forced from their flooded burrows.

Leeches are another of the segmented worms but, unlike earthworms which are hidden from view in the soil, no effort is required to find leeches - they are very good at finding you. Not all leeches are interested in warm blooded animals with some being more interested in sucking the juices out of snails and other worms. When their preferred prey is not found, leeches will feast on other choices such as fish, frogs, turtles or birds.

Leeches are sensitive to changes in light and other stimuli and they stand erect and wave their body around to pick up the sensations from an animal. Then they use the inchworm crawling technique to head for their target. If you'd like to observe this first hand, sit down on the rainforest floor and then watch the ground around you closely. Leeches also find their food by accident, say when a bushwalker brushes past.

Leech bites are annoying but it is believed that they do not transmit any diseases so they really aren't as bad as other biting pests. They feed by sucking blood or body fluids from their host and this is made easier by the anti-coagulant they squirt into the wound. Their saliva also has a numbing agent to desensitise the victim's skin so that the bite isn't noticed. This is why the leech is normally not discovered until it has finished its meal and the trickle of thinned blood from the wound is noticed. Some people seem to be allergic to leech bites and experience a delayed itching followed by a scar which takes many months to fade away.

Want to learn more about leeches? The Australian Museum in Sydney has a fact sheet on the little suckers.

 
Worm profile

Some of the largest earthworms in the world are found in the Wet Tropics. One in particular (Terriswalkerius terrareginae) is a deep blue colour and is reported to grow up to two metres (6 ½ feet) long! It has been found at various high altitude locations in the Wet Tropics including Mt Lewis and Mt Bellenden Ker. This large worm forms deep burrows but sometimes, after very heavy and prolonged rains, the big worms are forced from their flooded burrows and can be more readily seen moving on the forest floor (and roads and tracks) during the day.