Outdoors_lol_08-42

Jeff Green | Oct 23, 2008

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Just before Halloween, it seemed appropriate to have a column on a few of the eerie, macabre things that go on in the natural world. Some of the creepiest things come from the worlds of fungi and insects – sometimes from both at the same time, as you will see.

First we’ll start with something from the plant world – a vine-like annual plant called a dodder. There are several species of dodders in our area, and a few are considered agricultural pests. After the dodder seed germinates, the plant starts out as just a tiny tendril with no roots or leaves. It then has about a week to find a host plant it can wrap itself around. The vampire-like dodder then sinks its plant-fangs into its victim and starts drinking its juices. Scientists have recently discovered that the dodder uses scent to find its victims. Its behaviour has been described as animal-like because it creeps toward the smell of a preferred host. Apparently the dodder prefers certain odours – for example given a choice of tomato or wheat, the dodder picks the tomato. It is possible that wheat gives off a chemical that repels the dodder seedlings.

The next creepy tale is from the insect world. Most people are familiar with a group of wasps known as mud daubers. They are solitary wasps that construct small nests of mud in or around homes, sheds, and barns and under open structures, bridges and similar sites. These insects are long and slender with a narrow, thread-like waist. Some are a solid steel blue or black but others may be brown with additional yellow markings.

This wasp group is named for the nests that are made from mud collected by the females. Mud is rolled into a ball, carried to the nest and moulded into a cell-like structure with the wasp's mandibles. Here is where it gets interesting. After completing the mud nest the female captures several insects or spiders to supply the cells. Prey are stung and paralyzed – but not killed – before being placed in the nest. A single egg is deposited on the prey within each cell, and the cell sealed with mud. The wasp larva that hatches from the egg feeds on the live prey items left by the adult wasp. Paralyzing the prey keeps the prey alive, ensuring a supply of fresh food for the developing wasp.

I have saved the best for last, and it is the story of a parasitic fungus known as Cordyceps, which manipulates the behaviour of its host, often an ant, in order to increase its own chances of reproducing.

The spores of the fungus attach themselves to the external surface of the ant, where they germinate. They then enter the ant’s body through the tracheae (the tubes through which insects breathe), via holes in the exoskeleton called spiracles. Fine fungal filaments called mycelia then start to grow inside the ant’s body cavity, absorbing the host’s soft tissues but avoiding its vital organs so that it stays alive.

When the fungus is ready to reproduce through the creation of spores, the mycelia grow into the ant’s brain. The fungus then produces chemicals which act on the host’s brain and alters its behaviour. This causes the ant to climb up a plant and, upon reaching the top, to clamp its mandibles around a leaf or leaf stem, securing it firmly to what will be its final resting place.

The fungus then devours the ant’s brain, killing the host. The fruiting bodies of the fungus (i.e. the mushrooms) then sprout from the ant’s body, usually the head, through gaps in the joints of the exoskeleton. Once mature, the fruiting bodies burst, releasing clusters of capsules into the air. These in turn explode on their descent, spreading airborne spores over the surrounding area. These spores then infect other ants, completing the life cycle of the fungus. Depending on the species of the Cordyceps fungus and the number of infecting spores, death of an infected insect takes between 4-10 days.

I think it would be hard to dream up something much creepier than this – and to think that it really happens!