Intimate Relationships

The world of invertebrates is a web of relationships with plants and other animals. Intimate relations between some invertebrates and other organisms have evolved to become so intricate that they are dependant upon each other for survival.

Disguised as a flower, this crab spider (Thomisus onustus) easily catches a visiting bee © Dragisa Savic

Ants and Plants!

Take for example the bull's horn acacia - a tree which grows in the plains of Central America . This tree has a rather special relationship with ants from the group Pseudomyrmex. The tree provides a living home for the colony and the ants in turn protect the tree from being eaten by grazing herbivores. Both the ants and the trees benefit from this association; the ants get protection and shelter and the trees are protected from being eaten.

How does this relationship actually work?

The ant colony live within the trees swollen thorns and feed upon a special sugary liquid secreted by the tree from special tissues called foliar nectarines. Once the colony is large enough it will patrol the tree day and night attacking and stinging anything which tries to feed upon it. These ants may also prevent the encroachment of other vegetation around the base of the tree, allowing it more access to soil nutrients and light.

Galls Wasps and Oak Trees

The Gall wasps are another group of insects with an intimate relationship with trees. The wasps lay their eggs in a specific part of a tree such as a leaf stem or bud; Oak are a favourite type of tree used by wasps within the cynipid family. The oak apple gall wasp Biorhiza pallida lays her eggs in a leaf bud. Once in the tissues of the tree chemicals are produced by the larvae which make the tree tissues grow in a very specific way. In this case an apple-like growth is formed, within which there is about thirty chambers each with a larva inside, these can be seen between May and June. Galls typically have three layers; the inner layer is thought to secrete nutrients on which the larvae feed. Each different species of wasp can be identified by the type of gall produced by the tree and one tree may have many different species of wasps developing within it, there is even one gall called the witch's hat due to its long pointy shape! The tree is unlikely to gain from this relationship as the wasps are high-jacking its resources to benefit their own larva and don't give anything back in return.

Oak apples courtesy of the gall wasp (Cynips quercusfolii) © Dragiša Savic

Amazing!

There are a group of inquiline wasps that parasitise the gall wasps larvae within their galls. By laying a number of eggs within an already formed gall their larva can kill the rightful inhabitant and take over the gall.

STAR FILE: Fairy Fly

In Programme 4 of Life In The Undergrowth David Attenborough encountered the largest insect on earth the mighty Titan beetle! This week it's the turn of one of the smallest. Fairy flies are thought to be the smallest of all insects. The largest has a mighty wing span of 3mm; whilst the wing span of the smallest, a fairy fly called Alaptus magnanimus, is just 0.2mm! Although called flies, they are in fact tiny parasitic wasps (Family Myrmaridae) belonging to the insect order Hymenoptera which includes bees, wasps and ants. They lay their eggs inside the eggs of other insects. Not surprisingly they are not strong flyers and they tend to be carried along on air currents and are carried into houses in spring and summer. They have unusual hairy paddle-shaped wings.

Ants, Aphids and Ladybirds

An interesting intimate relationship between invertebrates is that of ants, aphids and ladybirds. Some ant species, such as the common Black garden ants (Lasius niger) found in the UK, farm aphids. They have aphid livestock which they transport between plants and protect from enemies in return for a sugary substance called honeydew, excreted from the aphids as they suck on plant sap. Adult ladybirds, and their larvae like to eat aphids, you will often see them hoovering them up as they walk along a plant stem. So, most days in the summer you can see an interesting intimate relationship for yourself just by having a close look at the goings on in your back garden!

7-spot ladybirds munching on black aphids © John Feltwell

Invertebrates in Danger! - Oil Beetles

Violet oil beetle (Meloe violaceous) © David Fenwick

British oil beetles; so called because of the oil they secrete from their joints to deter predators, have one of the most extraordinary life cycles of any British insect. A female adult oil beetle burrows in sandy areas close to a solitary bee colony. Within the burrow she will lay about 1000 eggs which take one year to develop. Once hatched the larvae are very active and louse like, and for good reason. In order to survive and reach maturity they must immediately find a bee and hitch a ride on its back. To have the best chance of meeting a bee the larvae climb up flower stems often lying in wait within a flower itself. A bee collecting pollen for its own nest, may unwittingly become covered in the oil beetle larvae, secured by their specially-adapted hooked feet. Once in the bee's nest the larva disembarks and set about eating the bee's eggs. Following this meal, the oil beetle larva develops into a more regular grub like stage which then consumes the stored pollen. The larvae pupate within the bee nest until the following year, when they emerge as adult oil beetles ready to mate and start the whole cycle again.

Why are they disappearing?

Oil beetles are declining in Britain . Of the nine species once found within Britain four have become extinct and two have not been seen since the 1950s, in fact only three species have been seen recently. This is thought to be mainly due to loss of habitat, particularly heath and grassland, through human influence. Changes in land use for forestry and farming have reduced the number and quality of available nesting sites both for the beetles and the solitary bees they rely upon.

Where can you still find them?

The 2 most common species are the Violet oil beetle Meloe violaceus and the Black oil beetle Meloe proscarabaeus. These species are slow moving, flightless with overlapping wing cases and kinked antennae. The Black oil beetle is the most common but is only to be found in the South West of England and Wales . The Violet oil beetle can be found as north as Sutherland in Scotland and is widespread over the west side of Britain . You are most likely to come across an oil beetle in late March to early April, walking along paths, adults tend to range from 10mm to 30mm in size.

"Whenever I hear of the capture of rare beetles, I feel like an old war-horse at the sound of a trumpet" - Charles Darwin

Intimate relations with humans

Invertebrates are essential. They are an integral part of the functioning of our planet's ecosystems. Without invertebrates the life support systems of our planet would collapse. However, we often forget, disregard, neglect, or harm them. Invertebrate conservation is of vital importance for the future health of the planet and the survival of many of its species, including us. Without invertebrates there would be no Giant Pandas, no Orangutans, no Blue Whales, no rare orchids, and no Albatrosses.

Healthy, fertile soils – courtesy of earthworms © Roger Key

Without invertebrates we would be in big trouble. Here are just a few of the benefits that invertebrates bring to humans:

• Pollination a large proportion of the crops that we grow are pollinated by invertebrates, without them we would have no apples, strawberries, tomatoes.
  
• Healthy soils it has been estimated that earthworms provide us with more than 16 billion worth of topsoil around the world every year.
  
• Pest control some invertebrates like to eat the crops that we grow, and as a result they can cause a lot of damage. However, there are a lot of other invertebrates out there who like to feed on these pests, they help to keep the numbers of things likes aphids down, and keep the natural balance.
  
• Flowers all the flowers that we love to look at or smell are only like that because of invertebrates. They have developed these traits to attract their invertebrate pollinators, and without them, the world would be a duller place.
  
• Food for other animals as mentioned above, an enormous number of birds, mammals, reptiles and fish all eat invertebrates.
  
• Cleaning services invertebrates like dung beetles clean up after us. They help to break down organic waste, and aid in the recycling of nutrients. If there were no dung beetles the great plains of Africa would be overwhelmed with piles of dung!
  

Not only do invertebrate provide all of these natural services to humans, they do it all for free!

Free pollination and pest control services courtesy of the hoverfly (Chrysotoxum bicinctum) © Nigel Jones

Invertebrates in Danger!

Unfortunately, due to the activities of humans on this planet, many species of invertebrate are in big trouble. Through the loss of wild areas to housing, industry, agriculture or forestry we are destroying the habitats that invertebrates depend upon to survive. Through the release of pollutants into the environment in the form of insecticides or industrial wastes, we are poisoning healthy ecosystems and killing populations of invertebrates. Through the insensitive management of land we are damaging invertebrate habitats.

• Over 50% of dragonfly, grasshopper and butterfly species in the UK are declining.
  
• In the last 15 years 3 species of invertebrate have become extinct in the UK .
  
• One of these species, Ivell's sea anemone (Edwardsia Ivelli ) was a global extinction.
  
• In the UK it is estimated that 1260 invertebrate species have become extinct in last 100 years.
  
• In addition to these, 226 species of beetle have not been seen since 1970.

Essex Emerald moth (Thetidia smaragdaria maritima) now extinct in the UK © Roger Key

Invertebrates need your help!

However, the interactions between humans and invertebrates can be positive as well as negative. Negative interactions often occur through lack of knowledge of invertebrates and their habits; we can reduce our negative interactions by promoting the protection and highlighting the importance of invertebrates.

Now that you have watched Life in the Undergrowth and learnt how amazing invertebrates are, spread the word! We can all make a difference to give invertebrates a helping hand. Next time you reach for the slug pellets stop and think of the friendly invertebrates that you will also be killing. Next time you go to swat that wasp have a closer look it may be a friendly hoverfly. Next time you cut your lawn, how about leaving part of it to grow a bit longer and rougher for grasshoppers? Why not let one corner of your garden go completely wild, or plant wildflowers for bumblebees?