The wondrous creatures that share our gardens part I: The creepy crawlies

By Alida Robey

As I peacefully garden, random thoughts about the wildlife I encounter waft through my head. How far does a hedgehog travel in a night? If you throw a snail over the fence, is it likely to find its way back into the garden? How long do worms live?  Rather than continue repeating this cycle of speculation,  I decided to get to the bottom of these little mysteries.

Do those snails make it back over the fence?

There are 43,000 species of Gastropoda (the taxonomic group better known as slugs and snails). There are 220 non-marine species of these mucous crawling critters living in the UK, so it’s small wonder we have such problems with snails in our gardens. Snails can live up to three years. Each snail has both male and female sex organs (they are hermaphrodites) and mating occurs when two entwined snails each shoots a small sperm-carrying dart at the other; each then goes off to lay about 40 eggs.
Garden snail.
Photo credit: Daniela [via Flickr, CC license]
And that burning question….what happens to all those snails that I catapult over my fence? Well yes, snails can happily find their way back over fences and walls, up to a distance of 10 metres. Professor Dave Hodgson, Professor of Ecology, University of Exeter, revealed this fact when he used LED lights and UV paint to track the movement of snails at night in a British garden. The study revealed that snails can travel distances of up to 25 metres during a 24-hour period and reach top speeds of one metre per hour. So you will need to do more than lob them discretely over the wall if you are hoping to do more than just make them work a bit harder for their supper! 

What is the lifespan of a slug?

Most slugs evolved from snails, losing their shells through evolutionary processes over time.
Depending on the species, slugs can live between 1 and 5 years. If you are squeamish about slugs, count your blessings you don’t live in North America where there is the banana slug, which grows to 10 inches long!
The banana slug (Ariolimax columbianus).
Photo credit: Oregon Department of Agriculture [via Flickr, CC license]
Much as we may berate slugs, they do serve an important function in nature, munching up rotting debris and recycling the nutrients back into the food chain. 
However, they also like to munch the tender leaves and stalks of our most treasured little seedlings, and it is for this reason that many British gardeners are keen to shorten the lifespan of these troublesome pests. Use of slug baits is highly controversial and there is insubstantial and conflicting information regarding how these poisons affect other creatures, such as birds and hedgehogs, which are natural predators of slugs. 
Despite being in widespread use, slug pellets are considered by some to be a relatively ineffective method of slug control, some say killing no more than 10% of the slug population in the average garden. Slug pellets fall into 2 main types; those containing metaldehyde or the less common methiocarb.
Metaldehyde is the most common and less toxic form of slug poison and if not taken in too large quantities less likely than methiocarb products to be fatal to other animals – the suggested dose being one pellet every 10 cm (4”). 
Methiocarb is about ten times more poisonous than metaldehyde, and therefore of greater danger to other animals. It breaks down more slowly too, making it a longer lasting hazard in the environment with the potential to affect more animals (targeted or not).
The RHS has some research underway that is due to report in December 2017 on the relative effectiveness of different methods of slug and snail control, including the use of nematodes. This research will help them improve their advice about slug and snail control. 

Does cutting a worm in half make 2 worms?

Sadly no – but thankfully at least one half should still survive. 
Photo credit: Wormwould [via Flickr CC by-NC 2.0]
I always say the common earthworm is the hardest worker in the garden, and Charles Darwin called them ‘nature’s ploughs’. They do an extraordinary job of aerating and fertilising the soil, pulling leaves down beneath the ground at a rapid rate and bringing valuable minerals to the surface with their wormcasts. One acre of land can hold around 3 million earthworms, which are capable of bringing around 9 tonnes of soil to the surface through their wormcasts in just one year. The tunnels they make and live in can go as deep as 1.8 m (6 ft), which enables them to find moisture in times of drought. Worms are capable of digesting even leaves that are generally poisonous, owing to the presence of a chemical in their gut called drilodefensins. Scientists at University College London identified this molecule, which breaks down the toxic chemicals plants produce to deter herbivores. Without this ability, leaves would pile up on the surface of the soil.

Photo credit: danielweiresq
[via Flickr CC by-NC 2.0]

How many spots does a ladybird have? 

Well, actually, there are 40 different species of ladybirds in Britain, with differing numbers of spots and some have yellow wing cases rather than red – the invasive harlequin ladybird (Harmonia axyridis) can also have a black wing case. And no, ladybirds do not gain more spots as they get older. The ladybird is a most welcome addition to the garden as its larvae munch their way through vast quantities of aphids prior to pupating.  However, they have to eat heartily as aphids are so fast at reproducing, they get through three generations for every single generation of ladybird. For this reason, the ladybird’s ability to truly help control aphid infestations has been brought into question.

Is the common wood lice harmful to plants?

An unfortunate name for a little creature that is more closely related (admittedly from way back), to crabs and lobsters! It quietly beavers away eating rotten wood, fungi and garden debris and protects itself from drying up by only coming out from under stones and logs at night. 
Photo credit: Mark Hilditch [via Flickr CC by-NC 2.0]
Woodlice cause little or no damage to plants. Large numbers can be found in compost heaps, where they help break down the plant material and are a useful part of the composting process. But you may well have seen what you think is the same thing around your house. This is a slightly different species of wood louse to the garden variety and is called the pill bug.  It can be distinguished from the woodlouse by its tendency to roll into a tight ball when threatened. Pill bugs are not thought to do any harm in the house although their presence may indicate an issue with dampness, as this is their preferred environment.

How can you tell  the difference between toads and frogs?

I have often wondered how to tell which was which. Frogs generally have a wet, smoother skin, while that of toads is dry and ‘warty.’ Toads walk rather than leap and are less nimble movers than frogs. I regularly help with a garden in Herefordshire where I am frequently surprised by the lump of soil that turns out to be a toad that then ambles off unsteadily down the garden – a frog would have leapt off at the least disturbance. 
Toads return each year to the same pond to spawn their eggs – as many as 7,000 in a sitting.
Frogs come in a much wider range of colours than the steady brown toad with its darker brown blotches; they can be anything from yellow, brown, orange, red, grey, and different shades of speckling. 

What ARE Nematodes?

Caenorhabditis elegans is a nematode that is studied
extensively by scientists.
Photo credit:snickclunk [via Flickr CC by-NC 2.0]
Nematodes are microscopic worms that are naturally present in the soil. They can be purchased in concentrated volumes as biological pest control. There are specific nematodes for each different  garden ‘pest’ such as slugs, vine weevils, ants, chafer grubs, leatherjackets, caterpillars, codling moth etc. An advantage of nematodes is that they don’t persist in the environment like chemicals do – when their prey item depletes, they naturally die off to natural population levels. 
As this is a ‘live’ product, it is currently only available from online suppliers as nematodes have to be used within a few days of purchase. They are sent in a little pack that resembles fresh yeast and one simply has to dilute this to the required level and then water them into the garden. I have used nematodes myself very successfully and believe that with increasing regulatory pressure on toxic sprays and treatments that are harmful to pollinators and other wildlife, nematodes are the way of the future for pest control.
Please leave a comment if you have any questions about the wildlife you encounter in your garden and we’ll do our very best to find an answer. Part 2 will have some common questions about our furred and feathered garden friends.
Alida Robey has a small gardening business in Bristol. For several years in New Zealand she worked with others to support projects to establish composting on both domestic and a ‘city-to-farm’ basis. 

Biological battles in the glasshouses

By Helen Roberts and Nicola Temple

In the calm and serenity of the glasshouses, among the flowering lotus and breathtaking orchids, there is a lethal battle going on – biological warfare between predator and prey. About two months ago, Penny started to use biological control in the glasshouses as a chemical-free means of managing pests like whitefly and aphids. Parasitic wasps and beetles are released in areas of infestation and left to do what comes naturally to them…prey upon pests.
Biological control is a system that has been used by horticulturalists since the early 1800s. The University of Bristol Botanic Garden uses biological controls as it avoids the use of toxic chemicals and also controls pests that have become resistant to pesticide treatment. The method is more economical and certainly more environmentally friendly.
However, it’s not just entirely a simple matter of releasing the predators and then forgetting about it. First, the pests in the greenhouse need to be properly identified and the proper predator controls selected. Then, it’s necessary to release the controls under the right conditions and at a critical time of the season – known as inoculative release – in order for the control to be effective.

A grizzly end for aphids

Aphids have infiltrated the glasshouses at the Botanic Garden.

The Botanic Garden is using two species of parasitic wasps to control a range of aphid species. The story is a grizzly one for the aphid (think the infamous dinner scene in the movie Alien), but with an excellent outcome for plants in the long run! Female Aphidius colemanii and Aphidius ervi seek out their aphid hosts and with incredible precision pierce the aphid’s exoskeleton with their ovipositor and lay an egg directly into the aphid. After a couple of days the aphid dies as it is consumed from the inside by the newly hatched wasp larvae. The larvae then spin a cocoon around the aphid shell and an adult parasitic wasp eventually emerges. These wasps will also control insecticide resistant strains of aphids. Of the two species, A. ervihas a longer life cycle, is larger and will select larger hosts.

The Aphidiusspecies used at the Garden are released as newly emerged adults and are best released when temperatures in the glasshouse are between 15oC to 30oC.

Wiping out whitefly

Encarsia formosa is released on little
discs infused with parasitised scales.
To control whitefly, the Botanic Garden team are using two minute parasitic wasp species, Encarsia formosa and Eretmocerus eremicus. Encarsia formosa controls whitefly populations in much the same way as the parasitic wasps of aphids except they target the whitefly scale, which is the 2nd and 3rd nymph (immature) stage of whitefly, rather than the adult. Adult Encarsia will also feed directly on the whitefly scales. Female Encarsia can lay up to 200 eggs and only a single egg is needed to kill the whitefly. The parasitoids are sold as black parasitised scales that have been fixed onto cards and these are hung under the canopy of the greenhouse plants out of direct sunlight.
Eretmocerus eremicus is slightly different in its approach in that it lays its egg between the whitefly nymph and the leaf surface. Between the 2ndand 4th nymph stage, whitefly are sessile, and so when the egg hatches after 4 days, the wasp larva attaches its hook-like mouthparts to the underside of the whitefly scale and starts to chew. After about 4 days of chewing, the parasitoid larva crawls into the body of the whitefly scale and just sits there biding its time until the whitefly starts to pupate. When the pupation phase begins, the parasitoid releases enzymes that begin to digest the insides of the whitefly and this will be the wasp larva’s last meal before it begins its transition to adulthood – a process that takes about 12 days. The adult wasp chews its way out of the remains of the whitefly scale and the cycle begins all over again.

Making meals of mealy bugs

Cryptolaemus montrouzieri is a small ladybird species that is used in the control of mealy bug. Its larval stage looks like the mealy bugs they prey on, which is a case of aggressive mimicry. Eggs are laid in amongst the cottony egg sacks
of mealy bugs and the eggs hatch after 5 days. The three larval stages of the beetle and the adults will feed on mealybug eggs, young crawlers, and the honeydew produced by mealybugs.
Adults are released onto infested plants in the evening and can be encouraged to stay in an area by using netting. These predators will also eat aphids and other scale insects if their prey of choice is in short supply.

Not all biological warfare goes to plan

As previously mentioned, the use of biological controls has many advantages, including reduced costs, reduced dependence on harmful chemicals and reduced potential for pests developing pesticide resistance. However, human interference in the predator-prey relationship doesn’t always go to plan.

One famous example is the introduction of the cane toad to Australia. These were introduced in 1935 to control the Greyback cane beetle that was destroying sugar cane crops. Essentially not enough was known about the cane toad and how it interacted with the target beetle; the two species are not compatible at all in terms of a predator-prey relationship. The beetle feeds at the top of the sugar cane stalks but the cane toad can neither climb nor fly and therefore cannot reach the beetle. The toad moved in to other areas besides sugar cane and spread like wild fire. They are productive breeders, which combined with a lack of predators due to their high toxicity, led to a population explosion. Its feeding habits are highly non-specific – it will just about eat anything that it can stuff into its mouth. Their introduction, despite the best of intentions, was an unmitigated disaster. This was one example that showed just how wrong biological control can go if not researched thoroughly.
However, rest assured the Botanic Garden will not be releasing anything but well-researched and proven beneficial insects into the glasshouses. When done properly, biological control is a highly effective strategy for managing pests.