Sterilising Cork and Looking Out for Alien Insect Species

Things to look our for when you’re setting up a new Terrarium

I’m currently in the process of setting up a new terrarium, which is very exciting!  Don’t worry, I’ll take you on a tour of my new Tall Orchidarium in due course.  However, today I wanted to tell you about something unexpected that happened to me, while I was gathering together the materials for this new enclosure.

I recently purchased some large sheets of natural cork for my Tall Orchidarium.  When the cork arrived home, I found some unexpected and unwanted gate-crashers – a non-native species of ant, known by its scientific name of Crematogaster scutellaris.  These ants are also called acrobat ants, but as they’re found in numerous countries, I’m sure that Crematogaster scutellaris ants are known by many other common names, too.

Crematogaster scutellaris is an ant species that’s found in the Mediterranean, North Africa, Italy, Austria, Germany, Croatia, Bosnia and Herzegovina, and France.  This is not an ant species that’s naturally found in the UK; any Crematogaster scutellaris ants that are discovered in Great Britain, will have been transported here by man.

Check any insects you find

I suspect that these ants made their nest inside a section of cork bark, back in their home country; before the cork that housed their nest was stripped from the tree and packaged up, ready to be shipped to the UK.  But whatever happened, I am sure that these ants were accidentally transported to the UK, along with a delivery of cork that was destined to be sold for terrariums and other projects.  I purchased a large quantity of this cork, which was how I came to be in possession of this colony of Crematogaster scutellaris ants!

Crematogaster scutellaris is a species of ant from the Mediterranean, North Africa, Italy, Austria, Germany, Croatia, Bosnia and Herzegovina, and France.

Crematogaster scutellaris ants

It’s possible that other cork deliveries have arrived in the UK with Crematogaster scutellaris ants stowing away inside the bark; so I wanted to write about my experience – to raise awareness and to help you – if you, or your friends or family, find yourselves in the same predicament.

It’s important to check over any cork before you make a purchase.  If you find any unusual insects, please report them to your cork supplier, so they can take prompt action to prevent the insects from escaping into the wider landscape.

Non-native ants and insects

Although Crematogaster scutellaris is a commonly found ant in its native range, this insect is not native to the UK.  It can be harmful, or even catastrophic to introduce a non-native species to an unfamiliar environment, as the new species may negatively affect or out compete native wildlife, unbalance an ecosystem, or damage plants or habitats.  Non-native species can have a disastrous impact on the ecosystem they’re introduced to.  Acrobat ants create nests that can house up to several thousand worker ants; so if you find one ant, it’s likely that there are more ants nearby.

Accurately identify insects

My close up photographs make this ant appear monstrously large, but in reality there’s nothing giant about Crematogaster scutellaris ants – it’s just a regular sized ant that’s comparable with the size of our commonly seen, native UK ants.  Although I must say, that since discovering these ants, I have seen varying sizes of Crematogaster scutellaris ants, inside my home, but they’ve not been alarmingly large in size, as they might appear in my pictures!  Naturally, Crematogaster scutellaris queens stand out as being larger in size, but so far I’ve not found a queen.

Crematogaster scutellaris pictured on the Amesiella monticola flowers, inside my Rainforest Terrarium, on the 20th November 2020. 

If you’ve seen ants or any other insects on your cork bark, it’s important to check that your terrarium has not become a home to any unwanted non-native insects or any plant pests.  As you can see in my photographs, Crematogaster scutellaris ants are distinctive in that they have amber coloured heads and pointed gasters or abdomens.

If you’ve spotted any insects, it’s important to identify what insect you’re dealing with.  Many insects live inside terrariums and in or around cork, so if you find an insect, it may well not be a pest, an invasive species, or anything to worry about.  You might find it easier to take a photograph, to help you accurately establish what insects you’ve found.  Having a photograph is so helpful, as you can zoom in to assess the insect’s features or clarify your identification with an entomologist.

How to report sightings of Crematogaster scutellaris and other non-native species

If you come across Crematogaster scutellaris or indeed any non-native species, please record your sightings on the Biological Records Centre’s form – here’s a link.

What to do if you find Crematogaster scutellaris ants

After discovering these Crematogaster scutellaris ants on my cork, I notified the supplier where I purchased my cork to alert them to the problem.  I set up an ant trap inside my Tall Orchidarium, one near my Rainforest Terrarium, and another in my bedroom.  We’ve also put an ant trap in the car that was used to collect the cork.

  • If you discover any Crematogaster scutellaris ants, please act promptly.
  • Contact your cork supplier to alert them to the problem.  Please take action to contact your supplier even if you made your purchase a considerable while ago.  It’s important to make your supplier aware, so that they can take action to prevent this ant species spreading – there may be more ants lodging within their stock of cork or inside their store cupboard.
  • As with any non-native species, please record your sightings on the Biological Records Centre’s form – here’s a link.
  • Use ant traps to prevent any Crematogaster scutellaris ants from establishing themselves in your area.
  • Crematogaster scutellaris ants hibernate during autumn and winter.  If you spot any of these ants during autumn or wintertime, it’s important to set up ant traps right away and keep the traps going over the autumn and winter months.  But it’s just as important to remember to put fresh ant traps out in springtime, when the ants will begin to emerge after hibernation.
  • The ant traps will ideally need to remain in place through the summer months, as new Crematogaster scutellaris ants emerge from mid to late summertime.
  • Please check that your ant traps are viable.  Regularly check your ant traps, to ensure that they contain sufficient ant bait.
  • Once you’ve discovered Crematogaster scutellaris ants, you’ll need to remain vigilant to prevent these ants from establishing in your area.  I’d recommend regular and thorough ant checks and the continual use of ant traps, for a period of a year.

I’ve used traps that contain an ant killing poison.  The worker ants will collect the bait and take the poison back to their nest; the ants then consume the bait and die, which sounds awful, I know.  I must be honest, I feel pretty dreadful about killing these ants – after all these Crematogaster scutellaris ants didn’t choose to relocate to the UK, they didn’t choose this situation.  However, it’s important to take steps to prevent this non-native species from escaping and establishing themselves here in the UK, as the introduction of a non-native species can upset the balance of nature and cause significant harm.  We need to protect our native ant species as well as other UK insects and habitats.

This isn’t a problem that can be solved overnight.  I’m still finding Crematogaster scutellaris ants everyday.  I’ve seen ants on the orchids that are growing inside my Rainforest Terrarium and on plants inside my other terrariums, as well as inside my new Tall Orchidarium.

Cork production

Cork is the bark of the cork oak – Quercus suber – a marvellous evergreen tree that grows in Portugal, Spain, Algeria, Italy, Morocco, Tunisia, and France.  Quercus suber trees really are incredible!  Once a tree has been growing for around twenty-five years, it will have formed a specimen tree, with a sufficiently large enough trunk to produce its first cork harvest.  Cork bark is harvested by hand, from living trees; skilled workers expertly remove the tree’s outer layer of bark, taking care to leave the tree’s cork cambium layer intact.  The thin layer of bark that remains will protect the inner workings of the Quercus suber tree and allow the tree to continue living and growing.  After another nine to thirteen years have passed, the tree’s bark will have re-grown and a second cork harvest can then be obtained from the same tree.  Quercus suber trees usually produce twelve harvests of cork in their lifetime!

Protect Quercus suber forests

The forests where Quercus suber trees grow are home to numerous woodland plants and trees.  These species rich woodlands are home to all manner of wildlife, including rare and endangered species.  Cork produces a sustainable harvest and provides employment for local people.  Quercus suber trees form an important part of the landscape.

Support the cork industry

Wine producers who continue to purchase corks to seal their bottles are using a sustainable practice.  Whereas wine producers whose bottles are sealed with plastic, are not.  If you purchase alcohol from companies who seal their bottles with cork, you’ll help to safeguard the future of cork production and in turn you’ll be protecting the important conservation areas, where Quercus suber trees grow.

Purchasing cork for terrariums

I always purchase fresh cork bark that hasn’t been used before.  I don’t want to use cork that has previously had plants growing on it, or cork that has been used inside another terrarium or vivarium – just in case the cork comes with any pests, diseases, or mould.  Consequently, to avoid any problems, I purchase brand new, fresh cork to use to mount my epiphytic plants.

Virgin cork

The term, ‘virgin cork’ means different things to different people.  Many hobbyists use the term, ‘virgin cork’ to describe cork that hasn’t been used  before, but this term is also used to describe a Quercus suber tree’s first harvest of cork bark.  The first two harvests a Quercus suber tree produces will be inferior to the quality of cork bark that more established trees produce, but these initial harvests will yield useful pieces of cork, ideal for terrariums, orchidariums, and vivariums.

When you are selecting cork to mount orchids, ferns, or other plants, look for pieces of cork bark that will be an appropriate size for the plant you are mounting.  Remember – you don’t want to have to re-mount your plant in a couple of years’ time – so if you know that your plant will eventually grow to form a large or substantial plant – choose a larger piece of cork to mount your plant.

How to sterilise cork bark

There are a number of ways that you can sterilise cork bark.  I’ve often frozen cork in the freezer for a few days; then I’ve boiled the cork, and finally I’ve baked it in the oven!  Please note, if you take any of these steps to use heat to sterilise your cork, you will need to watch your cork the entire time you’re heating it – so that if your cork starts burning, you will be on hand to turn the oven or stove off immediately and take responsive action.  If you’re a child, please ask an adult to assist you, as this could be dangerous – I’d hate for you to come to any harm – so please take great care of yourselves.  However you sterilise your cork, it’s wise to watch the cork and check it regularly.

  • The easiest step is to freeze your cork in a freezer, but this might not be as effective as boiling, steaming, etc, as many insects can survive freezing temperatures, even for extended periods, as many insects hibernate.  Cork also has insulating properties, helping any insects sheltering inside to resist the cold.
  • You can also sterilise cork bark by boiling it or steaming it in a large pan of water.
  • You could also use a hand held steam cleaner to sterilise the surface of your piece of cork bark.  If you have a large piece of cork that won’t fit in a cauldron or in the oven, then this is a great option.  Move the nozzle that delivers the steam, over the cork, taking care to clean the front, back, and sides of the section of cork.
  • Then you can bake the cork in the oven.
  • NB. please make sure that you closely monitor your cork if you’re baking, steaming, or boiling it – just in case you burn the cork.
  • You can microwave cork – but please check your cork over thoroughly prior to microwaving, as prices or labels are often attached to cork bark with metal staples.  It’s very dangerous to place metal in a microwave.  Please only microwave a piece of cork, when you are at least 100% certain that there are no staples, pins, wires, or any metal, hidden inside your piece of cork.
  • It’s hard to give timings for these methods, as cork naturally varies in its thickness and condition.  Needless to say, the thicker a section of cork is, the harder it is to sterilise; you’ll need to boil or bake thicker pieces of cork for a longer period of time than you need to devote to treating thinner sections of cork.  I’ve boiled cork for between twenty minutes to an hour.  The time I’ve spent baking cork in the oven has also varied dramatically.
  • The important thing to say is that it is vital that you’re on hand to monitor your cork, while you’re boiling, baking, or steaming it.  I hope these tips help you – good luck!

Other articles that may interest you if you’re setting up a bottle garden, a terrarium, vivarium, or orchidarium…………….

To see my Tall Orchidarium being set up, please click here.

To see a planting list with photographs and lots of information about orchids, ferns, and other plants that thrive inside terrariums, vivariums, and bottle gardens, please click here.

To see my Rainforest Terrarium being set up, please click here.

For ideas of how to protect your houseplants and terrarium plants from spider mites, please click here.

To see the first instalment of my White Orchid Trial, please click here.

To see the first instalment from my Madagascar Terrarium, please click here.

To see the first instalment from my Miniature Orchid Trial Terrarium, please click here.

To see my Orchidarium being set up, please click here.

To see my step-by-step guide to planting up a terrarium or bottle garden, please click here.

To see all of my articles about setting up a terrarium, please click here.

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