On Friday we posted a gallery of grey squirrels, an invasive alien species that has almost completely replaced our native squirrel population. Unfortunately, our native bluebell (Hyacinthoides non-scripta) is also being threatened by the spread of an invasive alien: Spanish squill (Hyacinthoides hispanica), a similar bluebell species imported into our gardens from southern Europe during the 17th and 18th centuries.
Our native bluebells are dark blue and fragrant, with flowers on just one side of the stem producing that characteristic droop; the stem and the leaves are slim and flexible. Squills’ flowers are lighter in colour, often striped, and can be white or pink as well as blue. The whole plant is more upright; the stem and leaves more robust.
Bluebell 
Spanish squill
The two species are genetically so similar that they cross pollinate, producing a hybrid. Hybrids are usually weaker, less successful than the parent-species, and infertile – but not in this case. The Hyacinthoides hybrid is tough, adaptable and very fertile; it produces more seed than either bluebell or squill and that seed germinates more easily and in a much wider range of conditions.
The Woodland Trust has estimated that one in every six of our bluebell woods has been invaded by Spanish squill and the resulting hybrids are out-competing the bluebells. Climate change is already threatening the delicately balanced environment in which bluebells thrive; the pressure of an alien competitor for that changing environment could be very damaging.
Ian, a Friend of SCP, found Spanish squill among the bluebells in the copse at the bottom of Sheep Field several years ago. Each spring since then, he has conscientiously pulled out or dug up the squill flowers to stop them seeding or cross pollinating. Last year he reported that there were no squill flowers in the copse, though this does not necessarily mean there are no squill bulbs below ground. Let’s hope his report this year will be as positive.
We really do have to be more careful about moving species around the world for our own purposes.
Header photograph: DKG
Other photographs: Google Images
Here’s another alien invasive species, introduced originally as pest control but now a serious threat to our native ladybirds.
Southwick Country Park Nature Reserve 
When we moved to Southwick in 2019 parts of our garden had already been planted with a mixture of bluebells and Spanish squill. Too many to remove I’m afraid but we are careful not to let them escape from our garden and try to remove many of the squill seed heads. The bluebells are managing to hold their own so far!
I am afraid that digging up the bulbs and assiduous dead heading to prevent seeding is the only way to do it.