I’ve been contemplating for a while what topic to cover this week, but after seeing this bumble bee getting particularly interested in a frond of bracken, I decided I’d have a look into the wonderful world of ferns, a habitat which I see on virtually every walk over the summer months.
Ferns occur all over the UK. Though there are different species, the most common is bracken, and that tends to be what people think of when they think of ferns. Bracken is a very competitive plant. It spreads extremely easily, as it releases spores, rather than seeds, which travel on the wind, and can germinate in a wide variety of habitats. A new plant can also grow from a fragment of root, so once bracken has settled in an area, it’s extremely difficult to get rid of. Unfortunately this means that bracken poses a serious threat to habitats such as heath land, which is rare and endangered habitat in the UK.
Not only is bracken a nuisance, but it’s also carcinogenic (can cause/encourage cancer) when eaten. That’s not too much of a problem for humans (though in some countries it is considered a delicacy!), but if domestic animals feed on it, they can be at serious risk. More of a threat to humans, are ticks, tiny arachnids which feed on blood. As deer, sheep, cattle, and other large mammals pass through patches of bracken, ticks hop off them, and onto the ferns. When humans (or other large mammals) walk through the ferns, these ticks hop on, and start drinking blood. This in itself isn’t really a problem, however ticks can carry Lyme’s disease, which can kill people… which of course isn’t great. Therefore as a walker, if you pass through a lot of ferns, it’s well worth checking yourself (particularly arms, legs, and neck) for these tiny black spots.
So all in all, bracken doesn’t seem that great for anyone involved… except the ticks I suppose, it’s not even fed upon by many other organisms, and tends to outcompete virtually every other form of plant life. However bracken does form a damp dark under layer, which may be inviting to a range of invertebrates, and certainly on my wander I found a few different invertebrates sitting on and around the bracken.
But this leads us back to what originally intrigued me about the bracken. What was that bumble bee so enthralled with? Well it turns out that the underside of the fronds have glands which secrete a sweet liquid (nectar) which is attractive to insects. Of course flowering plants use nectar to attract insects for pollination… but bracken doesn’t have flowers, and it doesn’t need seeds dispersing, so why does it secrete nectar? Well in my wanders through various sources, I can’t find anything to explain why it would be. The best hypothesis I can think of is that provision of nectar might bribe insects (such as ants) to protect the fern from attack, though loaded with all those toxins, I don’t know that this kind of defence is strictly necessary, so it seems a relatively unlikely answer.
So I end with a question. Do you know why ferns secrete nectar? Do you have an alternative hypothesis? It must be secreted for a reason; plants don’t just waste resources like that for no reason.