Appreciating Ivy

Ivy flowers. Copyright: Alfred Osterloh

With great pride I support our English Ivy (Hedera Helix). I think that in the right situation it's a feast for the eyes and a wonderful resource for all of nature - us included. Ever since I was a lad I'd heard all the negative press about ivy being parasitic (which it's not) and that it damages everything it climbs upon (which it does not), so earlier this year I did my own research and documented the most current findings on the positives and negatives of ivy and how to manage ivy on my blog here. I also wrote about research into the weak, but potentially important, adhesion that ivy rootlets secrete here.

With that in mind, I was very excited to read research published earlier this year evaluating the importance of ivy (Hedera helix and H. hibernica) for autumn flower-visiting insects, particularly honey bees. Not only were the findings positive, but the researchers went as far as to say that:

'ivy may well be a keystone species for flowervisiting insects in autumn'  
(Garbuzov & Ratnieks, 2013)

Keystone species are species that play a crucial role within the ecosystem(s) that they are present. Keystone species can affect many other organisms within the ecosystem to the point of determining the numbers and types of other species within the ecosystem community.


To see why the researchers have made this suggestion, we need to consider which species visit the ivy flowers, what the ivy flower offers, and what benefit these species derive from a relationship with ivy:

• Firstly, there were many different species visiting the flowers of the ivy including the honey bee (Apis mellifera), common wasp (Vespula vulgaris), ivy bee (Colletes hederae), hover fly (Eristalis tenax), green bottle fly (Lucilia sp.) and red admiral butterfly (Venessa atalanta) among others.

• Secondly, the ivy flower offers both nectar and pollen, possibly no surprise there. But, perhaps what is surprising is that the nectar has a sugar content of around 49%. This is quite a high percentage and shows that ivy nectar is a high quality foraging resource. The results strongly suggested that the only nectar that the tested bees had in their crops was from ivy. This becomes even more important considering that 79.7% of honey bees and 94.6% of bumble bees did not have pollen in their baskets. Pollen trapping at six hives in two locations showed that of the pollen that was collected by the honey bees, an average of 89% was pollen from ivy during the autumn.

• Thirdly, ivy is a very abundant plant meaning that foraging distances are much shorter than summer foraging trips. Collecting pollen and nectar from ivy flowers is also fairly easy. These traits make it efficient enough for honey bees to make a honey crop. This may improve survival over winter of honey bees. These factors may well provide honey bees with a food resource allowing them to rear young workers before overwintering, subsequently providing them to get off to a great start in the spring. The paper rightly suggests that further experimental work should be done before we can understand this properly.

So, while we already knew that ivy provides food via berries and can provide a home for many insects and nesting sites for birds (if it is allowed to grow), but this paper really drives home the importance of ivy to many species of insect that are still around in autumn, including late season butterflies.

Ivy not only provides them with a meal as they collect nectar or pollen, but the nectar is of such high quality it can also help honey bees survive the winter. Without sounding too dramatic, if ivy was lost to the ecosystem, even locally, it could mean death to the honey bees in that particular area. If honey bees aren't around to pollinate our food crops, then we could be in big trouble.

It just goes to show how difficult it can be to understand ecosystems and food webs, prior to this research I wouldn't have connected ivy to food crops and yet the honey bee is a link between the two.

For further information on this paper

• Watch a video made by the University of Sussex produced to assist us in identifying the insects we may see on ivy flower:

• To read more, view some amazing macro shot, or download an ID leaflet; see the University of Sussex blog post about the research here.
• Read the AOB blog post that alerted me to this research.
• Also, interestingly, a house that had been allowed to be overrun by ivy for 10 years recently had the ivy trimmed back. While some of the dead ivy branches were left hanging for some reason, this house shows that as long as the masonry and brickwork aren't damaged prior to the ivy - then they won't be damaged by the ivy. To see the photos, click here. 

Reference
Garbuzov M., Ratnieks F.L.W., Leather S.R. & Roubik D. (2013). Ivy: an underappreciated key resource to flower-visiting insects in autumn, Insect Conservation and Diversity, n/a-n/a. DOI: 10.1111/icad.12033