How To Keep Bees And Butterflies Out Of The Greenhouse

I thought I would share the following query and my response, to help other visitors:


Hi
We have a new greenhouse that we built earlier in the year.  It has been very hot lately, and we want to keep the greenhouse door open.  The problem is that bees and even butterflies sometimes enter the greenhouse, and have difficulty finding their way out.  My wife tries help them out but it isn't easy, and it's hot in there!

Do you have any tips as to how we can keep bees and butterflies out of the greenhouse?

- Steve, UK

How To Stop Bees And Butterflies Getting Into The Greenhouse

Below you can see my simple method for keeping bees and butterflies out of the greenhouse.  We open the greenhouse door, and use pegs to attach a piece of netting in front of the opening. 

This keeps bees and butterflies out, but allows the door to remain open. 

The netting was left behind in the garage when we moved into the house, and for some time, it was used for keeping leaves out of the pond.  A recycled net curtain would also do the trick.

Why is it a good idea to keep bees and butterflies out of the greenhouse in domestic situations?

Personally, I am very keen to keep bees and butterflies out, for 2 key reasons:

1. Bees and butterflies can easily become trapped in spider webs
Although I have advice on how to rescue a bee from a spider web, prevention is better than cure!  We might not always be on hand to perform rescues and even if they are removed, new webs can be created by spiders overnight! 

2. Nutrition deprivation
If bees or butterflies become trapped overnight, they may be deprived of vital energy from food (nectar and pollen). This is because the food resources on offer in the average domestic greenhouse probably would not be sufficient to sustain a bee or butterfly adequately for very long, and increases the risk of entrapment in spider webs.

In the case of social bee species such as bumble bees, it would also mean the foraging bee is unable return to the colony with food for developing larvae back at the nest.

Bees need to make hundreds of visits to flowers every day in order to gather the nutrients they need in the form of nectar and pollen.  They need to be able to forage freely.

Do I need bees in my greenhouse to pollinate crops?

Commercial growers may use bees - especially bumble bees, to pollinate greenhouse-grown food crops, such as tomatoes. 

However, whilst this may be important for commercial growers with vast greenhouses and polytunnels, I find this is not necessary for domestic situations.  Any increase thanks to pollination by bumble bees is, in my view, primarily apparent because of the scale. 

Thus, even a tiny percentage increase in crop production could be significant in volume terms for large growers, but would be negligible even in a large garden greenhouse.

As I write, I have been growing tomatoes etc in my greenhouse for 10 years, and have found that sufficient crops are grown for our needs without endangering bees and other pollinators.  I have more than enough tomatoes to pass around or freeze for use in pasta dishes and casseroles later in the year.

Therefore, I am happy to keep bees and butterflies safely out of my greenhouse!

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