New Pond Mining Wasp Invasion

[Bakerman28]

I am slowly constructing a garden pond, stream, and deeper pool. It has been going on for quite some time. Over the last few months I have been shaping the soil around the pond and noticed several small mounds with a hole in the centre. These mounds are on the flat 'stream' bed, up the pond sides, even in the near vertical walls of the pond. Through this forum I identified that it is a mining wasp - Mellinus arvensis. Many thanks for the helpful photos.

Before I knew what the insects were - there are many, many holes - I started lining the pond with a layer of clay. These wasps were undeterred and carried on mining little holes.

I intend to line the pond with a stone proof/weed proof membrane, then carpet underlay, then rubberised pond liner. I read from the forum about their egg chambers being up to 40 cms underground, and that the wasps can survive well into the Winter.

My question is, will the newly hatched wasps tunnel through the membrane, underlay, and pool liner on their way out? It would be a disaster to have holes in the pool liner after all my hard work.

Any advice would be welcome.

[southlonder]

I am not sure.

However personally I would try to time putting the pond layer for when they have all emerged, if possible.

[Bakerman28]

Thanks for this idea, southlonder. This would be the best way forward if someone could tell me when abouts will the new wasps finish emerging as I can't find that info anywhere.

[JRsbugs]

I have a feeling the wasps will remain in the ground until you see them the following year, which is around August! As with any insect, once emerged they start reproducing.

I have these, and I try to accommodate them, they are a very useful wasp to have around. They take flies to the nest, and they make several nests in one bed I have but also in surrounding edges of beds. I find they will make nests often at the edges of beds so I leave any long grass so as not to disturb them.

I found an account of how they make their nests (further down the page).

Bug Eric: Wasp Wednesday: Mellinus

If you put your liner etc. on top of the nests, and if they do happen to find their way through the liner not only will they be drowned but your pond will have lots of holes in the liner! I wonder if they would find their way out to the side of the pond, but if that was some distance it might be unachievable and I imagine their instincts would be to go straight up.

It seems you have a problem, these wasps have very sharp mandibles. It would be a shame to harm them. All I can suggest is to wait until you see them next year, that might not all be at once as usually males emerge before females. The earlist photos I have of males last year was on 13th August, they were about at around the same time this year and I spotted a female soon after seeing a male. If you are prepared to wait that long, then put your liner in place pronto before they start to make more nests you might be successful. They tend to nest in the same place each year.

[Bakerman28]

Wow, many thanks JRsbugs. You have given me so much info that I can begin to determine what I will do.

As you say they are a wasp to keep. The wasps appear to be very unlike the common or german wasps. They are docile, a little like hover flies, a totally different shape to 'wasps' and very quick when they move. I figured that if they were able to tunnel through soil then they must have some mighty equipment (thanks for the info on their mandibles).

Many thanks to the Forum for advice and guidance on this tricky situation.

[southlonder]

Originally Posted by Bakerman28

Wow, many thanks JRsbugs. You have given me so much info that I can begin to determine what I will do.

As you say they are a wasp to keep. The wasps appear to be very unlike the common or german wasps. They are docile, a little like hover flies, a totally different shape to 'wasps' and very quick when they move. I figured that if they were able to tunnel through soil then they must have some mighty equipment (thanks for the info on their mandibles).

Many thanks to the Forum for advice and guidance on this tricky situation.

Good luck - I don't think they can sting people.

[King Edward]

If you use thick Polyfelt T60 woven underlay (I bought mine here when I did my pond recently), I suspect it would be quite difficult for the wasps to tunnel though (wouldn't like to guarantee that though). You could perhaps try to dig out as many of the nests as possible (if they're not too deep) when you're ready to start putting down the liner/underlay - you don't really want to wait a whole year before finishing the pond, only to find they start nesting again next year.