How do I seal against flies from attic insulation around a load-bearing beam?

[sizz]

I have supported a couple of rafters with a substantial beam, and the old roof insulation with newspaper and sawdust is lying freely against the beam, causing flies to pour in... How do I seal this up? There is about a 7 cm (and 2 m long) large gap. Spray foam? Or is there a better solution?

 

[cpalm]

Insect net? Available in narrow rolls for eaves.

 

[sizz]

Insect net? Available in narrow rolls for eaves.[/QUOTEj
Do I staple it to make it really tight?

Insect net? Available in narrow rolls for eaves.

Thanks, will it be tight enough if I staple it?